2023
Barrick J E; Blount Z D; Lake D M; Dwenger J H; Chavarria-Palma J E; Izutsu M; Wiser M J
Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli Journal Article
Journal of Visualized Experiments, 198 , pp. e65342, 2023, ISSN: 1940-087X.
Abstract | Links | BibTeX | Altmetric | Tags: Fitness Trajectories, Methods and Miscellaneous
@article{Barrick2023,
title = {Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli},
author = {Jeffrey E. Barrick and Zachary D. Blount and Devin M. Lake and Jack H. Dwenger and Jesus E. Chavarria-Palma and Minako Izutsu and Michael J. Wiser},
doi = {10.3791/65342},
issn = {1940-087X},
year = {2023},
date = {2023-08-18},
urldate = {2023-08-18},
journal = {Journal of Visualized Experiments},
volume = {198},
pages = {e65342},
abstract = {The Long-Term Evolution Experiment (LTEE) has followed twelve populations of \textit{Escherichia coli} as they have adapted to a simple laboratory environment for more than 35 years and 77,000 bacterial generations. The setup and procedures used in the LTEE epitomize reliable and reproducible methods for studying microbial evolution. In this protocol, we first describe how the LTEE populations are transferred to fresh medium and cultured each day. Then, we describe how the LTEE populations are regularly checked for possible signs of contamination and archived to provide a permanent frozen "fossil record" for later study. Multiple safeguards included in these procedures are designed to prevent contamination, detect various problems when they occur, and recover from disruptions without appreciably setting back the progress of the experiment. One way that the overall tempo and character of evolutionary changes are monitored in the LTEE is by measuring the competitive fitness of populations and strains from the experiment. We describe how co-culture competition assays are conducted and provide both a spreadsheet and an R package (fitnessR) for calculating relative fitness from the results. Over the course of the LTEE, the behaviors of some populations have changed in interesting ways, and new technologies like whole-genome sequencing have provided additional avenues for investigating how the populations have evolved. We end by discussing how the original LTEE procedures have been updated to accommodate or take advantage of these changes. This protocol will be useful for researchers who use the LTEE as a model system for studying connections between evolution and genetics, molecular biology, systems biology, and ecology. More broadly, the LTEE provides a tried-and-true template for those who are beginning their own evolution experiments with new microbes, environments, and questions. },
keywords = {Fitness Trajectories, Methods and Miscellaneous},
pubstate = {published},
tppubtype = {article}
}
The Long-Term Evolution Experiment (LTEE) has followed twelve populations of Escherichia coli as they have adapted to a simple laboratory environment for more than 35 years and 77,000 bacterial generations. The setup and procedures used in the LTEE epitomize reliable and reproducible methods for studying microbial evolution. In this protocol, we first describe how the LTEE populations are transferred to fresh medium and cultured each day. Then, we describe how the LTEE populations are regularly checked for possible signs of contamination and archived to provide a permanent frozen "fossil record" for later study. Multiple safeguards included in these procedures are designed to prevent contamination, detect various problems when they occur, and recover from disruptions without appreciably setting back the progress of the experiment. One way that the overall tempo and character of evolutionary changes are monitored in the LTEE is by measuring the competitive fitness of populations and strains from the experiment. We describe how co-culture competition assays are conducted and provide both a spreadsheet and an R package (fitnessR) for calculating relative fitness from the results. Over the course of the LTEE, the behaviors of some populations have changed in interesting ways, and new technologies like whole-genome sequencing have provided additional avenues for investigating how the populations have evolved. We end by discussing how the original LTEE procedures have been updated to accommodate or take advantage of these changes. This protocol will be useful for researchers who use the LTEE as a model system for studying connections between evolution and genetics, molecular biology, systems biology, and ecology. More broadly, the LTEE provides a tried-and-true template for those who are beginning their own evolution experiments with new microbes, environments, and questions.
Turner C B; Blount Z D; Mitchell D H; Lenski R E
Evolution of a cross-feeding interaction following a key innovation in a long-term evolution experiment with Escherichia coli Journal Article
Microbiology (Reading), 169 (8), 2023.
Abstract | Links | BibTeX | Altmetric | Tags: Citrate Evolution, Demography and Ecology, Historical Contingency
@article{Turner2023,
title = { Evolution of a cross-feeding interaction following a key innovation in a long-term evolution experiment with \textit{Escherichia coli} },
author = {Caroline B. Turner and Zachary D. Blount and Daniel H. Mitchell and Richard E. Lenski},
doi = {10.1099/mic.0.001390},
year = {2023},
date = {2023-08-01},
urldate = {2023-08-01},
journal = { Microbiology (Reading)},
volume = {169},
number = {8},
abstract = {The evolution of a novel trait can profoundly change an organism's effects on its environment, which can in turn affect the further evolution of that organism and any coexisting organisms. We examine these effects and feedbacks following the evolution of a novel function in the Long-Term Evolution Experiment (LTEE) with \textit{Escherichia coli}. A characteristic feature of \textit{E. coli} is its inability to grow aerobically on citrate (Cit^{−}). Nonetheless, a Cit^{+} variant with this capacity evolved in one LTEE population after 31 000 generations. The Cit^{+} clade then coexisted stably with another clade that retained the ancestral Cit^{−} phenotype. This coexistence was shaped by the evolution of a cross-feeding relationship based on C4-dicarboxylic acids, particularly succinate, fumarate, and malate, that the Cit^{+} variants release into the medium. Both the Cit^{−} and Cit^{+} cells evolved to grow on these excreted resources. The evolution of aerobic growth on citrate thus led to a transition from an ecosystem based on a single limiting resource, glucose, to one with at least five resources that were either shared or partitioned between the two coexisting clades. Our findings show that evolutionary novelties can change environmental conditions in ways that facilitate diversity by altering ecosystem structure and the evolutionary trajectories of coexisting lineages. },
keywords = {Citrate Evolution, Demography and Ecology, Historical Contingency},
pubstate = {published},
tppubtype = {article}
}
The evolution of a novel trait can profoundly change an organism's effects on its environment, which can in turn affect the further evolution of that organism and any coexisting organisms. We examine these effects and feedbacks following the evolution of a novel function in the Long-Term Evolution Experiment (LTEE) with Escherichia coli. A characteristic feature of E. coli is its inability to grow aerobically on citrate (Cit−). Nonetheless, a Cit+ variant with this capacity evolved in one LTEE population after 31 000 generations. The Cit+ clade then coexisted stably with another clade that retained the ancestral Cit− phenotype. This coexistence was shaped by the evolution of a cross-feeding relationship based on C4-dicarboxylic acids, particularly succinate, fumarate, and malate, that the Cit+ variants release into the medium. Both the Cit− and Cit+ cells evolved to grow on these excreted resources. The evolution of aerobic growth on citrate thus led to a transition from an ecosystem based on a single limiting resource, glucose, to one with at least five resources that were either shared or partitioned between the two coexisting clades. Our findings show that evolutionary novelties can change environmental conditions in ways that facilitate diversity by altering ecosystem structure and the evolutionary trajectories of coexisting lineages.
Mukherjee A; Ealy J; Huang Y; Benites N C; Polk M; Basan M
Coexisting ecotypes in long-term evolution emerged from interacting trade-offs Journal Article
Nature Communications, 14 (1), pp. 3805, 2023, ISSN: 2041-1723.
