METHANOGENS OUTCOMPETE SULFATE-REDUCING BACTERIA FOR H-2 IN THE HUMANCOLON

Methanogens and sulphate reducing bacteria compete for H-2 in the huma n colon, and, as a result, faeces usually contain high concentrations of just one of these two organisms. There is controversy over which of these organisms wins the competition for H-2, although theoretical da ta suggest that sulphate reducing bacteria should predominate. To eluc idate this question experiments were undertaken in which sulphate enri ched homogenates of human sulphate reducing faeces and methane produci ng faeces were incubated separately or mixed together. Co-incubation o f sulphate reducing faeces with methanogenic faeces resulted in a sixf old reduction in the activity of the sulphate reducing bacteria (measu red as sulphide production), whereas methane production was not inhibi ted by co-incubation with sulphate reducing bacteria. Methanogenic fae ces also consumed H-2 more rapidly and reduced the H-2 tension of the homogenate to a lower value than did sulphate reducing faecal samples. In these experiments, methanogens seem to outcompete sulphate reducin g bacteria for H-2.