Association of methanogenic bacteria with rumen protozoa

Abstract

Methanogenic bacteria superficially associated with rumen entodiniomorphid protozoa were observed by fluorescence microscopy. A protozoal suspension separated from strained rumen fluid (SRF) by gravity sedimentation exhibited a rate of CH4 production 6 times greater (per ml) than SRF. The number of protozoa (per ml) in the protozoal suspension was 3 times greater than that of SRF; however, the urease activity of this fraction was half that of SRF. The methanogenic activity of SRF and the discrete fractions obtained by sedimentation of protozoa correlated with the numbers of protozoa per ml in each fraction. Gravity-sedimented protozoa, washed 4 times with cell-free rumen fluid, retained 67-71% of the recoverable methanogenic activity. Thus, many methanogens adhere to protozoa and evidently the protozoa support methanogenic activity of the attached methanogens. When protozoa-free sheep were inoculated with rumen contents containing a complex population of protozoa, methanogenic activity of the microflora in SRF samples was not significantly enhanced.