Fitness of Escherichia coli when in Mixed Culture with Enterococcus faecalis
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Escherichia coli (E. coli) coexists with many different species, such as Enterococcus faecalis (E. faecalis), in the gastrointestinal tract of many animals. Under normal circumstances, the two bacteria live alongside each other and a multitude of other microorganisms without causing infection. However, there are occasional instances when an imbalance occurs and certain flora are able to outcompete the rest. These superior bacteria express specific traits that allow them to increase colonization and infect the host organism. There is currently little known about the mechanism of how E. coli is able coexist with E. faecalis. Using the Keio collection of E. coli, we identified that the gene yliK in E. coli, commonly known as methylmalonoyl CoA mutase, that is essential for its growth when in mixed culture with E. faecalis. Methylmalonoyl CoA mutase is part of a four gene operon encoding for enzymes that convert succinate into propionate. The E. coli mutant pure culture exhibited increased fitness with the addition of propionate. The E. faecalis, although at a much lower cell density, also exhibited increased fitness with the addition of propionate. The E. coli mutant sbm/E. faecalis mixed culture showed to have increased fitness when grown together as when compared to the fitness of the two bacteria in pure culture. The E. coli mutant sbm/E. faecalis mixed culture also showed an increase in fitness with the addition of propionate. These results suggest that E. coli and E. faecalis increase the other’s fitness, and that this elevated fitness is enhanced when propionate is added to the environment.