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

• Published in: Applied microbiology and biotechnology Vol. 100; no. 8; pp. 3389 - 3398
• Main Authors: Weimer, Paul J, Kohn, Richard A
• Format: Journal Article Book Review
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2016; Springer; Springer Nature B.V
• Subjects: alkanes; anaerobic digesters; Anaerobic digestion; Analysis; Animals; bacteria; Bacteria - classification; Bacteria - isolation & purification; Bacteria - metabolism; Biodiesel fuels; Biofuels; Biofuels - analysis; Biomass; Biomedical and Life Sciences; Biosynthesis; Biotechnology; Carbohydrates; Chemical properties; Chemical reactions; Chemical reactors; Clostridium; Clostridium kluyveri; Energy; Ethanol; Fatty acids; Fatty Acids, Volatile - analysis; Fatty Acids, Volatile - metabolism; Fermentation; Fuels; hexanoic acid; Identification and classification; Life Sciences; Megasphaera elsdenii; methane production; methanogens; Microbial colonies; microbial communities; Microbial Genetics and Genomics; Microbiology; microbiome; Microbiota; Microorganisms; Mini-Review; mixed culture; Observations; Oxidation; Plant biomass; Raw materials; Rumen - microbiology; rumen microorganisms; Ruminantia; ruminants; Ruminants - microbiology; Sediments; Species diversity; Studies; thermodynamics; Rumen; Carboxylate platform; Reactor microbiomes; Biofuels; Reverse β-oxidation
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-016-7358-2

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 extraruminal cultivation, this mixed microbial community is a particularly accomplished practitioner of the carboxylate platform for producing fuels 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 β-oxidizing bacteria (e.g., Clostridium kluyveri or Megasphaera elsdenii) that facilitate production of valeric and caproic acids. Application of fundamental principles of thermodynamics allows 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.