Seminars

Comparative genome sequencing previously identified specific adaptive mutations during Escherichia coli (E. coli) adaptation for fast growth on glycerol. However, like most existing adaptive evolution studies, the specific molecular mechanism by which mutations provide growth benefits are not well characterized. Here, using a combination of metabolomics and proteomics we show that strains carrying mutations derived from adaptation for fast growth on glycerol use distinct metabolic strategies to gain a growth advantage. First, a 27 bp deletion in the rpoC gene increases metabolic efficiency for biomass production, by drastically affecting redox balance, reduces a costly post-synthetic lipid modification process, and generally results in lower levels of multiple intracellular metabolites. Second, a point mutation in the glpK gene promotes growth by increasing glycerol uptake rate and access to metabolizable carbon but results in increased carbon wasting in the form of overflow. In a strain carrying both mutations, these seemingly contrasting carbon and energy saving and wasting mechanisms work synergistically to produce an 89% increase in growth rate compared to the wild type. The adaptive mechanisms shown in this study provide some of the first insight into metabolic reprograming during adaptive evolution and help connect specific mutations with the metabolic phenotype. Moreover the results of our study highlight some of the metabolic trade-offs connected with the cellular economics of fast growth.