Abstract | Links | BibTeX | Altmetric | Tags: Demography and Ecology, Theory and Simulations
@article{Mukherjee2023,
title = {Coexisting ecotypes in long-term evolution emerged from interacting trade-offs},
author = {Avik Mukherjee and Jade Ealy and Yanqing Huang and Nina Catherine Benites and Mark Polk and Markus Basan},
url = {https://www.nature.com/articles/s41467-023-39471-9},
doi = {10.1038/s41467-023-39471-9},
issn = {2041-1723},
year = {2023},
date = {2023-06-26},
journal = {Nature Communications},
volume = {14},
number = {1},
pages = {3805},
abstract = {Evolution of complex communities of coexisting microbes remains poorly understood. The long-term evolution experiment on \textit{Escherichia coli} (LTEE) revealed the spontaneous emergence of stable coexistence of multiple ecotypes, which persisted for more than 14,000 generations of continuous evolution. Here, using a combination of experiments and computer simulations, we show that the emergence and persistence of this phenomenon can be explained by the combination of two interacting trade-offs, rooted in biochemical constraints: First, faster growth is enabled by higher fermentation and obligate acetate excretion. Second, faster growth results in longer lag times when utilizing acetate after glucose is depleted. This combination creates an ecological niche for a slower-growing ecotype, specialized in switching to acetate. These findings demonstrate that trade-offs can give rise to surprisingly complex communities with evolutionarily stable coexistence of multiple variants in even the simplest environments.},
keywords = {Demography and Ecology, Theory and Simulations},
pubstate = {published},
tppubtype = {article}
}
Evolution of complex communities of coexisting microbes remains poorly understood. The long-term evolution experiment on Escherichia coli (LTEE) revealed the spontaneous emergence of stable coexistence of multiple ecotypes, which persisted for more than 14,000 generations of continuous evolution. Here, using a combination of experiments and computer simulations, we show that the emergence and persistence of this phenomenon can be explained by the combination of two interacting trade-offs, rooted in biochemical constraints: First, faster growth is enabled by higher fermentation and obligate acetate excretion. Second, faster growth results in longer lag times when utilizing acetate after glucose is depleted. This combination creates an ecological niche for a slower-growing ecotype, specialized in switching to acetate. These findings demonstrate that trade-offs can give rise to surprisingly complex communities with evolutionarily stable coexistence of multiple variants in even the simplest environments.
Lenski R E
Revisiting the design of the long-term evolution experiment with Escherichia coli Journal Article
Journal of Molecular Evolution, 91 (3), pp. 241-253, 2023.
Abstract | Links | BibTeX | Altmetric | Tags: Citrate Evolution, Descendant Experiments, Fitness Trajectories, Genome Evolution, Methods and Miscellaneous, Review Articles
@article{lenski2023,
title = {Revisiting the design of the long-term evolution experiment with \textit{Escherichia coli}},
author = {Richard E. Lenski},
url = {https://link.springer.com/epdf/10.1007/s00239-023-10095-3?sharing_token=zmDHuK0kbvnJBQq1k96fe_e4RwlQNchNByi7wbcMAY53KNkhv6F2YgRIeC8sZGNejxJrvlAGZWInruED5Dqdai5WeU2RAWL2PJNp0pL9QJO39B_ijCtRZcaW8jqM7PclDJfFwL_78U5zNlQYyCOsQwa1Yxha61uXUWhW-Buiq7o=},
doi = {10.1007/s00239-023-10095-3},
year = {2023},
date = {2023-06-01},
urldate = {2023-02-15},
journal = {Journal of Molecular Evolution},
volume = {91},
number = {3},
pages = {241-253},
abstract = {The long-term evolution experiment (LTEE) with \textit{Escherichia coli} began in 1988 and it continues to this day, with its 12 populations having recently reached 75,000 generations of evolution in a simple, well-controlled environment. The LTEE was designed to explore open-ended questions about the dynamics and repeatability of phenotypic and genetic evolution. Here I discuss various aspects of the LTEE’s experimental design that have enabled its stability and success, including the choices of the culture regime, growth medium, ancestral strain, and statistical replication. I also discuss some of the challenges associated with a long-running project, such as handling procedural errors (e.g., cross-contamination) and managing the expanding collection of frozen samples. The simplicity of the experimental design and procedures have supported the long-term stability of the LTEE. That stability—along with the inherent creativity of the evolutionary process and the emergence of new genomic technologies—provides a platform that has allowed talented students and collaborators to pose questions, collect data, and make discoveries that go far beyond anything I could have imagined at the start of the LTEE.},
keywords = {Citrate Evolution, Descendant Experiments, Fitness Trajectories, Genome Evolution, Methods and Miscellaneous, Review Articles},
pubstate = {published},
tppubtype = {article}
}
The long-term evolution experiment (LTEE) with Escherichia coli began in 1988 and it continues to this day, with its 12 populations having recently reached 75,000 generations of evolution in a simple, well-controlled environment. The LTEE was designed to explore open-ended questions about the dynamics and repeatability of phenotypic and genetic evolution. Here I discuss various aspects of the LTEE’s experimental design that have enabled its stability and success, including the choices of the culture regime, growth medium, ancestral strain, and statistical replication. I also discuss some of the challenges associated with a long-running project, such as handling procedural errors (e.g., cross-contamination) and managing the expanding collection of frozen samples. The simplicity of the experimental design and procedures have supported the long-term stability of the LTEE. That stability—along with the inherent creativity of the evolutionary process and the emergence of new genomic technologies—provides a platform that has allowed talented students and collaborators to pose questions, collect data, and make discoveries that go far beyond anything I could have imagined at the start of the LTEE.
Jagdish T
The dynamics of fitness and pleiotropy in a long-term evolution experiment with Escherichia coli PhD Thesis
2023.
Abstract | Links | BibTeX | Tags: Correlated Responses, Demography and Ecology, Fitness Trajectories, Methods and Miscellaneous
@phdthesis{nokey,
title = {The dynamics of fitness and pleiotropy in a long-term evolution experiment with \textit{Escherichia coli}},
author = {Tanush Jagdish},
url = {https://dash.harvard.edu/handle/1/37375541},
year = {2023},
date = {2023-05-08},
urldate = {2023-05-08},
abstract = {Life on earth is shaped by a delicate balance between chance and necessity. A combination of natural selection and genetic drift has moulded random genetic variations over the course of billions of years to generate the complex and interconnected biosphere we see today. These evolutionary dynamics are ultimately the product of numerous genetic mechanisms operating in genomes with highly complex architectures. Unravelling the rules of genetic mechanisms responsible for evolutionary innovation is critical to developing a comprehensive and predictive evolutionary theory, but has evaded direct experimentation since the scale of resources and technology needed to study the patterns of genetic evolution has only recently become achievable. In this dissertation, I explore the use of microbial experimental evolution as a powerful tool for probing evolutionary questions, particularly by leveraging DNA-barcoding and high-throughput DNA sequencing. In chapter 1, I provide an overview of the field of microbial experimental evolution, dividing its history into two eras marked by qualitatively different methodological advancements. I make the case that we now stand at the dawn of a third era, where advances in genome-engineering coupled with low-cost, high-throughput DNA sequencing will allow experiments to finally probe evolution on a statistical scale. I then present two research studies that take advantage of microbial experimental evolution to investigate distinct genetic mechanisms key to the evolutionary process. In Chapter 2, I explore whether fitness can continue increasing in a population that has already adapted to its environment for over 30,000 generations, and whether fixations of beneficial mutations from population-wide DNA sequencing can predict jumps in fitness. My findings reveal that fitness continues to monotonically increase in step with the fixation of beneficial mutations, even though the rate of fixation has dramatically slowed down, highlighting the potential for ongoing adaptation even under constant environmental conditions. In Chapter 3, I develop a novel conjugation-based DNA-barcoding method for the Long-Term Evolution Experiment (LTEE) with \textit{Escherichia coli}, allowing me to examine the pleiotropic consequences of adaptation to glucose over 50,000 generations in 15 novel resource environments. My observations reveal broad patterns of both convergent and divergent evolution that correspond with mutations in key metabolic genes in clonal sequencing datasets, shedding light on the nature of pleiotropy and its evolution over extended timescales. Using microbial model systems in an evolutionary context has the unique advantage of being relevant both to fundamental evolutionary biology and human health. Since genetic drift and rare mutational events both play an outsized role in determining the evolutionary trajectories of populations, evolutionary questions in the modern age will increasingly be faced with issues of scale. Microbial experimental evolution offers both scale and tractability to solve this problem. Uniquely, this does not sacrifice on human relevance. Building a coarse-grained and comprehensive evolutionary theory is more significant to society today than ever before as the importance of clonal evolution in cancer, gut microbiomes and even pandemics becomes more clearly understood.},
keywords = {Correlated Responses, Demography and Ecology, Fitness Trajectories, Methods and Miscellaneous},
pubstate = {published},
tppubtype = {phdthesis}
}
Life on earth is shaped by a delicate balance between chance and necessity. A combination of natural selection and genetic drift has moulded random genetic variations over the course of billions of years to generate the complex and interconnected biosphere we see today. These evolutionary dynamics are ultimately the product of numerous genetic mechanisms operating in genomes with highly complex architectures. Unravelling the rules of genetic mechanisms responsible for evolutionary innovation is critical to developing a comprehensive and predictive evolutionary theory, but has evaded direct experimentation since the scale of resources and technology needed to study the patterns of genetic evolution has only recently become achievable. In this dissertation, I explore the use of microbial experimental evolution as a powerful tool for probing evolutionary questions, particularly by leveraging DNA-barcoding and high-throughput DNA sequencing. In chapter 1, I provide an overview of the field of microbial experimental evolution, dividing its history into two eras marked by qualitatively different methodological advancements. I make the case that we now stand at the dawn of a third era, where advances in genome-engineering coupled with low-cost, high-throughput DNA sequencing will allow experiments to finally probe evolution on a statistical scale. I then present two research studies that take advantage of microbial experimental evolution to investigate distinct genetic mechanisms key to the evolutionary process. In Chapter 2, I explore whether fitness can continue increasing in a population that has already adapted to its environment for over 30,000 generations, and whether fixations of beneficial mutations from population-wide DNA sequencing can predict jumps in fitness. My findings reveal that fitness continues to monotonically increase in step with the fixation of beneficial mutations, even though the rate of fixation has dramatically slowed down, highlighting the potential for ongoing adaptation even under constant environmental conditions. In Chapter 3, I develop a novel conjugation-based DNA-barcoding method for the Long-Term Evolution Experiment (LTEE) with Escherichia coli, allowing me to examine the pleiotropic consequences of adaptation to glucose over 50,000 generations in 15 novel resource environments. My observations reveal broad patterns of both convergent and divergent evolution that correspond with mutations in key metabolic genes in clonal sequencing datasets, shedding light on the nature of pleiotropy and its evolution over extended timescales. Using microbial model systems in an evolutionary context has the unique advantage of being relevant both to fundamental evolutionary biology and human health. Since genetic drift and rare mutational events both play an outsized role in determining the evolutionary trajectories of populations, evolutionary questions in the modern age will increasingly be faced with issues of scale. Microbial experimental evolution offers both scale and tractability to solve this problem. Uniquely, this does not sacrifice on human relevance. Building a coarse-grained and comprehensive evolutionary theory is more significant to society today than ever before as the importance of clonal evolution in cancer, gut microbiomes and even pandemics becomes more clearly understood.
