ADDING VALUE TO BIOFUELS PRODUCTION SYSTEMS BASED ON PERENNIAL FORAGES
Location: Cell Wall Biology and Utilization Research
Title: Quantitative analysis of growth and volatile fatty acid production by the anaerobic ruminal bacterium Megasphaera elsdenii
Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2012
Publication Date: April 17, 2013
Citation: Weimer, P.J., Moen, G.N. 2013. Quantitative analysis of growth and volatile fatty acid production by the anaerobic ruminal bacterium Megasphaera elsdenii. Applied Microbiology and Biotechnology. 97:4075-4081.
Interpretive Summary: Megasphaera elsdenii is an anaerobic bacterium from the cow rumen that can ferment both glucose and lactic acid to produce organic acids that can be chemically converted to liquid fuels or to propane. We found that both glucose and lactic acid supported growth at similar rates, but lactic acid was fermented much more efficiently and produced a higher yield of organic acids. Because lactic acid is readily produced from sugar fermentations by many organisms, a mixed culture containing Megasphaera elsdenii can provide a potential route to economical biofuels production. This research will be useful to researchers who are developing new sustainable bioenergy processes.
Megaspheara elsdenii T81 grew on either DL-lactate or D-glucose at similar rates (0.85 per h), but displayed major differences in the fermentation of these substrates. Lactate was fermented at up to 210-mM concentration to yield acetic, propionic, butyric, and valeric acids. The bacterium was able to grow at much higher concentrations of D-glucose (500 mM), but never removed more than 80 mM of glucose from the medium. Nearly 60% of the glucose removed was sequestered as intracellular glycogen, with low yields of even-carbon acids (acetate, butyrate, caproate). In the presence of both substrates, glucose was not used until lactate was nearly exhausted, even by cells pregrown on glucose. Glucose-grown cultures maintained only low extracellular concentrations of acetate, and addition of exogenous acetate increased yields of butyrate, but not caproate. By contrast, exogenous acetate had little effect on lactate fermentation. At pH 6.5, growth rate was halved by exogenous addition of 60 mM propionate, 69 mM butyrate, 44 mM valerate, or 25 mM caproate. The results were consistent with this species’ role as an effective ruminal lactate consumer. They suggest that this organism may be useful for industrial production of volatile fatty acids from lactate, or from glucose, if exogenous acetate is supplied, and product tolerance can be improved.