OEB 192 – 10.11.01

Genetic & physiological basis of adaptation

(Goddard et al., 2005. Nature)

(Cooper, 2007. PLoS Biol.)

(Chou et al., 2009. PLoS Genetics)

• Was metal availability a stress?• Yes – and insertion was beneficial

• What effect did IS have?• Generated hybrid promoter• Increased icuAB mRNA by over

20-fold

TonB-dependent outer membrane

transporter

Periplasmic binding protein

IS insertion upstream of metal transporter

(Chou et al., 2009. PLoS Genetics)

• How could we be so bad at making media?• Noted trace metal mix changed

color with light…• Light exposure increased rate and

eliminated advantage

• Increased dosage of trace metals also increased growth

• Which metal?• 4 of 7 metals stimulated growth…

Basis of metal limitation

• EDTA nearly 100% chelating• EDTA is light-sensitive• Each metal affects chelation of all

• Answer: Cobalt• Only one which limits growth in EDTA-

free media• Gives advantage for mutant

(Chou et al., 2009. PLoS Genetics)

Incredible genetic parallelism• Examined isolates from all experiments in the lab…

• 0/8 S-evolved populations had icuAB mutation• 30/32 evolved with M had new icuAB allele• All were ISMex4, into only 2 sites

• Large advantage, 3 possible reasons for high rate:

ISMex4

~10 kb

icuA icuB

Target sequence 2o structureLocal hopping

(Chou et al., 2009. PLoS Genetics)

Physiological basis of fitness advantage• Evolved icuAB allele only

an advantage on C1 or C2 compounds• In common: glyoxylate

regeneration pathway• Two vitamin B12-requiring

reactions (has Co)

• Glyoxylate or cobalamin stimulated wild-type in MP media

• Later Co-limitation independently discovered via metabolomics (Keifer et al., 2009. PLoS One)

Wednesday (11/3): Fitness & optimality