February 11 2015

12:00 LSB 2320

Brandon Gaut
Ecology & Evolutionary Biology, UC Irvine

Connections among Genotype, Phenotype and Fitness in E. coli High Temperature Lines Connections among Genotype, Phenotype and Fitness in E. coli High Temperature Lines


To estimate the number and diversity of beneficial mutations, we experimentally evolved 115 populations of Escherichia coli to 42.2°C for 2000 generations and sequenced one genome from each population. We identified 1331 total mutations, affecting more than 600 different sites. Few mutations were shared among replicates, but a strong pattern of convergence emerged at the level of genes, operons, and functional complexes. We inferred the pervasive presence of epistasis among beneficial mutations, which shaped adaptive trajectories into at least two distinct pathways involving mutations either in the RNA polymerase complex or the termination factor rho. We have found that these two adaptive pathways differ with respect to phenotype, particularly with respect to trade-offs with temperature niche. All 115 clones shifted their upper boundary to at least 45 °C. Roughly half increased their lower niche boundary concomitantly, representing a shift of thermal niche, but the expanded their thermal niche. We associated these niche dynamics with genotypes and confirmed associations by engineering single mutations in the rpoB gene, which encodes the beta subunit of RNA polymerase, and the rho gene, which encodes a termination factor. Our work has not only identified two different genetic pathways toward high-temperature adaptation but also shown that they have contrasting effects with respect to thermal tradeoffs.















































































































































































































































































































































































































































































































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