Why Doesn’t Everyone Do Everything? the Cooperation Conundrum of Engineered Consortia for the Catabolism of Phosphotriester Pesticides

The microbial catabolism of recently introduced xenobiotics, such as phosphotriester pesticides, has evolved both in individual strains (monocultures) and in mixed consortia (cocultures). These two types of phosphotriester catabolism represent two distinct metabolic strategies found in nature: monocultures, where one organism fully catabolizes the phosphotriester, and cocultures, where catabolic genes are distributed across organisms in the same environment. While monocultures represent the predominant and most studied bioprocess engineering strategy today, cocultures are rarely studied. Furthermore, the reasons why naturally evolved metabolic pathways are distributed in co-cultures are poorly understood. Knowing what factors favor the evolution of a catabolic monoculture vs. coculture can elucidate the benefit of each metabolic engineering strategy for use in bioprocess engineering. We engineer E. coli to degrade phosphotriesters in order to study the evolution of catabolic pathways. To grow on phosphotriesters as the sole phosphorous source, E. coli requires a triesterase and a diesterase enzyme. We distribute this two-enzyme catabolic pathway to simulate a monoculture and a coculture catabolic strategy. The two strategies will be grown separately, as well as together in competition, to assay the viability of monocultures and cocultures. We hypothesize that (i) the bioenergetic cost of the pathway, manipulated via induction of enzyme expression; (ii) the availability of the substrate; and (iii) its physiological coupling to fitness, influence the viability of both strategies. These variables can lead to the competitive exclusion of either strategy, or coexistence of both.