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Studies with the Cellulolytic Fraction of Rumen Bacteria Obtained by Differential Centrifugation^{1, 2,}

Ohio Agricultural Experiment Station⁴, Wooster

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.

¹ Approved for publication as Journal Article No. 86-59 by the Associate Director of the Ohio Agriculture Experiment Station. A report of this work presented at the annual meeting of the American Society of Animal Production,November 27 28,1959.

² This work was supported in part by funds allocated to the Station on the recommendation of the North Central Technical Committee on Factors Affecting Utilization of Feed by Ruminants NC-25).

³ On leave from the Faculty of Agriculture, University of Alexandria, Alexandria, Egypt.

⁴ Department of Animal Science.