The Lenski Long-Term Evolution Experiment

Arabinose Marker

REL606 and REL607 (the ancestral strains of the E. coli long-term evolution experiment) 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 at this amino acid are also known to confer an Ara+ phenotype.

Strain	Phenotype	Color	araA allele
REL606	Ara-	Pink (Red)	92D (GAC)
REL607	Ara+	White	92G (GGC)
other revertants	Ara+	White	92A (GCC)

Color of colonies when grown on tetrazolium arabinose (TA) plates.

Summary of the Known Idiosyncrasies of Each Long-Term Line

After more than 20 years and 50,000 generations of evolution in the laboratory, the various experimental replicates of the long-term experiment have diverged markedly. Some fail to grow on certain growth media.

Line	Growth	Other 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
Ara-4	Normal
Ara-5	Normal
Ara-6	Normal
Ara+1	Normal
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).