Changes in Oxidation Reduction Potentials and Volatile Fatty Acid Production by Rumen Bacteria When Methane Synthesis is Inhibited

Abstract

Rumen inoculum was cultured in specially designed fermenters that allowed simultaneous measurement of pH, oxidation-reduction potentials, and gas production. The cultures were maintained at pH 6.8 by addition of 1 M NaHCO3 and continuous infusion of artificial saliva. Gas flow was maintained at 20.0 ml/min with a stream of O2-free N2. Monensin at 7.0μ/ml inhibited CH4 production 49% below control concentrations. The sodium salt of 2-bromoethanesulfonic acid added at an initial concentration of 5×10−5M inhibited CH4 production by 86% and increased H2 production from<.5μmol/min in the control to 24.5μmol/min in the inhibited fermenter. The redox potentials in the control fermenter remained above −.20V and did not change with the addition of monensin. Bromoethanesulfonic acid rapidly decreased the redox potential in the fermenter to −.33V. Volatile fatty acid production was not significantly altered by the addition of 2-bromo-ethane sulfonic acid. The addition of monensin gave the expected decrease in acetate:propionate ratios, decreased acetate and butyrate production, and increased valerate (but not propionate) production.