TAXON-SPECIFIC ASSOCIATIONS BETWEEN PROTOZOAL AND METHANOGEN POPULATIONS IN THE RUMEN AND A MODEL RUMEN SYSTEM

Methanogen populations in the rumen and in model rumen systems (operat ed over a 240-h period) were studied using the small subunit (SSU) rRN A phylogenetic framework for group-specific enumerations. Representati ves of the family Methanobacteriaceae were the most abundant methanoge n population in the rumen, accounting for 89.3% (+/-1.02%) of total ar chaea in the rumen fluid and 99.2% (+/- 1.8%) in a protozoal fraction of rumen fluid. Their percentage of archaea in the model rumen systems declined from 84% (+/- 8.5%) to 54% (+/- 7.8%) after 48 h of operatio n, correlated with loss of protozoa from these systems. The Methanomic robiales, encompassed by the families Methanomicrobiaceae, Methanocorp usculaceae, and Methanospirillaceae were the second most abundant popu lation and accounted for 12.1% (+/- 2.15%) of total SSU rRNA in rumen fluid. Additionally this group was shown to be essentially free living , since only a negligible hybridization signal was detected with the r uminal protozoal fraction. This group constituted a more significant p roportion of total archaea in whole rumen fluid, 12.1% (+/- 2.1%) and model rumen fluid containing no protozoa (26.3 +/- 7.7%). In contrast, the Methanosarcinales, generally considered the second most abundant population of rumen methanogens, accounted for only 2.8% (+/- 0.3%) of total archaeal SSU rRNA in rumen fluid. (C) 1998 published by Elsevie r Science B.V.