Enumeration of H2-utilizing methanogenic archaea, acetogenic and sulfate-reducing bacteria from human feces
Fecal specimens from 19 healthy humans were used to enumerate H2-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). SRB 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 H2CO2 acetogenic population. Three strains from two CH4 — subjects were characterized from 10−5-10−7 dilutions. They all consumed H2CO2 and several carbohydrates to produce acetate as the sole metabolite. Phenotypically related to the species Peptostreptococcus productus, the strains used H2CO2 via the acetyl-CoA pathway.