Universally improving effect of mixed electron donors on the CO2 fixing efficiency of non-photosynthetic microbial communities from marine environments

The universality of improved CO2 fixing upon the addition of mixed electron donors (MEDs) composed of Na2S, NO2−, and S2O32 − to non-photosynthetic microbial communities (NPMCs) obtained from 12 locations in four oceans of the world was validated. The CO2 fixing efficiencies of NPMCs were universally enhanced by MED compared with those obtained using H2 alone as electron donor, with average increase of about 276%. An increase in microbial inoculation concentration could increase the net amount of CO2 fixing to 853.34 mg/L in the presence of MED. NO2− and S2O32 − may play the roles of both electron acceptor and electron donor under aerobic conditions, which may improve the energy utilization efficiency of NPMC and enhance the CO2 fixation efficiency. The sequence determination of 16S ribosomal deoxyribonucleic acid (rDNA) from 150 bacteria of NPMC showed that more than 50% of the bacteria were symbiotic and there were many heterotrophic bacteria such as Vibrio natriegens. These results indicate that NPMC acts as a symbiotic CO2 fixing system. The interaction between autotrophic and heterotrophic bacteria may be a crucial factor supporting ladder utilization and recycling of energy/carbon source.