Lignocellulose, or plant biomass, is a highly prevalent, renewable carbon source with great potential for industrial applications, such as commodity chemical production, yet it is challenging to utilize given its resistance to degradation. Plants have evolved to curb breakdown caused by microbes, and a very limited number of microbes have been shown to degrade lignocellulose. Individual microbial strains have been engineered to convert lignocellulose to value-added products, but metabolic burden hinders these processes as individual strains are expected to perform several laborious tasks, which often results in low product generation. However, microbial communities provide means to limit the metabolic burden associated with each member via division of labor. Lignocellulose is naturally and efficiently broken down in the guts of large herbivores by a community of microbes. Anaerobic fungi are at the forefront of this process because they secrete an extensive collection of carbohydrate active enzymes that help degrade the lignocellulosic biomass. In the guts of large herbivores, methanogens utilize fermentation products from the anaerobic fungi to make methane, and chain-elongating bacteria convert fungal products to volatile fatty acids (VFAs). VFAs are far more valuable than methane, and limiting methanogen growth or excluding them completely provides means to drive the metabolic processes towards the generation of VFAs. Metagenomic and metatranscriptomic findings for natural microbial consortia have provided insight for the major bacterial players involved in chain elongation in the rumen. By applying this increased understanding, we have selected microbial members to pair with anaerobic fungi in synthetic communities to convert lignocellulose to value-added products. This marks major progress towards consolidated bioprocessing, as the entire system is fully anaerobic and defined, and this effort helps elucidate mechanisms to engineer and profit from microbial consortia based on natural microbial processes.

Engineering microbial consortia for bioproduct generation

ACS Spring 2022

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