Characterization of Several Bovine Rumen Bacteria

DEHORITY, B. A. (Ohio Agricultural Research and Development Center, Wooster). Characterization of several bovine rumen bacteria isolated with a xylan medium. J. Bacteriol. 91:1724-1729. 1966.-Studies were conducted to characterize eight strains of bacteria isolated from bovine rumen contents, by use of a medium containing xylan as the only added carbohydrate source. Based on morphology, biochemical reactions, nutritional requirements, and fermentation products, five of the eight strains were identified as Butyrivibrio fibrisolvens. Many properties of the remaining three strains resembled Bacteroides ruminicola; however, propionic acid was consistently found as a fermentation product. When the type strains for B. ruminicola subsp. ruminicola and B. ruminicola subsp. brevis were compared with the present isolates, it was found that propionic acid was a normal fermentation product for the type strain B. ruminicola subsp. ruminicola when grown in a 40% rumen fluid-0.5 % glucose broth. Production of propionic acid was markedly reduced for all strains when grown in a 20% rumen fluid-I % glucose broth. The three remaining strains were thus placed in the species B. ruminicola, and further classified into the subspecies ruminicola (one strain) and brevis (two strains) on the basis of their requirement for hemin. Although the type strain of B. ruminicola subsp. brevis did not produce propionic acid, both of the present isolates classified as this subspecies produced substantial amounts. One strain of B. ruminicola subsp. brevis had an absolute requirement for volatile fatty acids. Either isobutyric or DL-2-methylbutyric acid would satisfy this requirement, whereas isovaleric acid was ineffective. It is of interest that xylan-fermenting bacteria isolated from 107 and 108 dilutions of rumen contents by use of a xylan medium are similar to the xylan fermenters isolated at the same dilutions with a nonselective medium. Fermentation of the fiber portion of forages, probably one of the more important functions of the rumen bacterial population, has primarily been studied in pure culture, with regard only to those bacteria which can' attack the cellulosic fraction. The ability of mixed cultures of rumen bacteria and several species isolated in pure culture to digest hemicellulose has been reviewed in an earlier publication (14). Bryant (3, 4) has listed a number of rumen bacterial species which are known to ferment xylan, a major portion of the hemicellulose fraction of forages. However, most of these bacteria were isolated with a nonselective medium. Butterworth, Bell, and Gar1 Approved for publication as Journal Article No. 103-65 by the Associate Director of the Ohio Agricultural Research and Development Center, Wooster, Ohio. vock (11), using wheat flour pentosan as a substrate, isolated a xylan-fermenting bacterium from the bovine rumen and tentatively assigned it to the genus Butyrivibrio. A sheep rumen bacterium was isolated by Walker (22) with the use of a medium containing wheaten hay hemicellulose as the only added carbohydrate. This organism was tentatively placed in the genus Bacteroides on the basis of fermentation products and biochemical characteristics. Hobson and Purdom (16) isolated two types of xylan-fermenting sheep rumen bacteria in the wheat flour pentosan medium previously described by Butterworth et al. (11). One organism was identified as a species of Butyrivibrio, and the second organism, a gramvariable coccobacillus, was studied in some detail but not named. The present paper describes the isolation and characterization of a number of strains of bovine rumen bacteria isolated in a me1724 on S etem er 3, 2017 by gest http/jb.asm .rg/ D ow nladed fom XYLAN-FERMENTING RUMEN BACTERIA dium with purified xylan as the only added carbo-