I am posting this here since it is off topic for the other thread . It is about methanogenic and sulfate reducing bacteria Title: Interrelations between populations of methanogenic archaea and sulfate-reducing bacteria in the human colon. Author: Pochart P , DorÃ© J , LÃ©mann F , Goderel I , Rambaud JC Source FEMS Microbiol Lett, 77(1-3): 225-8 1992 Abstract: In humans, CH4 is produced in the colon by methanogenic archaea and is detected in breath samples from approximately 50% of healthy adults, identified as CH4-excretors. Methanogenesis and sulfate reduction have been described as two mutually exclusive processes, potentially regulated by sulfate availability. To determine whether microbial population balances reflected these apparently co-regulated activities, we compared sulfate-reducing bacteria, methanogenic archaea, sulfate and sulfide concentrations in faeces of 10 CH4-excretors (CH4+) and 9 non-CH4-excretors (CH4-). The mean +/- SE of the logarithm of methanogenic archaea per gram wet weight were 9.0 +/- 0.2 and 4.0 +/- 0.7 for CH4+ and CH4-, respectively (P < 0.001). Sulfate-reducing bacterial counts were 6.5 +/- 0.1 and 7.3 +/- 0.2, respectively (P < 0.001). Fecal sulfate and sulfide concentrations did not differ between groups. These results suggest that a competitive interrelation between methanogenic archaea and sulfate-reducing bacteria occurs in the human colon. However, it does not lead to a complete exclusion of the two populations The paper seems to differentiate between the process and the population. It seems to say the populations are not mutually exclusiveAnd am repeating a question from the last thread bcos maybe you missed it - Do you know the names of malodorous gases made by non sulfate reducing bacteria?