Apparent Incorporation of Ammonia and Amino Acid Carbon During Growth of Selected Species of Ruminal Bacteria

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Abstract
Apparent NH3 and amino acid-C14 incorporation into cells during growth of 22 strains representing 14 species known to be among the predominant rumen bacteria in cattle on many dietary regimes was determined in an anaerobic medium containing both NH3 and protein hydrolysate-C14 as sources of N. Representatives of six ruminal species in-corporated large amounts of C14[long dash]5.1 to 8.8% of total culture C per micromole of trichloroacetic acid-precipitable nitrogen produced (TCA-N)[long dash]and either incorporated little NH3 or produced it, and none require exogenous NH3. Strains of six species incorporated large amounts of NH3 (0.8-2.0 mole per mole TCA-N), small amounts of C14, (0.5-2.3%) and require NH3. Strains of two species incorporated small amounts of C14, variable amounts of NH3, and do not require exogenous NH3. One of the latter species did not incorporate a large amount of C14 even when forced to utilize mainly protein hydrolysate nitrogen other than NH3. Three strains requiring NH3 fixed intermediate amounts of both C14 and NH3. The results suggest that a significant proportion of the rumen bacterial population prefers to synthesize much of its cellular constituents from NH3-N and carbon sources otherthan amino acids.