[Effects of pH on methanogenesis and methanogenic community in the cultures amended with acetate].

Objective: To evaluate the effects of pH on methane production from acetate and the methanogenic community structures.

Methods: Solutions of phosphate (PB), 2-hydroxyethyl (HEPES), NaHCO3/CO2 or piperazine-1,4-bisethanesulfonic acid (PIPES) were added into the methanogenic cultures, separately. The substrate consumption was determined by monitoring cumulative methane production, the methanogenic community structuresin the stationary-phase cultures were analyzed using terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA gene fragments.

Results: The period of lag phase of methane production in the PB addition culture (ca. 40 d) was much longer than that in other pH buffer cultures (20 - 24 d, P < 0.05). Approximate 88.3% of acetate was converted into methane in the NaHCO3/CO2 addition culture, while the value decreased to 77% - 81% in other pH buffer cultures (P < 0.05). The maximum specific methane production rate was similar between different pH buffer cultures (P > 0.05). The relative abundance of members of unclassified bacteria, Spirochaetaceae and uncultured WWE1 increased to (15.5 ± 9.4)%, (7.3 ± 4.6)% and (17.6 ± 6.3)%, respectively, in the NaHCO3/CO2 addition culture, while synergistaceae decreased to (8.9 ± 8.1)%. In archaeal domain, the acetotrophic methanogen related with Methanosaeta harundinacea became predominant (97 ± 2%) in the PB buffer culture, on the contrary, the concurrence of M. harundinacea, M. concilii and hydrogenotrophic methanogen related with Methanobacteriales were detected in the cultures amended with HEPES, PIPES and NaHCO3/CO2.

Conclusion: PB retarded the methane production in the acetatemethanogenic culture, NaHCO3/CO2 addition improve methane production from acetate, the pH buffers had not obvious effects on the maximum specific methane production rate of the cultures, the microbial community structures obviously changed along with PB and NaHCO3/CO2 addition. The research would help us to design suitable condition for the growth of methanogenic culture.