Limdi A; Owen S V; Herren C; Lenski R E; Baym M
Parallel changes in gene essentiality over 50,000 generations of evolution Unpublished
2023.
Abstract | Links | BibTeX | Altmetric | Tags: Fitness Trajectories, Genome Evolution, Parallelism and Divergence
@unpublished{Limdi2023,
title = {Parallel changes in gene essentiality over 50,000 generations of evolution},
author = {Anurag Limdi and Siân V. Owen and Cristina Herren and Richard E. Lenski and Michael Baym},
url = {https://www.biorxiv.org/content/10.1101/2022.05.17.492023v2},
doi = {10.1101/2022.05.17.492023},
year = {2023},
date = {2023-03-07},
urldate = {2023-03-07},
journal = {bioRxiv},
publisher = {Cold Spring Harbor Laboratory},
abstract = {Over evolutionary time, bacteria face changing environments, which may require different sets of genes for survival. As they adapt to a specific constant environment, some genes are modified and lost, which can increase fitness while also modulating the effects of further gene losses. However, whether evolutionary specialization leads to systematic changes in robustness to gene loss is largely unexplored. Here, we compare the effects of insertion mutations in \textit{Escherichia coli} between ancestral and 12 independently derived strains after 50,000 generations of growth in a simple, uniform environment. We find that epistasis between insertion mutations and genetic background is common, but the overall distribution of fitness effects is largely unchanged. In particular, we see systematic changes in gene essentiality, with more genes becoming essential over evolution than vice versa. The resulting changes often occurred in parallel across the independently evolving populations. A few of the changes in gene essentiality are associated with large structural variations, but most are not. Taken together, our results demonstrate that gene essentiality is a dynamic, evolvable property, and they suggest that changes in gene essentiality are a result of natural selection in this long-term evolution experiment, rather than a mere byproduct of structural changes.},
keywords = {Fitness Trajectories, Genome Evolution, Parallelism and Divergence},
pubstate = {published},
tppubtype = {unpublished}
}
Over evolutionary time, bacteria face changing environments, which may require different sets of genes for survival. As they adapt to a specific constant environment, some genes are modified and lost, which can increase fitness while also modulating the effects of further gene losses. However, whether evolutionary specialization leads to systematic changes in robustness to gene loss is largely unexplored. Here, we compare the effects of insertion mutations in Escherichia coli between ancestral and 12 independently derived strains after 50,000 generations of growth in a simple, uniform environment. We find that epistasis between insertion mutations and genetic background is common, but the overall distribution of fitness effects is largely unchanged. In particular, we see systematic changes in gene essentiality, with more genes becoming essential over evolution than vice versa. The resulting changes often occurred in parallel across the independently evolving populations. A few of the changes in gene essentiality are associated with large structural variations, but most are not. Taken together, our results demonstrate that gene essentiality is a dynamic, evolvable property, and they suggest that changes in gene essentiality are a result of natural selection in this long-term evolution experiment, rather than a mere byproduct of structural changes.
Couce A; Magnan M; Lenski R E; Tenaillon O
Predictability shifts from local to global rules during bacterial adaptation Unpublished
2023.
Abstract | Links | BibTeX | Altmetric | Tags: Fitness Trajectories, Genome Evolution, Historical Contingency
@unpublished{Couce2023,
title = {Predictability shifts from local to global rules during bacterial adaptation},
author = {Alejandro Couce and Melanie Magnan and Richard E. Lenski and Olivier Tenaillon},
url = {https://www.biorxiv.org/content/early/2022/05/17/2022.05.17.492360},
doi = {10.1101/2022.05.17.492360},
year = {2023},
date = {2023-01-30},
urldate = {2022-01-01},
journal = {bioRxiv},
publisher = {Cold Spring Harbor Laboratory},
abstract = {Understanding the distribution of fitness effects of new mutations is central to predicting adaptive evolution. Short-term experiments provide a snapshot of this distribution, but observing how it changes as organisms adapt is challenging. Here we use saturated, genome-wide insertion libraries to quantify how the fitness effects of new mutations changed in two \textit{E. coli} populations that adapted to a constant environment for 15,000 generations. The proportions of neutral and deleterious mutations remained constant, despite fitness gains of ∼50%. In contrast, the beneficial fraction declined rapidly and became exponentially distributed, with genetic interactions profoundly reshuffling the loci subject to beneficial mutations. Despite this volatility, the ancestral distribution predicts many of the alleles that become dominant in the long-term experiment, even after the initial period of rapid adaptation. Overall, our results suggest that short-term adaptation can be idiosyncratic but empirically reproducible, and that long-term dynamics can be described by simple statistical principles.},
keywords = {Fitness Trajectories, Genome Evolution, Historical Contingency},
pubstate = {published},
tppubtype = {unpublished}
}
Understanding the distribution of fitness effects of new mutations is central to predicting adaptive evolution. Short-term experiments provide a snapshot of this distribution, but observing how it changes as organisms adapt is challenging. Here we use saturated, genome-wide insertion libraries to quantify how the fitness effects of new mutations changed in two E. coli populations that adapted to a constant environment for 15,000 generations. The proportions of neutral and deleterious mutations remained constant, despite fitness gains of ∼50%. In contrast, the beneficial fraction declined rapidly and became exponentially distributed, with genetic interactions profoundly reshuffling the loci subject to beneficial mutations. Despite this volatility, the ancestral distribution predicts many of the alleles that become dominant in the long-term experiment, even after the initial period of rapid adaptation. Overall, our results suggest that short-term adaptation can be idiosyncratic but empirically reproducible, and that long-term dynamics can be described by simple statistical principles.
Ascensao J A; Wetmore K M; Good B H; Arkin A P; Hallatschek O
Quantifying the adaptive potential of a nascent bacterial community Journal Article
Nature Communications, 14 (1), pp. 248, 2023.
