Engineering Emergent Properties in Synthetic Microbial Communities

Authors: 
Bernstein, H. C., Pacific Northwest National Laboratory
Beliaev, A. S., Pacific Northwest National Laboratory
Fredrickson, J. K., Pacific Northwest National Laboratory

Traditionally, engineers and synthetic biologists exert control over microbial metabolism by adding or removing genes and pathways from a single host. However, new paradigms have been realized though the ‘consortia’ concept of engineering and compartmenting metabolic function within assigned community members. Beneficial emergent properties, such as enhanced productivity and/or stability, can be engineered into synthetic or thoughtfully constructed microbial communities. This presentation focuses on how emergent properties have been realized from community-engineering. Binary consortia were either metabolically engineered (via genome reduction) or naturally prone to cooperate in a ‘producer-consumer’ motif.  These systems ranged from synthetic Escherichia coli co-cultures engineered for mutualistic exchange-detoxification of acetic acid to artificial wild-type assemblies of phototrophic cyanobacteria and heterotrophic counter parts. These distinct binary cultures demonstrated enhanced biomass productivity and resistance to metabolite feed-back inhibition. For example, the effect of oxygen availability on metabolically engineered E. coli systems was found to be a controlling factor for acetic acid exchange and subsequent phenotype-specific spatial patterning in biofilms and biomass productivity in chemostats. Similarly, oxygen gradients were imposed on a constructed consortium consisting of wild-type photoautotroph (Thermosynechococcus elongatus) and chemoheterotroph (Meiothermus ruber), which responded with an increased resistance to the growth inhibition effect of high oxygen-tension. This research lends critical insight to a grand-challenge for biological engineers and synthetic biologists aiming to capitalize on knowledge gained from model systems and phenomenological observation to rationally design microbial communities for controllable outputs.