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Production of Isovaleric Acid from Leucine by Bacteroides ruminicola

Animal Husbandry Research Division, Beltsville, Maryland and Department of Microbiology, University of Maryland, College Park

ABSTRACT

Certain branch-chained volatile fatty acids such as isovaleric acid are essential for the growth of several species of cellulolytic ruminal bacteria (1, 3). Such acids are produced from mixtures of amino acids incubated with the mixed ruminal population (5). It has been suggested that the precursor of isovaleric acid is leucine (4, 5). The species of ruminal microorganisms which convert amino acids to branch-chained volatile fatty acids have not been identified.

Recent work indicates that Bacteroides ruminicola plays an important role in production of ammonia from amino acids in the rumen (2). Further studies indicated that ammonia production from single or pairs of amino acids by washed suspensions of B. ruminicola subsp. brevis (Strain 118B) was erratic and the only amino acids that on occasion gave definitely detectable ammonia production were DL-serine, L-aspartic acid, and L-cysteine. However, casein hydrolysates gave consistently good ammonia production. It was believed that perhaps with more sensitive methods the breakdown of other amino acids could be detected.

² Present address: Clinical Pathology, National Institutes of Health, Bethesda, Maryland.