Affiliation:
1. Physiopathological Investigations Section, National Animal Disease Laboratory, Ames, Iowa 50010
Abstract
Microorganisms in ruminal ingesta and pure cultures of anaerobic ruminal bacteria of different physiological and morphological groups incorporated
14
C from labeled 2-methylbutyrate during growth. The radioactivity was incorporated mainly into lipid and protein. Isoleucine was the only labeled amino acid found in acid hydrolysates of protein from either pure or mixed cultures. Radioactivity in isoleucine synthesized from 2-methylbutyrate-
1
-
14
C
was entirely in carbon-2. Thus, the carboxylation of 2-methylbutyrate is a pathway for synthesis of isoleucine different from that operative in many aerobic and facultative microorganisms. The specific activity of isoleucine from 2-methylbutyrate by
Bacteroides rumminicola
23 increased with higher concentrations of 2-methylbutyrate (2.6 to 44 × 10
−5
m
) in the growth medium. At the highest concentration, the specific activity of isoleucine synthesized was 40% of the specific activity of the 2-methylbutyrate in the growth medium. The use of enzymatic casein hydrolysate, oxytocin, or vasopressin rather than ammonia as nitrogen source for growth of strain 23 depressed the incorporation of 2-methylbutyrate into isoleucine. Synthesis of isoleucine from 2-methylbutyrate appears to be an important reaction in the rumen.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology