Fermentation of Cellulose with a Mixed Microbial Rumen Culture with and without Methanogenesis

Abstract

Ruminal fermentation has been well studied and includes cellulolytic microorganisms to hydrolyze cellulose to monomers, acidogenic microbes including cellulolytic microorganism to convert the monomers to volatile fatty acids (VFA), hydrogen and carbon dioxide and methanogens to convert the acetic acid, hydrogen and carbon dioxide to methane. Notably, methane production in ruminants causes energy loss for the animal and emitted methane contributes significantly to greenhouse gases in the atmosphere. The present study focuses on selectively inhibiting of the methanogens using 2–bromoethanesulfonate (BES) and its effect on ruminal fermentation in an anaerobic rumen bioreactor model system. It was found that BES inhibited methane production (99.7%) and that addition of BES decreased the total VFA productivity from 3 g/L/day to 1.3 g/L/day. Our study also found that addition of BES not only inhibited the methanogens, but also had an impact on the non-methanogenic bacteria as well, resulting in a decrease in the acetic acid productivity from 1.8 g/L/day, in a reactor without BES to 0.8 g/L/day in reactor with BES added. Endoglucanase assay revealed that addition of BES further inhibits cellulolytic microbes, resulting in a decrease in endoglucanase concentration in the reactor supplemented with BES. A notable increase in hydrogen partial pressure was seen in the reactor with BES (from 1.7% to 29.8%).