Crib Sheet

This page collects some useful information related to studying the LTEE.

Arabinose Marker

REL606 and REL607 (the ancestral strains of the E. coli LTEE) differ by a single point mutation in the araA gene. This mutation was originally present in REL606. It makes an excellent neutral marker for evolution and competition experiments. REL607 was selected as a spontaneous arabinose-utilizing revertant from REL607. Most spontaneous revertants selected from a strain with the REL606 araA allele have the REL607 allele, but other mutations this codon to other amino acids are also known to confer an Ara+ phenotype.

Strain	Phenotype	Color	araA alelle (codon)
REL606	Ara–	🔴 Red	92D (GAC)
REL607	Ara+	◯ White	92G (GGC)
Other revertants	Ara+	◯ White	92A (GCC)

Summary of Each Long-Term Line

After decades and tens of thousands of generations of evolution in the laboratory, E. coli cells in the different populations of the long-term experiment have diverged markedly in some of their characteristics. Some fail to grow on certain agar growth media. Many evolved elevated mutation rates (hypermutability).

Line	Agar Plate Growth Notes	Notes
Ara–1 🔴	Normal
Ara–2 🔴	≥20k some colonies fail to grow on MA, MG, and TA. Normal growth on LB.	Stable Polymorphism
Ara–3 🔴	Normal	Citrate Utilization
Ara–4 🔴	Normal
Ara–5 🔴	Normal
Ara–6 🔴	Normal
Ara+1 ◯	Normal	IS Element Mutator
Ara+2 ◯	Normal
Ara+3 ◯	Normal
Ara+4 ◯	Normal
Ara+5 ◯	Normal
Ara+6 ◯	≥10k unreliable growth on TA and LB, no growth on MA. Normal growth on MG.

Key to Media: minimal arabinose (MA), minimal glucose (MG), tetrazolium arabinose (TA).

Cell Density

Density of E. coli cells in DM media with different concentrations of glucose (DM1000 = 1000 µg/L). Evolved strains achieve roughly half the number of colony-forming units (CFU) because their cells are larger.

DM glucose	Ancestor density (cells/ml)	Evolved density (cells/ml)
DM10	2×107	1×107
DM25	5×107	2.5×107
DM50	1×108	5×107
DM100	2×108	1×108
DM250	5×108	2.5×108
DM500	1×109	5×108
DM1000	2×109	1×109
DM2000	4×109	2×109