In Vivo Evolution of Escherichia Coli Pyruvate Kinase Type I: How Does Genotypic Evolution Affect Phenotype?

The adaptation of organisms and the divergence of populations and species are two important problems in microbial ecology. To study the nature of phenotypic and genotypic changes responsible for competitive fitness, Lenski and colleagues evolved 12 lines of E. coli in a fixed environment for about 40,000 generations (Lenski 1991). Unsurprisingly, they found that the 12 lines gained overall fitness when competed against the ancestor (Lenski & Travisano 1994). However, genome sequencing found at least one non-synonymous mutation in the enzyme pyruvate kinase type 1 (PK1) in all 12 populations (Cooper et al 2003). What role do these mutations play in the fitness of the evolving cell lines? PK1 is an essential glycolytic enzyme necessary for regulation of pathway flux. PK1 has been extensively studied, with its structure solved by macromolecular crystallography and the biochemical properties well characterized. In this study we investigate the structure-function relationship of the evolved PKF enzymes, using a variety of different methods, in an attempt to disentangle the phenotypic changes, and hence the underlying genotypic changes that lead to adaptation of the evolving cell lines.