Studies with the Cellulolytic Fraction of Rumen Bacteria Obtained by Differential Centrifugation

Abstract

Suspensions of bovine and ovine rumen bacteria were separated into several different fractions by means of differential centrifugation. That fraction of bacteria still in suspension at 1500 x G but sedimented at 3000 x G was found to contain the majority of the cellulolytic rumen bacteria. This fraction contained only 21% of the TCA insoluble nitrogen (bacterial protein) found in the whole suspension of rumen micro-organisms. Photomicrographs are shown of the bacteria in the various fractions. Fermentation studies with the 3000 x G sediment showed that after incubation with cellulose as the sole carbohydrate source, a predominance of Gram-negative micrococci were present along with a lesser number of very small Gram-negative rods. These observations indicate that the Gram-negative micrococci are the principal cellulose-digesting organisms which proliferate in vitro. These same organisms were also found in large numbers in the inoculum obtained from the rumen. Incubation of the 3000 x G sediment with cellulose as the sole carbohydrate substrate resulted in the formation of large amounts of acetic and propionic acid, a lesser amount of succinic acid and traces of butyric and higher acids. The microorganisms showed a strict requirement for both valeric acid and biotin. Further studies showed that the fatty acid requirement could be satisfied by valeric acid, and that a branched-chain acid was not required. Copyright © . .