Metabolism of Urea Nitrogen by Mixed Cultures of Rumen Bacteria Grown on Cellulose

Abstract

The incorporation of urea nitrogen into protein and other nitrogenous compounds by mixed cultures of rumen bacteria grown on cellulose was studied in vitro, using trichloroacetic acid (TCA) and tungstic acid (TA) as protein precipitants. Tungstic acid precipitated more protein from the in vitro rumen fermentation than did trichloroacetic acid. TCA was shown to precipitate mainly cellular debris, whereas tungstic acid precipitated the soluble cellular and extracellular proteins as well. Total nitrogen in the in vitro fermentation mixture was accounted for in the following nitrogenous fractions: protein, peptide, amide, ammonia, and a trace of residual urea. Nitrogenous fractions precipitated by tungstic acid gave a better estimate of bacterial growth. Synthesis of this fraction followed more closely the build-up of total cell nitrogen and was more highly correlated with bacterial activity than the nitrogenous fraction precipitated by trichloroacetic acid. The growth-limiting effect of low valeric acid fermentations was reflected in the amounts of cytoplasmic proteins synthesized, but the build-up of cellular debris was not restricted. © 1964, American Dairy Science Association. All rights reserved.