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

Abstract The universality of improved CO 2 fixing upon the addition of mixed electron donors (MEDs) composed of Na 2 S, NO 2 − , and S 2 O 3 2 − to non-photosynthetic microbial communities (NPMCs) obtained from 12 locations in four oceans of the world was validated. The CO 2 fixing efficiencies of NPMCs were universally enhanced by MED compared with those obtained using H 2 alone as electron donor, with average increase of about 276%. An increase in microbial inoculation concentration could increase the net amount of CO 2 fixing to 853.34 mg/L in the presence of MED. NO 2 − and S 2 O 3 2 − 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 CO 2 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 CO 2 fixing system. The interaction between autotrophic and heterotrophic bacteria may be a crucial factor supporting ladder utilization and recycling of energy/carbon source.