Performance and mechanism of carbon dioxide fixation by a newly isolated chemoautotrophic strain Paracoccus denitrificans PJ-1.

CO2 is regarded as a major contributor to the global warming. CO2 utilization is promising to reduce the CO2 emissions. Currently, the biofixation of CO2 using chemoautotrophs has markedly gain interest in CO2 utilization. In this study, a newly isolated chemoautotroph, Paracoccus denitrificans PJ-1, was used for the biofixation of CO2 under anaerobic condition. Experimental results revealed that Paracoccus denitrificans PJ-1 achieved a high carbon fixation rate (13.25 mg·L-1·h-1) which was ∼10 times faster than the previous reported chemotrophic bacteria using thiosulfate as electron donor. The best CO2 fixation activity of Paracoccus denitrificans PJ-1 was achieved at the pH value of 9.0 and CO2 concentration of 20 vol%. Meanwhile, a high CO2 fixation yield of 106.03 mg·L-1 was reached. The presence of oxygen was adverse to the biofixation, indicating that strain PJ-1 was more suitable for CO2 fixation in anaerobic environments. Carbon mass balance analysis revealed that the carbon from CO2 was mainly fixed into the extracellular organic carbon rather than the biomass. GC-MS analysis and cbbL gene test revealed that Paracoccus denitrificans PJ-1 fixed CO2 through the Calvin-Benson-Bassham cycle and mainly converted CO2 to oxalic acid and succinic acid. Overall, the excellent CO2 fixation capacity of Paracoccus denitrificans PJ-1 suggests that it had potential for CO2 utilization.