Feasibility of a two-step culture method to improve the CO2-fixing efficiency of nonphotosynthetic microbial community and simultaneously decrease the spontaneous oxidative precipitates from mixed electron donors.

When compared with H2, mixed electron donors (MED), comprising S(2-), S2O3 (2-), and NO2 (-), could generally improve the CO2-fixing efficiency of nonphotosynthetic microbial communities (NPMCs). However, a large amount of abiotic precipitates combined with bacteria produced during culture may be unfavorable for the recycling and reuse of bacteria. The main component of the abiotic precipitates is S(0), which influences the enrichment and reuse of bacteria but is not conducive for CO2 fixation in the subsequent step. In this study, a two-step culture method (TSCM), employing H2 and MED, respectively, was verified to be feasible for improving the CO2-fixing efficiency of NPMCs in the second step. In the TSCM, the net-fixed CO2 increased to 854 mg/L and abiotic precipitates were not produced in the medium. Sequence analysis of 16 s rDNA from NPMC indicated the presence of microbial symbioses in the NPMC, supporting the possible applications of TSCM.