Abstract | Links | BibTeX | Altmetric | Tags: Demography and Ecology, Descendant Experiments, Genome Evolution, Genotypes and Phenotypes
@article{ascensao2023,
title = {Quantifying the adaptive potential of a nascent bacterial community},
author = {Joao A. Ascensao and Kelly M. Wetmore and Benjamin H. Good and Adam P. Arkin and Oskar Hallatschek},
url = {https://www.nature.com/articles/s41467-022-35677-5},
doi = {10.1038/s41467-022-35677-5},
year = {2023},
date = {2023-01-16},
urldate = {2022-01-01},
journal = {Nature Communications},
volume = {14},
number = {1},
pages = {248},
publisher = {Cold Spring Harbor Laboratory},
abstract = {The fitness effects of all possible mutations available to an organism largely shape the dynamics of evolutionary adaptation. Yet, whether and how this adaptive landscape changes over evolutionary times, especially upon ecological diversification and changes in community composition, remains poorly understood. We sought to fill this gap by analyzing a stable community of two closely related ecotypes (“L” and “S”) shortly after they emerged within the \textit{E. coli} Long-Term Evolution Experiment (LTEE). We engineered genome-wide barcoded transposon libraries to measure the invasion fitness effects of all possible gene knockouts in the coexisting strains as well as their ancestor, for many different, ecologically relevant conditions. We find consistent statistical patterns of fitness effect variation across both genetic background and community composition, despite the idiosyncratic behavior of individual knockouts. Additionally, fitness effects are correlated with evolutionary outcomes for a number of conditions, possibly revealing shifting patterns of adaptation. Together, our results reveal how ecological and epistatic effects combine to shape the adaptive landscape in a nascent ecological community.},
keywords = {Demography and Ecology, Descendant Experiments, Genome Evolution, Genotypes and Phenotypes},
pubstate = {published},
tppubtype = {article}
}
The fitness effects of all possible mutations available to an organism largely shape the dynamics of evolutionary adaptation. Yet, whether and how this adaptive landscape changes over evolutionary times, especially upon ecological diversification and changes in community composition, remains poorly understood. We sought to fill this gap by analyzing a stable community of two closely related ecotypes (“L” and “S”) shortly after they emerged within the E. coli Long-Term Evolution Experiment (LTEE). We engineered genome-wide barcoded transposon libraries to measure the invasion fitness effects of all possible gene knockouts in the coexisting strains as well as their ancestor, for many different, ecologically relevant conditions. We find consistent statistical patterns of fitness effect variation across both genetic background and community composition, despite the idiosyncratic behavior of individual knockouts. Additionally, fitness effects are correlated with evolutionary outcomes for a number of conditions, possibly revealing shifting patterns of adaptation. Together, our results reveal how ecological and epistatic effects combine to shape the adaptive landscape in a nascent ecological community.
2022
Laurin D; Mercier C; Quansah N; Robert J S; Usson Y; Schneider D; Hindré T; Schaack B
Extracellular vesicles from 50,000 generation clones of the Escherichia coli long-term evolution experiment Journal Article
International Journal of Molecular Sciences, 23 , pp. 14580, 2022, ISSN: 1422-0067.
Abstract | Links | BibTeX | Altmetric | Tags: Cell Morphology, Genotypes and Phenotypes
@article{Laurin2022,
title = {Extracellular vesicles from 50,000 generation clones of the \textit{Escherichia coli} long-term evolution experiment},
author = {David Laurin and Corinne Mercier and Nyamekye Quansah and Julie Suzanne Robert and Yves Usson and Dominique Schneider and Thomas Hindré and Béatrice Schaack },
url = {https://www.mdpi.com/1422-0067/23/23/14580},
doi = {10.3390/ijms232314580},
issn = {1422-0067},
year = {2022},
date = {2022-11-01},
urldate = {2022-11-01},
journal = {International Journal of Molecular Sciences},
volume = {23},
pages = {14580},
abstract = {Extracellular vesicles (EVs) are critical elements of cell–cell communication. Here, we characterized the outer membrane vesicles (OMVs) released by specific clones of Escherichia coli isolated from the Long-Term Evolution Experiment after 50,000 generations (50K) of adaptation to glucose minimal medium. Compared with their ancestor, the evolved clones produce small OMVs but also larger ones which display variable amounts of both OmpA and LPS. Tracking ancestral, fluorescently labelled OMVs revealed that they fuse with both ancestral- and 50K-evolved cells, albeit in different proportions. We quantified that less than 2% of the cells from one 50K-evolved clone acquired the fluorescence delivered by OMVs from the ancestral strain but that one cell concomitantly fuses with several OMVs. Globally, our results showed that OMV production in E. coli is a phenotype that varies along bacterial evolution and question the contribution of OMVs-mediated interactions in bacterial adaptation.},
keywords = {Cell Morphology, Genotypes and Phenotypes},
pubstate = {published},
tppubtype = {article}
}
Extracellular vesicles (EVs) are critical elements of cell–cell communication. Here, we characterized the outer membrane vesicles (OMVs) released by specific clones of Escherichia coli isolated from the Long-Term Evolution Experiment after 50,000 generations (50K) of adaptation to glucose minimal medium. Compared with their ancestor, the evolved clones produce small OMVs but also larger ones which display variable amounts of both OmpA and LPS. Tracking ancestral, fluorescently labelled OMVs revealed that they fuse with both ancestral- and 50K-evolved cells, albeit in different proportions. We quantified that less than 2% of the cells from one 50K-evolved clone acquired the fluorescence delivered by OMVs from the ancestral strain but that one cell concomitantly fuses with several OMVs. Globally, our results showed that OMV production in E. coli is a phenotype that varies along bacterial evolution and question the contribution of OMVs-mediated interactions in bacterial adaptation.
Favate J S; Liang S; Cope A L; Yadavilli S S; Shah P
The landscape of transcriptional and translational changes over 22 years of bacterial adaptation Journal Article
eLife, 11 , pp. e81979, 2022.
Abstract | Links | BibTeX | Altmetric | Tags: Genotypes and Phenotypes, Parallelism and Divergence
@article{favate2022,
title = {The landscape of transcriptional and translational changes over 22 years of bacterial adaptation},
author = {John S. Favate AND Shun Liang AND Alexander L. Cope AND Srujana S. Yadavilli AND Premal Shah},
editor = {Detlef Weigel},
url = {https://elifesciences.org/articles/81979},
doi = {10.7554/eLife.81979},
year = {2022},
date = {2022-10-10},
urldate = {2022-10-10},
journal = {eLife},
volume = {11},
pages = {e81979},
abstract = {Organisms can adapt to an environment by taking multiple mutational paths. This redundancy at the genetic level, where many mutations have similar phenotypic and fitness effects, can make untangling the molecular mechanisms of complex adaptations difficult. Here, we use the \textit{Escherichia coli} long-term evolution experiment (LTEE) as a model to address this challenge. To understand how different genomic changes could lead to parallel fitness gains, we characterize the landscape of transcriptional and translational changes across 12 replicate populations evolving in parallel for 50,000 generations. By quantifying absolute changes in mRNA abundances, we show that not only do all evolved lines have more mRNAs but that this increase in mRNA abundance scales with cell size. We also find that despite few shared mutations at the genetic level, clones from replicate populations in the LTEE are remarkably similar in their gene expression patterns at both the transcriptional and translational levels. Furthermore, we show that the majority of the expression changes are due to changes at the transcriptional level with very few translational changes. Finally, we show how mutations in transcriptional regulators lead to consistent and parallel changes in the expression levels of downstream genes. These results deepen our understanding of the molecular mechanisms underlying complex adaptations and provide insights into the repeatability of evolution.},
howpublished = {eLife},
keywords = {Genotypes and Phenotypes, Parallelism and Divergence},
pubstate = {published},
tppubtype = {article}
}
Organisms can adapt to an environment by taking multiple mutational paths. This redundancy at the genetic level, where many mutations have similar phenotypic and fitness effects, can make untangling the molecular mechanisms of complex adaptations difficult. Here, we use the Escherichia coli long-term evolution experiment (LTEE) as a model to address this challenge. To understand how different genomic changes could lead to parallel fitness gains, we characterize the landscape of transcriptional and translational changes across 12 replicate populations evolving in parallel for 50,000 generations. By quantifying absolute changes in mRNA abundances, we show that not only do all evolved lines have more mRNAs but that this increase in mRNA abundance scales with cell size. We also find that despite few shared mutations at the genetic level, clones from replicate populations in the LTEE are remarkably similar in their gene expression patterns at both the transcriptional and translational levels. Furthermore, we show that the majority of the expression changes are due to changes at the transcriptional level with very few translational changes. Finally, we show how mutations in transcriptional regulators lead to consistent and parallel changes in the expression levels of downstream genes. These results deepen our understanding of the molecular mechanisms underlying complex adaptations and provide insights into the repeatability of evolution.
