ENUMERATION OF H-2-UTILIZING METHANOGENIC ARCHAEA, ACETOGENIC AND SULFATE-REDUCING BACTERIA FROM HUMAN FECES

Fecal specimens from 19 healthy humans were used to enumerate H-2-utilizing microbial populations of methanogenic archaea (MA), acetogenic bacteria (AB) and sulfate-reducing bacteria (SRB). Eight subjects were methane (CH4) excretors (CH4+) and 11 non CH4-excretors (CH4-), based on breath methane concentrations. The mean +/- S.E. of the logarithm of MA per gram wet weight feces were 8.8 +/- 0.21 and 2.6 +/- 0.39 for CH4+ and CH4-, respectively (P < 0.001). SRS counts were 7.1 +/- 0.43 and 7.3 +/- 0.39, respectively (NS), while counts of AB were 4.6 +/- 0.75 and 6.6 +/- 0.38, respectively (P < 0.02). Counts of AB were negatively correlated with counts of MA (r = -0.53; P < 0.05). These results confirm the potential importance of AB in the human colon, especially for CH4- subjects, and suggest that a much greater competitive interrelation occurs in the human colon between MA and AB than between the former and SRB. We further report on the isolation of representatives of the dominant H-2/CO2 acetogenic population. Three strains from two CH4-subjects were characterized from 10(-5)-10(-7) dilutions. They all consumed H-2/CO2 and several carbohydrates to produce acetate as the sole metabolite. Phenotypically related to the species Peptostreptococcus productus, the strains used H-2/CO2 via the acetyl-CoA pathway.