Optimization of inorganic carbon sources to improve the carbon fixation efficiency of the non-photosynthetic microbial community with different electron donors

As the non-photosynthetic microbial community (NPMC) isolated from seawaters utilized inorganic carbon sources for carbon fixation, the concentrations and ratios of Na₂CO₃, NaHCO₃, and CO₂ were optimized by response surface methodology design. With H₂ as the electron donor, the optimal carbon sources were 270 mg/L Na₂CO₃, 580 mg/L NaHCO₃, and 120 mg/L CO₂. The carbon fixation efficiency in response to total organic carbon (TOC) was up to 30.59 mg/L with optimal carbon sources, which was about 50% higher than that obtained with CO₂ as the sole carbon source. The mixture of inorganic carbon sources developed a buffer system to prevent acidification or alkalization of the medium caused by CO₂ or Na₂CO₃, respectively. Furthermore, CO₂ and HCO₃−, the starting points of carbon fixation in the pathways of Calvin–Benson–Bassham and 3-hydroxypropionate cycles, were provided by the carbon source structure to facilitate carbon fixation by NPMC. However, in the presence of mixed electron donors composed of 1.25% Na₂S, 0.50% Na₂S₂O₃, and 0.457% NaNO₂, the carbon source structure did not exhibit significant improvement in the carbon fixation efficiency, when compared with that achieved with CO₂ as the sole carbon source. The positive effect of mixed electron donors on inorganic carbon fixation was much higher than that of the carbon source structure. Nevertheless, the carbon source structure could be used as an alternative to CO₂ when using NPMC to fix carbon in industrial processes. Copyright © 2014 Taylor & Francis.