Matching Different Inorganic Compounds as Mixture of Electron Donors to Improve CO2 Fixation by Nonphotosynthetic Microbial Community without Hydrogen

The dominant bacteria in nonphotosynthetic microbial community (NPMC) isolated from the ocean were identified by PCR-DGGE. The results revealed that the dominant microorganisms in cultures of NPMC differed when Na2S, Na2S2O3, and NaNO2 were used as the electron donor to reduce CO2. These findings implied that different microorganisms in the NPMC respond to different inorganic compound as suitable electron donor, indicating that matching of Na2S, Na2S2O3, and NaNO2 may provide mixed electron donors that increase the ability of NPMC to fix CO2. Accordingly, the central composite response surface method (RSM) was used to predict the optimal concentration and match of Na2S, Na2S2O3, and NaNO2 as mixed electron donors to improve CO2 fixation efficiency under aerobic and anaerobic conditions without hydrogen. The results indicated that 0.46% NaNO2, 0.50% Na2S2O3, and 1.25% Na2S were the optimal match under aerobic conditions, while 1.04% NaNO2, 1.07% Na2S2O3, and 0.98% Na2S were the optimal match under anaerobic conditions. Under these conditions, the fixed CO2 by NPMC was determined to be 387.51 and 512.57 mg/L, respectively, which obviously exceeded those values obtained prior to optimization (5.94 and 7.14 mg/L, respectively), as well as that obtained when hydrogen was used as the electron donor (91.60 mg/L).