Evolution of Cross-Feeding in a Simple Bacterial Community: Genetic Determinants

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Alexander, Ashley Marie
Rosenzweig, Frank
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Syntrophic interactions, like cross-feeding, are ubiquitous in the microbial world and occur between different species and between different ecotypes of the same species. We seek to understand the conditions that favor intraspecific syntrophy using experimental evolution. Previous experiments led us to hypothesize that a limited number of mutations, perhaps only two, favor the emergence of cross-feeding lineages from a single ancestral clone. These mutations result in the overproduction of, and restricted access to, overflow metabolites. To test this hypothesis, we used site-directed mutagenesis to introduce the two mutations into an otherwise wild-type Escherichia coli strain, K12 MG1655. This genetically engineered strain was then evolved under glucose limitation as was done in previous studies where cross-feeding was observed. The resulting experimental populations are currently being analyzed for the emergence of inter-clonal cross-feeding. The discoveries made possible by pursuing this line of inquiry promise to enhance our understanding of how metabolically complex communities emerged early on in the history of life on Earth and illuminate why certain mutational trajectories are followed in polymorphic diseases like cancer.
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