Effects of Various Methane Inhibitors on the Fermentation of Amino Acids by Mixed Rumen Microorganisms in Vitro

Abstract

Monensin (2 ppm), lasalocid (2 ppm), chloroform (4 × 10−5 M) and carbon monoxide (.5 atm) inhibited the production of CH4 by mixed rumen bacteria that were incubated with an excess of protein hydrolyzate (Trypticase, 15 g/liter). All four CH4 inhibitors reduced amino acid deamination, but the degree of CH4 inhibition was not related to NH3 accumulation. Chloroform almost completely eliminated CH4 production and reduced NH3 production by 10%. Ionophores, monensin and lasalocid, inhibited CH4 by 51 and 44%, and decreased NH3 more than 50%. Carbon monoxide inhibited CH4 and NH3 production by 89 and 20%. All four CH4 inhibitors decreased amino acid fermentation, but the mechanisms were different. With chloroform some H2 accumulated in the incubation vessels, and the ratio of straight-chain to branched-chain VFA was not different (>.05) from controls. Carbon monoxide, a specific bacterial hydrogenase inhibitor, caused a large increase (<.05) in the ratio of straight-chain to branched-chain acids. This increase resulted from a selective inhibition of branched-chain amino acid fermentation. The ionophores also decreased isovalerate and 2-methyl butyrate formation, but the straight-chain to branched-chain ratio decreased. This reduction resulted from a more pronounced decrease in acetate. Most of the decrease in NH3 production due to ionophores was explained by a decrease in microbial protein. Comparison of carbon monoxide and iono-phore treatments indicated that the action of monensin and lasalocid cannot be solely explained by a simple inhibition of hydrogenase activity.