Izutsu M; Lenski R E
Experimental test of the contributions of initial variation and new mutations to adaptive evolution in a novel environment Journal Article
Frontiers in Ecology and Evolution, 10 , pp. 958406, 2022, ISSN: 2296-701X.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments, Historical Contingency, Parallelism and Divergence
@article{izutsu2022,
title = {Experimental test of the contributions of initial variation and new mutations to adaptive evolution in a novel environment},
author = {Minako Izutsu and Richard E. Lenski},
url = {https://www.frontiersin.org/articles/10.3389/fevo.2022.958406/full},
doi = {10.3389/fevo.2022.958406},
issn = {2296-701X},
year = {2022},
date = {2022-10-06},
urldate = {2022-10-01},
journal = {Frontiers in Ecology and Evolution},
volume = {10},
pages = {958406},
abstract = {Experimental evolution is an approach that allows researchers to study organisms as they evolve in controlled environments. Despite the growing popularity of this approach, there are conceptual gaps among projects that use different experimental designs. One such gap concerns the contributions to adaptation of genetic variation present at the start of an experiment and that of new mutations that arise during an experiment. The primary source of genetic variation has historically depended largely on the study organisms. In the long-term evolution experiment (LTEE) using \textit{Escherichia coli}, for example, each population started from a single haploid cell, and therefore, adaptation depended entirely on new mutations. Most other microbial evolution experiments have followed the same strategy. By contrast, evolution experiments using multicellular, sexually reproducing organisms typically start with preexisting variation that fuels the response to selection. New mutations may also come into play in later generations of these experiments, but it is generally difficult to quantify their contribution in these studies. Here, we performed an experiment using \textit{E. coli} to compare the contributions of initial genetic variation and new mutations to adaptation in a new environment. Our experiment had four treatments that varied in their starting diversity, with 18 populations in each treatment. One treatment depended entirely on new mutations, while the other three began with mixtures of clones, whole-population samples, or mixtures of whole-population samples from the LTEE. We tracked a genetic marker associated with different founders in two treatments. These data revealed significant variation in fitness among the founders, and that variation impacted evolution in the early generations of our experiment. However, there were no differences in fitness among the treatments after 500 or 2,000 generations in the new environment, despite the variation in fitness among the founders. These results indicate that new mutations quickly dominated, and eventually they contributed more to adaptation than did the initial variation. Our study thus shows that preexisting genetic variation can have a strong impact on early evolution in a new environment, but new beneficial mutations may contribute more to later evolution and can even drive some initially beneficial variants to extinction.},
keywords = {Descendant Experiments, Historical Contingency, Parallelism and Divergence},
pubstate = {published},
tppubtype = {article}
}
Experimental evolution is an approach that allows researchers to study organisms as they evolve in controlled environments. Despite the growing popularity of this approach, there are conceptual gaps among projects that use different experimental designs. One such gap concerns the contributions to adaptation of genetic variation present at the start of an experiment and that of new mutations that arise during an experiment. The primary source of genetic variation has historically depended largely on the study organisms. In the long-term evolution experiment (LTEE) using Escherichia coli, for example, each population started from a single haploid cell, and therefore, adaptation depended entirely on new mutations. Most other microbial evolution experiments have followed the same strategy. By contrast, evolution experiments using multicellular, sexually reproducing organisms typically start with preexisting variation that fuels the response to selection. New mutations may also come into play in later generations of these experiments, but it is generally difficult to quantify their contribution in these studies. Here, we performed an experiment using E. coli to compare the contributions of initial genetic variation and new mutations to adaptation in a new environment. Our experiment had four treatments that varied in their starting diversity, with 18 populations in each treatment. One treatment depended entirely on new mutations, while the other three began with mixtures of clones, whole-population samples, or mixtures of whole-population samples from the LTEE. We tracked a genetic marker associated with different founders in two treatments. These data revealed significant variation in fitness among the founders, and that variation impacted evolution in the early generations of our experiment. However, there were no differences in fitness among the treatments after 500 or 2,000 generations in the new environment, despite the variation in fitness among the founders. These results indicate that new mutations quickly dominated, and eventually they contributed more to adaptation than did the initial variation. Our study thus shows that preexisting genetic variation can have a strong impact on early evolution in a new environment, but new beneficial mutations may contribute more to later evolution and can even drive some initially beneficial variants to extinction.
Smith C E; Smith A N H; Cooper T F; Moore F B -G
Fitness of evolving bacterial populations is contingent on deep and shallow history but only shallow history creates predictable patterns Journal Article
Proceedings of the Royal Society B: Biological Sciences, 289 (1982), pp. 20221292, 2022.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments, Fitness Trajectories, Genotypes and Phenotypes, Historical Contingency
@article{smith2022,
title = {Fitness of evolving bacterial populations is contingent on deep and shallow history but only shallow history creates predictable patterns},
author = {Chelsea E. Smith AND Adam N. H. Smith AND Tim F. Cooper AND Francisco B.-G. Moore},
url = {https://royalsocietypublishing.org/doi/10.1098/rspb.2022.1292},
doi = {10.1098/rspb.2022.1292},
year = {2022},
date = {2022-09-14},
journal = {Proceedings of the Royal Society B: Biological Sciences},
volume = {289},
number = {1982},
pages = {20221292},
abstract = {Long-term evolution experiments have tested the importance of genetic and environmental factors in influencing evolutionary outcomes. Differences in phylogenetic history, recent adaptation to distinct environments and chance events, all influence the fitness of a population. However, the interplay of these factors on a population's evolutionary potential remains relatively unexplored. We tracked the outcome of 2000 generations of evolution of four natural isolates of \textit{Escherichia coli} bacteria that were engineered to also create differences in shallow history by adding previously identified mutations selected in a separate long-term experiment. Replicate populations started from each progenitor evolved in four environments. We found that deep and shallow phylogenetic histories both contributed significantly to differences in evolved fitness, though by different amounts in different selection environments. With one exception, chance effects were not significant. Whereas the effect of deep history did not follow any detectable pattern, effects of shallow history followed a pattern of diminishing returns whereby fitter ancestors had smaller fitness increases. These results are consistent with adaptive evolution being contingent on the interaction of several evolutionary forces but demonstrate that the nature of these interactions is not fixed and may not be predictable even when the role of chance is small.},
keywords = {Descendant Experiments, Fitness Trajectories, Genotypes and Phenotypes, Historical Contingency},
pubstate = {published},
tppubtype = {article}
}
Long-term evolution experiments have tested the importance of genetic and environmental factors in influencing evolutionary outcomes. Differences in phylogenetic history, recent adaptation to distinct environments and chance events, all influence the fitness of a population. However, the interplay of these factors on a population's evolutionary potential remains relatively unexplored. We tracked the outcome of 2000 generations of evolution of four natural isolates of Escherichia coli bacteria that were engineered to also create differences in shallow history by adding previously identified mutations selected in a separate long-term experiment. Replicate populations started from each progenitor evolved in four environments. We found that deep and shallow phylogenetic histories both contributed significantly to differences in evolved fitness, though by different amounts in different selection environments. With one exception, chance effects were not significant. Whereas the effect of deep history did not follow any detectable pattern, effects of shallow history followed a pattern of diminishing returns whereby fitter ancestors had smaller fitness increases. These results are consistent with adaptive evolution being contingent on the interaction of several evolutionary forces but demonstrate that the nature of these interactions is not fixed and may not be predictable even when the role of chance is small.
Maddamsetti R; Grant N A
Discovery of positive and purifying selection in metagenomic time series of hypermutator microbial populations Journal Article
PLOS Genetics, 18 (8), pp. e1010324, 2022, ISSN: 1553-7404.
