In Vitro Studies on Methanogenic Rumen Bacteria. II. Fermentation of Butyric and Valeric Acid

Abstract

Summary Stabilized enrichment cultures which produced methane from butyric and valeric acids were readily obtained from bovine rumen fluid. All attempts to obtain methanogenic enrichment cultures which convert propionic acid to methane were unsuccessful. Butyric acid was completely oxidized to methane and carbon dioxide. The oxidation of valeric acid was not carried to completion, and in such cultures the propionic acid from the oxidation of valeric acid, coupled with the reduction of carbon dioxide, accumulated in the fermentation medium as an end product. The acetic acid from the oxidation of butyric and valeric acid, coupled with the reduction of carbon dioxide, was readily dissimilated by the cultures. The rate of acetate utilization was equal to or greater than the rate of butyrate and valerate oxidation. The presence of methane bacteria in rumen fluid, which biochemically are closely related to Methanobacterium suboxydans , suggests that butyric and valeric acids are the reductants, with carbon dioxide the oxidant as an additional pathway of in vivo formation of rumen methane.