Abstract
The competition for H2 substrate and the symbiotic relation between sulfate-reducing-bacteria (SRB) and methane-producing-bacteria (MPB) were investigated in this study for the acclimated-mixed-methanogens culture from CO2 and H2. The medium was cultured with antibiotics where growth of eubateria was inhibited but not methanogens, and without antibiotics where sulfate was used as a sulfur source. In the case of the medium without antibiotics, colony-forming-curves (CFC) of the SRB increased from 7.2×106/mL to 4.4×107/mL after 1 day of tube cultivation, while CFCs of MPB increased less rapidly. Entering growth phase after 2 days, CFCs of MPB rapidly increased from 1.6×109/mL to 2.2×1010/mL. In the case of the medium containing antibiotics, SRB was completely inhibited, thus sulfate reduction to sulfide was impossible. Comparison of CFCs of MPB and methane gas formation showed that numbers were less in the medium containing antibiotics, than in the medium without antibiotics. MPB were not capable of reducing sulfate to sulfide, thus CFCs and methane gas formation were reduced. These results suggested that SRB, which exists symbiotically with predominant methanogens, produced a sulfur source by reducing sulfate to sulfide. The reduction consequentially provided an environment for the development of strictly anaerobic organisms, thereby accelerating the growth of methanogens. The role that SRB played in symbiotic methanogenesis was evaluated and examined in this study.