Abstract | Links | BibTeX | Altmetric | Tags: Genome Evolution, Mutation Rates
@article{maddamsetti2022,
title = {Discovery of positive and purifying selection in metagenomic time series of hypermutator microbial populations},
author = { Rohan Maddamsetti and Nkrumah A. Grant},
editor = {Jianzhi Zhang},
url = {https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1010324},
doi = {10.1371/journal.pgen.1010324},
issn = {1553-7404},
year = {2022},
date = {2022-08-18},
urldate = {2022-08-18},
journal = {PLOS Genetics},
volume = {18},
number = {8},
pages = {e1010324},
abstract = {A general method to infer both positive and purifying selection during the real-time evolution of hypermutator pathogens would be broadly useful. To this end, we introduce a simple test to infer mode of selection (STIMS) from metagenomic time series of evolving microbial populations. We test STIMS on metagenomic data generated by simulations of bacterial evolution, and on metagenomic data spanning 62,750 generations of Lenski’s long-term evolution experiment with \textit{Escherichia coli} (LTEE). This benchmarking shows that STIMS detects positive selection in both nonmutator and hypermutator populations, and purifying selection in hypermutator populations. Using STIMS, we find strong evidence of ongoing positive selection on key regulators of the \textit{E. coli} gene regulatory network, even in some hypermutator populations. STIMS also detects positive selection on regulatory genes in hypermutator populations of \textit{Pseudomonas aeruginosa} that adapted to subinhibitory concentrations of colistin—an antibiotic of last resort—for just twenty-six days of laboratory evolution. Our results show that the fine-tuning of gene regulatory networks is a general mechanism for rapid and ongoing adaptation. The simplicity of STIMS, together with its intuitive visual interpretation, make it a useful test for positive and purifying selection in metagenomic data sets that track microbial evolution in real-time.},
key = {Maddamsetti2022},
keywords = {Genome Evolution, Mutation Rates},
pubstate = {published},
tppubtype = {article}
}
A general method to infer both positive and purifying selection during the real-time evolution of hypermutator pathogens would be broadly useful. To this end, we introduce a simple test to infer mode of selection (STIMS) from metagenomic time series of evolving microbial populations. We test STIMS on metagenomic data generated by simulations of bacterial evolution, and on metagenomic data spanning 62,750 generations of Lenski’s long-term evolution experiment with Escherichia coli (LTEE). This benchmarking shows that STIMS detects positive selection in both nonmutator and hypermutator populations, and purifying selection in hypermutator populations. Using STIMS, we find strong evidence of ongoing positive selection on key regulators of the E. coli gene regulatory network, even in some hypermutator populations. STIMS also detects positive selection on regulatory genes in hypermutator populations of Pseudomonas aeruginosa that adapted to subinhibitory concentrations of colistin—an antibiotic of last resort—for just twenty-six days of laboratory evolution. Our results show that the fine-tuning of gene regulatory networks is a general mechanism for rapid and ongoing adaptation. The simplicity of STIMS, together with its intuitive visual interpretation, make it a useful test for positive and purifying selection in metagenomic data sets that track microbial evolution in real-time.
Marshall D J; Malerba M; Lines T; Sezmis A L; Hasan C M; Lenski R E; McDonald M J
Long-term experimental evolution decouples size and production costs in Escherichia coli Journal Article
Proceedings of the National Academy of Sciences of the United States of America, 119 (21), pp. e2200713119, 2022.
Abstract | Links | BibTeX | Altmetric | Tags: Cell Morphology, Demography and Ecology
@article{marshall2021,
title = {Long-term experimental evolution decouples size and production costs in \emph{Escherichia coli}},
author = {Dustin J. Marshall and Martino Malerba and Thomas Lines and Aysha L. Sezmis and Chowdhury M. Hasan and Richard E. Lenski and Michael J. McDonald},
editor = {Ruth Shaw},
url = {https://pnas.org/doi/full/10.1073/pnas.2200713119},
doi = {10.1073/pnas.2200713119},
year = {2022},
date = {2022-05-20},
urldate = {2022-05-20},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
volume = {119},
number = {21},
pages = {e2200713119},
abstract = {Body size covaries with population dynamics across life’s domains. Metabolism may impose fundamental constraints on the coevolution of size and demography, but experimental tests of the causal links remain elusive. We leverage a 60,000-generation experiment in which \textit{Escherichia coli} populations evolved larger cells to examine intraspecific metabolic scaling and correlations with demographic parameters. Over the course of their evolution, the cells have roughly doubled in size relative to their ancestors. These larger cells have metabolic rates that are absolutely higher, but relative to their size, they are lower. Metabolic theory successfully predicted the relations between size, metabolism, and maximum population density, including support for Damuth’s law of energy equivalence, such that populations of larger cells achieved lower maximum densities but higher maximum biomasses than populations of smaller cells. The scaling of metabolism with cell size thus predicted the scaling of size with maximum population density. In stark contrast to standard theory, however, populations of larger cells grew faster than those of smaller cells, contradicting the fundamental and intuitive assumption that the costs of building new individuals should scale directly with their size. The finding that the costs of production can be decoupled from size necessitates a reevaluation of the evolutionary drivers and ecological consequences of biological size more generally.},
howpublished = {bioRxiv},
keywords = {Cell Morphology, Demography and Ecology},
pubstate = {published},
tppubtype = {article}
}
Body size covaries with population dynamics across life’s domains. Metabolism may impose fundamental constraints on the coevolution of size and demography, but experimental tests of the causal links remain elusive. We leverage a 60,000-generation experiment in which Escherichia coli populations evolved larger cells to examine intraspecific metabolic scaling and correlations with demographic parameters. Over the course of their evolution, the cells have roughly doubled in size relative to their ancestors. These larger cells have metabolic rates that are absolutely higher, but relative to their size, they are lower. Metabolic theory successfully predicted the relations between size, metabolism, and maximum population density, including support for Damuth’s law of energy equivalence, such that populations of larger cells achieved lower maximum densities but higher maximum biomasses than populations of smaller cells. The scaling of metabolism with cell size thus predicted the scaling of size with maximum population density. In stark contrast to standard theory, however, populations of larger cells grew faster than those of smaller cells, contradicting the fundamental and intuitive assumption that the costs of building new individuals should scale directly with their size. The finding that the costs of production can be decoupled from size necessitates a reevaluation of the evolutionary drivers and ecological consequences of biological size more generally.
Mathé-Hubert H; Amie R; Martin M; Gaffé J; Schneider D
Evolution of bacterial persistence to antibiotics during a 50,000-generation experiment in an antibiotic-free environment Journal Article
Antibiotics, 11 (4), pp. 451, 2022, ISSN: 2079-6382.
Abstract | Links | BibTeX | Altmetric | Tags: Correlated Responses, Genotypes and Phenotypes
@article{mathe-hubert2022,
title = {Evolution of bacterial persistence to antibiotics during a 50,000-generation experiment in an antibiotic-free environment},
author = {Hugo Mathé-Hubert and Rafika Amie and Mikaël Martin and Joël Gaffé and Dominique Schneider},
url = {https://www.mdpi.com/2079-6382/11/4/451},
doi = {10.3390/antibiotics11040451},
issn = {2079-6382},
year = {2022},
date = {2022-03-27},
urldate = {2022-03-27},
journal = {Antibiotics},
volume = {11},
number = {4},
pages = {451},
abstract = {Failure of antibiotic therapies causes >700,000 deaths yearly and involves both bacterial resistance and persistence. Persistence results in the relapse of infections by producing a tiny fraction of pathogen survivors that stay dormant during antibiotic exposure. From an evolutionary perspective, persistence is either a ‘bet-hedging strategy’ that helps to cope with stochastically changing environments or an unavoidable minimal rate of ‘cellular errors’ that lock the cells in a low activity state. Here, we analyzed the evolution of persistence over 50,000 bacterial generations in a stable environment by improving a published method that estimates the number of persister cells based on the growth of the reviving population. Our results challenged our understanding of the factors underlying persistence evolution. In one case, we observed a substantial decrease in persistence proportion, suggesting that the naturally observed persistence level is not an unavoidable minimal rate of ‘cellular errors’. However, although there was no obvious environmental stochasticity, in 11 of the 12 investigated populations, the persistence level was maintained during 50,000 bacterial generations.},
keywords = {Correlated Responses, Genotypes and Phenotypes},
pubstate = {published},
tppubtype = {article}
}
Failure of antibiotic therapies causes >700,000 deaths yearly and involves both bacterial resistance and persistence. Persistence results in the relapse of infections by producing a tiny fraction of pathogen survivors that stay dormant during antibiotic exposure. From an evolutionary perspective, persistence is either a ‘bet-hedging strategy’ that helps to cope with stochastically changing environments or an unavoidable minimal rate of ‘cellular errors’ that lock the cells in a low activity state. Here, we analyzed the evolution of persistence over 50,000 bacterial generations in a stable environment by improving a published method that estimates the number of persister cells based on the growth of the reviving population. Our results challenged our understanding of the factors underlying persistence evolution. In one case, we observed a substantial decrease in persistence proportion, suggesting that the naturally observed persistence level is not an unavoidable minimal rate of ‘cellular errors’. However, although there was no obvious environmental stochasticity, in 11 of the 12 investigated populations, the persistence level was maintained during 50,000 bacterial generations.
