(674e) Engineered Biofilms for Isobutanol Production: In silico Modeling of a Two-Species Bacterial Community

Most efforts to engineer microbial consortia for biotechnological applications have focused on well mixed systems. For example, well-mixed microbial communities offer the potential to achieve consolidated bioprocessing (CBP) of soluble lignocellulosic materials where different microbes are responsible for biomass degradation, conversion of the released sugars to desired products and consumption of toxic metabolic byproducts. In nature, the majority of microbes grow as biofilms in diverse communities to compete for and efficiently utilize available nutrients. While considerable progress towards engineering synthetic communities has been realized, existing approaches are largely based on well mixed planktonic cultures which fundamentally lack the three-dimensional structure of naturally occurring microbial biofilms. We believe that engineered biofilm communities hold great promise for diverse applications including biofuels production.

Our long-term goal is to engineer a biofilm community for conversion of cellulose to the second generation liquid fuel isobutanol. As a first step towards this goal, we have developed a biofilm metabolic model of a two-species system comprised of the facultative sugar utilizer Escherichia coli engineered for aerobic isobutanol synthesis and the anaerobic organic acid oxidizer/iron(III) reducer Geobacter metallireducens. Glucose and oxygen are supplied at the top of the biofilm to support E. coli growth and isobutanol synthesis. Organic acids and iron(III) are supplied at the bottom of the biofilm to support Geobacter metallireducens growth and mimic organic acid (acetate, ethanol) synthesis by unmodeled cellulose degraders. Our model predicts that the two species will spatially organize along gradients of the electron donors and acceptors. E. coli located in the aerobic region synthesizes isobutanol and acetate, which diffuses into anaerobic region where the acetate is consumed by G. metallireducens. We predict that the E. coli-G. metallireducens biofilm community will produce higher levels of isobutanol than E. coli alone due to G. metallireducens detoxification of environment. This result holds even when G. metallireducens only consumes acetate produced by E. coli, suggesting that the two species biofilm community may serve as a modular platform for development of more complex biofuel producing systems.