THE ROLE OF CILIATE PROTOZOA IN THE LYSIS OF METHANOGENIC ARCHAEA IN RUMEN FLUID

Predation by ciliate protozoa can account for 90% of the eubacterial p rotein turnover in the rumen. However, little is known about the facto rs affecting the lysis of archaea in rumen fluid. Bacterial lysis was followed from the release of acid-soluble C-14 from C-14 leucine-label led bacteria. The rumen methanogen Methanobrevibacter MF1 was broken d own more rapidly than other non-ruminal archaea in rumen fluid withdra wn from sheep harbouring either a mixed protozoal population or monofa unated with Polyplastron multivesiculatum or Entodinium spp. The remov al of protozoa from the rumen fluid had little effect on the breakdown of Methanobrevibacter, while lysis of the non-methanogenic ruminal ba cterium Selenomonas ruminantium decreased by over 70%. Substantial lys is of Methanobrevibacter occurred in cell-free rumen fluid and this ef fect could be abolished by autoclaving. In view of the high number of bacteriophages in rumen fluid and susceptibility of ruminal bacteria t o phage-induced lysis it is tempting to suggest that phages have a rol e in the lysis of archaea in rumen fluid.