Jordan J A; Lenski R E; Card K J
Idiosyncratic fitness costs of ampicillin-resistant mutants derived from a long-term experiment with Escherichia coli Journal Article
Antibiotics, 11 (3), pp. 347, 2022, ISSN: 2079-6382.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments, Genome Evolution, Historical Contingency
@article{Jordan2022.02.06.479266,
title = {Idiosyncratic fitness costs of ampicillin-resistant mutants derived from a long-term experiment with \textit{Escherichia coli}},
author = {Jalin A. Jordan and Richard E. Lenski and Kyle J. Card},
url = {https://www.biorxiv.org/content/10.1101/2022.02.06.479266v1},
doi = {10.3390/antibiotics11030347},
issn = {2079-6382},
year = {2022},
date = {2022-03-13},
urldate = {2022-03-13},
journal = {Antibiotics},
volume = {11},
number = {3},
pages = {347},
publisher = {Cold Spring Harbor Laboratory},
abstract = {Antibiotic resistance is a growing concern that has prompted a renewed focus on drug discovery, stewardship, and evolutionary studies of the patterns and processes that underlie this phenomenon. A resistant strain’s competitive fitness relative to its sensitive counterparts in the absence of drug can impact its spread and persistence in both clinical and community settings. In a prior study, we examined the fitness of tetracycline-resistant clones that evolved from five different Escherichia coli genotypes, which had diverged during a long-term evolution experiment. In this study, we build on that work to examine whether ampicillin-resistant mutants are also less fit in the absence of the drug than their sensitive parents, and whether the cost of resistance is constant or variable among independently derived lines. Like the tetracycline-resistant lines, the ampicillin-resistant mutants were often less fit than their sensitive parents, with significant variation in the fitness costs among the mutants. This variation was not associated with the level of resistance conferred by the mutations, nor did it vary across the different parental backgrounds. In our earlier study, some of the variation in fitness costs associated with tetracycline resistance was explained by the effects of different mutations affecting the same cellular pathway and even the same gene. In contrast, the variance among the ampicillin-resistant mutants was associated with different sets of target genes. About half of the resistant clones suffered large fitness deficits, and their mutations impacted major outer-membrane proteins or subunits of RNA polymerases. The other mutants experienced little or no fitness costs and with, one exception, they had mutations affecting other genes and functions. Our findings underscore the importance of comparative studies on the evolution of antibiotic resistance, and they highlight the nuanced processes that shape these phenotypes.},
keywords = {Descendant Experiments, Genome Evolution, Historical Contingency},
pubstate = {published},
tppubtype = {article}
}
Antibiotic resistance is a growing concern that has prompted a renewed focus on drug discovery, stewardship, and evolutionary studies of the patterns and processes that underlie this phenomenon. A resistant strain’s competitive fitness relative to its sensitive counterparts in the absence of drug can impact its spread and persistence in both clinical and community settings. In a prior study, we examined the fitness of tetracycline-resistant clones that evolved from five different Escherichia coli genotypes, which had diverged during a long-term evolution experiment. In this study, we build on that work to examine whether ampicillin-resistant mutants are also less fit in the absence of the drug than their sensitive parents, and whether the cost of resistance is constant or variable among independently derived lines. Like the tetracycline-resistant lines, the ampicillin-resistant mutants were often less fit than their sensitive parents, with significant variation in the fitness costs among the mutants. This variation was not associated with the level of resistance conferred by the mutations, nor did it vary across the different parental backgrounds. In our earlier study, some of the variation in fitness costs associated with tetracycline resistance was explained by the effects of different mutations affecting the same cellular pathway and even the same gene. In contrast, the variance among the ampicillin-resistant mutants was associated with different sets of target genes. About half of the resistant clones suffered large fitness deficits, and their mutations impacted major outer-membrane proteins or subunits of RNA polymerases. The other mutants experienced little or no fitness costs and with, one exception, they had mutations affecting other genes and functions. Our findings underscore the importance of comparative studies on the evolution of antibiotic resistance, and they highlight the nuanced processes that shape these phenotypes.
2021
Izutsu M; Lake D M; Matson Z W D; Dodson J P; Lenski R E
Effects of periodic bottlenecks on the dynamics of adaptive evolution in microbial populations Unpublished
2021.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments, Fitness Trajectories, Theory and Simulations
@unpublished{,
title = {Effects of periodic bottlenecks on the dynamics of adaptive evolution in microbial populations},
author = {Minako Izutsu and Devin M. Lake and Zachary W. D. Matson and Jack P. Dodson and Richard E. Lenski},
doi = {10.1101/2021.12.29.474457},
year = {2021},
date = {2021-12-30},
urldate = {2021-12-30},
journal = {10.1101/2021.12.29.474457},
publisher = {LTEE},
abstract = {Population bottlenecks are common in nature, and they can impact the rate of adaptation in evolving populations. On the one hand, each bottleneck reduces the genetic variation that fuels adaptation. On the other hand, fewer founders can undergo more generations and leave more descendants in a resource-limited environment, which allows surviving beneficial mutations to spread more quickly. Here we investigate the impact of repeated bottlenecks on the dynamics of adaptation in experimental populations of Escherichia coli. We propagated 48 populations under four dilution regimes (2-, 8-, 100-, and 1000-fold), all reaching the same final size each day, for 150 days. A simple model in which adaptation is limited by the supply rate of beneficial mutations predicts that fitness gains should be maximized with ∼8-fold dilutions. The model also assumes that selection acts only on the overall growth rate and is otherwise identical across dilution regimes. However, we found that selection in the 2-fold regime was qualitatively different from the other treatments. Moreover, we observed earlier and greater fitness gains in the populations subjected to 100- and 1000-fold dilutions than in those that evolved in the 8-fold regime. We also ran simulations using parameters estimated independently from a long-term experiment using the same ancestral strain and environment. The simulations produced dynamics similar to our empirical results under these regimes, and they indicate that the simple model fails owing to the assumption that the supply of beneficial mutations limits adaptation.},
keywords = {Descendant Experiments, Fitness Trajectories, Theory and Simulations},
pubstate = {published},
tppubtype = {unpublished}
}
Population bottlenecks are common in nature, and they can impact the rate of adaptation in evolving populations. On the one hand, each bottleneck reduces the genetic variation that fuels adaptation. On the other hand, fewer founders can undergo more generations and leave more descendants in a resource-limited environment, which allows surviving beneficial mutations to spread more quickly. Here we investigate the impact of repeated bottlenecks on the dynamics of adaptation in experimental populations of Escherichia coli. We propagated 48 populations under four dilution regimes (2-, 8-, 100-, and 1000-fold), all reaching the same final size each day, for 150 days. A simple model in which adaptation is limited by the supply rate of beneficial mutations predicts that fitness gains should be maximized with ∼8-fold dilutions. The model also assumes that selection acts only on the overall growth rate and is otherwise identical across dilution regimes. However, we found that selection in the 2-fold regime was qualitatively different from the other treatments. Moreover, we observed earlier and greater fitness gains in the populations subjected to 100- and 1000-fold dilutions than in those that evolved in the 8-fold regime. We also ran simulations using parameters estimated independently from a long-term experiment using the same ancestral strain and environment. The simulations produced dynamics similar to our empirical results under these regimes, and they indicate that the simple model fails owing to the assumption that the supply of beneficial mutations limits adaptation.
Consuegra J; Gaffé J; Lenski R E; Hindré T; Barrick J E; Tenaillon O; Schneider D
Insertion-sequence-mediated mutations both promote and constrain evolvability during a long-term experiment with bacteria Journal Article
Nature Communications, 12 (1), pp. 980, 2021, ISSN: 2041-1723.
