Degradation of the nucleic acids in mixed rumen bacteria on incubation with different media.

1. Mixed rumen bacteria were grown in vitro in a medium containing [U-14C]adenine. Radioactivity was incorporated into the purine bases of the nucleic acids. 2. Labelled bacteria were incubated with a nitrogen-deficient cell-free medium (medium A), a protozoa-free supernatant suspension from a slow-speed centrifuging of a steer's rumen contents (medium B) and whole rumen contents of a steer (medium C). Mean (six experiments) proportional rates of release of radioactivity (/h) were significantly greater for medium A (0-140) than for media B or C (0-055 and 0-43 respectively). Some of the radioactivity accumulated in the cell-free media; some was lost, partially as carbon dioxide. 3. Calculation from this and other information indicated that about 30% of bacterial nucleic acids may turn over in the rumen even in the absence of protozoa.