UREOLYTIC RUMEN BACTERIA: I. CHARACTERISTICS OF THE MICROFLORA FROM A UREA-FED SHEEP

Measurement of the urease activity of fractions of strained rumen fluid from a urea-fed sheep showed that intracellular bacterial urease was responsible for ureolysis by rumen contents. Subjection of the rumen microflora to differential centrifugation showed that 65% of its total urease activity was associated with a group of larger organisms which sedimented at 1200 × g. An average of 35% of the total viable bacteria in rumen fluid was found by a dilution count technique to manifest urease activity. Mixed cultures of rumen bacteria, in which the urease activity per unit concentration of cells was enriched fourfold over that in rumen-fluid, were obtained by serial transfer in a medium containing 80% rumen supernatant liquor (clarified rumen fluid) supplemented with glucose, phytone, and urea. A facultatively anaerobic bacterium with a low urease activity was isolated from rumen fluid, but attempts to isolate obligately anaerobic urease-producing species from enrichment cultures of rumen bacteria were unsuccessful.