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

Abstract

The incorporation of urea N 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 TCA. The TCA precipitated mainly cell wall material, while TA precipitated the soluble cellular and extracellular proteins as well. Total N 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 TA gave a better estimate of bacterial growth. Synthesis of this fraction followed more closely the build-up of total cell N and was more highly correlated with bacterial activity than the nitrogenous fraction precipitated by TCA. The growth limiting effect of low valeric-acid fermentations was reflected in the amounts of cytoplasmic proteins synthesized, but the build-up of cell wall material was not restricted.