Impacts of ruminal microorganisms on the production of fuels: how can we intercede from the outside?

Authors: Weimer, Paul; KOHN, RICHARD - University Of Maryland

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2016
Publication Date: 2/16/2016
Publication URL: http://handle.nal.usda.gov/10113/62657
Citation: Weimer, P.J., Kohn, R.A. 2016. Impacts of ruminal microorganisms on the production of fuels: how can we intercede from the outside? Applied Microbiology and Biotechnology. 100:3389–3398.

Interpretive Summary: The same properties that make the rumen microbial community ideal for converting forages to nutrients for the host animal also make this community a promising agent for industrial production of volatile fatty acids that can be used to produce fuels and chemicals. In particular, the rumen community can be easily and stably maintained in bioreactors fed a variety of biomass materials. By augmenting the fermentation with waste streams containing ethanol or lactic acid, the community can produce two particularly valuable commodities, valeric and caproic acids, that can be easily converted to liquid fuels. Strategies are presented here to improve the yields of these compounds, and to further produce other, unexpected fuel compounds. The information will be useful to engineers to develop sustainable, low-input biofuel technologies.

Technical Abstract: The ruminal microbiome rapidly converts plant biomass to short-chain fatty acids (SCFA) that nourish the ruminant animal host. Because of its high species diversity, functional redundancy, and ease of in vitro (extraruminal) cultivation, this mixed microbial community can be regarded as a particularly accomplished practitioner of the carboxylate platform for producing fuel and chemical precursors. Unlike reactor microbiomes derived from anaerobic digesters or sediments, the ruminal community naturally produces high concentrations of SCFA, with only modest methane production owing to the absence of both proton-reducing acetogens and aceticlastic methanogens. The extraruminal fermentation can be improved by addition of ethanol or lactate product streams, particularly in concert with reverse beta-oxidizing bacteria (Clostridium kluyeri or Megasphaera elsdenii) that facilitate production of valeric and caproic acids. Application of fundmental principles of thermodynamics allows for identification of optimal conditions for SCFA chain elongation, as well as discovery of novel synthetic capabilities (e.g., medium-chain alcohol and alkane production) by this mixed culture system.