Clonal populations of microbes are employed in the majority of microbial bioprocesses. This approach has inherent limitations, such as the effect of complex non-native pathways on metabolic load that can result in low productivity. Community-based bioprocessing has the potential to address such limitations through a division of labor approach. The division of a bioprocess within a community could be designed such that discordant or rate-limiting reactions occur in separate hosts. Additionally, hosts optimized for a specific set of reactions, or pathways, could be used as modular components for different or more complex processes. There are challenges associated with constructing synthetic microbial communities. One of these challenges is engineering consortia with defined, predictable community composition. To address this challenge we used cell-cell communication to engineer synthetic commensalism, where one species depends on another for survival, between Gram-negative Escherichia coli and Gram-positive Bacillus megaterium. In this system the growth of E. coli is controlled by its response to a quorum sensing signal molecule, acyl-homoserine lactone (AHL), produced by B. megaterium. AHL rescues E. coli by inducing production of an essential metabolite necessary for growth. We observed AHL-dependent growth in E. coli using two engineered rescue strains, a tryptophan auxotroph and a tyrosine auxotroph, when grown with AHL-producing B. megaterium. While the communication-based rescue system functioned as desired, we observed B. megaterium cell death in co-culture conditions where E. coli thrived. Altering the culture conditions by switching from batch to fed-batch culture or improving mixing was found to stabilize community composition. We will also describe ongoing work characterizing the behavior and stability of our commensal co-culture pairs in continuous culture.

Cooperation in a synthetic microbial community through engineered commensalism

251st National Meeting (2016)

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