Abstract | Links | BibTeX | Altmetric | Tags: Fitness Trajectories, Genome Evolution, Mutation Rates
@article{Consuegra2021,
title = {Insertion-sequence-mediated mutations both promote and constrain evolvability during a long-term experiment with bacteria},
author = {Jessika Consuegra and Joël Gaffé and Richard E. Lenski and Thomas Hindré and Jeffrey E. Barrick and Olivier Tenaillon and Dominique Schneider},
url = {http://www.nature.com/articles/s41467-021-21210-7},
doi = {https://doi.org/10.1038/s41467-021-21210-7},
issn = {2041-1723},
year = {2021},
date = {2021-12-01},
urldate = {2021-12-01},
journal = {Nature Communications},
volume = {12},
number = {1},
pages = {980},
publisher = {Springer US},
abstract = {Insertion sequences (IS) are ubiquitous bacterial mobile genetic elements, and the mutations they cause can be deleterious, neutral, or beneficial. The long-term dynamics of IS elements and their effects on bacteria are poorly understood, including whether they are primarily genomic parasites or important drivers of adaptation by natural selection. Here, we investigate the dynamics of IS elements and their contribution to genomic evolution and fitness during a long-term experiment with \textit{Escherichia coli}. IS elements account for ~35% of the mutations that reached high frequency through 50,000 generations in those populations that retained the ancestral point-mutation rate. In mutator populations, IS-mediated mutations are only half as frequent in absolute numbers. In one population, an exceptionally high ~8-fold increase in IS 150 copy number is associated with the beneficial effects of early insertion mutations; however, this expansion later slowed down owing to reduced IS 150 activity. This population also achieves the lowest fitness, suggesting that some avenues for further adaptation are precluded by the IS 150 -mediated mutations. More generally, across all populations, we find that higher IS activity becomes detrimental to adaptation over evolutionary time. Therefore, IS-mediated mutations can both promote and constrain evolvability.},
keywords = {Fitness Trajectories, Genome Evolution, Mutation Rates},
pubstate = {published},
tppubtype = {article}
}
Insertion sequences (IS) are ubiquitous bacterial mobile genetic elements, and the mutations they cause can be deleterious, neutral, or beneficial. The long-term dynamics of IS elements and their effects on bacteria are poorly understood, including whether they are primarily genomic parasites or important drivers of adaptation by natural selection. Here, we investigate the dynamics of IS elements and their contribution to genomic evolution and fitness during a long-term experiment with Escherichia coli. IS elements account for ~35% of the mutations that reached high frequency through 50,000 generations in those populations that retained the ancestral point-mutation rate. In mutator populations, IS-mediated mutations are only half as frequent in absolute numbers. In one population, an exceptionally high ~8-fold increase in IS 150 copy number is associated with the beneficial effects of early insertion mutations; however, this expansion later slowed down owing to reduced IS 150 activity. This population also achieves the lowest fitness, suggesting that some avenues for further adaptation are precluded by the IS 150 -mediated mutations. More generally, across all populations, we find that higher IS activity becomes detrimental to adaptation over evolutionary time. Therefore, IS-mediated mutations can both promote and constrain evolvability.
Deatherage D E; Barrick J E
High-throughput characterization of mutations in genes that drive clonal evolution using multiplex adaptome capture sequencing Journal Article
Cell Systems, 12 (12), pp. 1187-1200, 2021, ISSN: 24054712.
Abstract | Links | BibTeX | Altmetric | Tags: Descendant Experiments, Fitness Trajectories, Methods and Miscellaneous
@article{DEATHERAGE2021,
title = {High-throughput characterization of mutations in genes that drive clonal evolution using multiplex adaptome capture sequencing},
author = {Daniel E. Deatherage and Jeffrey E. Barrick},
url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8678185/},
doi = {10.1016/j.cels.2021.08.011},
issn = {24054712},
year = {2021},
date = {2021-09-01},
urldate = {2021-09-01},
journal = {Cell Systems},
volume = {12},
number = {12},
pages = {1187-1200},
abstract = {Understanding how cells are likely to evolve can guide medical interventions and bioengineering efforts that must contend with unwanted mutations. The adaptome of a cell—the neighborhood of genetic changes that are most likely to drive adaptation in a given environment—can be mapped by tracking rare beneficial variants during the early stages of clonal evolution. We used multiplex adaptome capture sequencing (mAdCap-seq), a procedure that combines unique molecular identifiers and hybridization-based enrichment, to characterize mutations in eight \textit{Escherichia coli} genes known to be under selection in a laboratory environment. We tracked 301 mutations at frequencies as low as 0.01% and inferred the fitness effects of 240 of these mutations. There were distinct molecular signatures of selection on protein structure and function for the three genes with the most beneficial mutations. Our results demonstrate how mAdCap-seq can be used to deeply profile a targeted portion of a cell's adaptome.},
keywords = {Descendant Experiments, Fitness Trajectories, Methods and Miscellaneous},
pubstate = {published},
tppubtype = {article}
}
Understanding how cells are likely to evolve can guide medical interventions and bioengineering efforts that must contend with unwanted mutations. The adaptome of a cell—the neighborhood of genetic changes that are most likely to drive adaptation in a given environment—can be mapped by tracking rare beneficial variants during the early stages of clonal evolution. We used multiplex adaptome capture sequencing (mAdCap-seq), a procedure that combines unique molecular identifiers and hybridization-based enrichment, to characterize mutations in eight Escherichia coli genes known to be under selection in a laboratory environment. We tracked 301 mutations at frequencies as low as 0.01% and inferred the fitness effects of 240 of these mutations. There were distinct molecular signatures of selection on protein structure and function for the three genes with the most beneficial mutations. Our results demonstrate how mAdCap-seq can be used to deeply profile a targeted portion of a cell's adaptome.
van Raay K; Stolyar S; Sevigny J; Draghi J; Lenski R E; Marx C J; Kerr B; Zaman L
Evolution with private resources reverses some changes from long-term evolution with public resources Unpublished
bioRxiv, 2021.
Abstract | Links | BibTeX | Altmetric | Tags: Cell Morphology, Correlated Responses, Demography and Ecology, Descendant Experiments, Genotypes and Phenotypes, Historical Contingency, Methods and Miscellaneous
@unpublished{Raay2021,
title = {Evolution with private resources reverses some changes from long-term evolution with public resources},
author = {Katrina {van Raay} and Sergey Stolyar and Jordana Sevigny and Jeremy Draghi and Richard E. Lenski and Christopher J. Marx and Benjamin Kerr and Luis Zaman},
url = {https://www.biorxiv.org/content/10.1101/2021.07.11.451942v1},
doi = {https://doi.org/10.1101/2021.07.11.451942},
year = {2021},
date = {2021-07-12},
urldate = {2021-07-12},
journal = {bioRxiv},
pages = {2021.07.11.451942},
abstract = {A population under selection to improve one trait may evolve a sub-optimal state for another trait due to tradeoffs and other evolutionary constraints. How this evolution affects the capacity of a population to adapt when conditions change to favor the second trait is an open question. We investigated this question using isolates from a lineage spanning 60,000 generations of the Long-Term Evolution Experiment (LTEE) with \textit{Escherichia coli}, where cells have access to a shared pool of resources, and have evolved increased competitive ability and a concomitant reduction in numerical yield. Using media-in oil emulsions we shifted the focus of selection to numerical yield, where cells grew in isolated patches with private resources. We found that the time spent evolving under shared resources did not affect the ability to re-evolve toward higher numerical yield. The evolution of numerical yield commonly occurred through mutations in the phosphoenolpyruvate phosphotransferase system. These mutants exhibit slower uptake of glucose, making them poorer competitors for public resources, and produce smaller cells that release less carbon as overflow metabolites. Our results demonstrate that mutations that were not part of adaptation under one selective regime may enable access to ancestral phenotypes when selection changes to favor evolutionary reversion. },
howpublished = {bioRxiv},
keywords = {Cell Morphology, Correlated Responses, Demography and Ecology, Descendant Experiments, Genotypes and Phenotypes, Historical Contingency, Methods and Miscellaneous},
pubstate = {published},
tppubtype = {unpublished}
}
A population under selection to improve one trait may evolve a sub-optimal state for another trait due to tradeoffs and other evolutionary constraints. How this evolution affects the capacity of a population to adapt when conditions change to favor the second trait is an open question. We investigated this question using isolates from a lineage spanning 60,000 generations of the Long-Term Evolution Experiment (LTEE) with Escherichia coli, where cells have access to a shared pool of resources, and have evolved increased competitive ability and a concomitant reduction in numerical yield. Using media-in oil emulsions we shifted the focus of selection to numerical yield, where cells grew in isolated patches with private resources. We found that the time spent evolving under shared resources did not affect the ability to re-evolve toward higher numerical yield. The evolution of numerical yield commonly occurred through mutations in the phosphoenolpyruvate phosphotransferase system. These mutants exhibit slower uptake of glucose, making them poorer competitors for public resources, and produce smaller cells that release less carbon as overflow metabolites. Our results demonstrate that mutations that were not part of adaptation under one selective regime may enable access to ancestral phenotypes when selection changes to favor evolutionary reversion.