Fixation of CO2, electron donor and redox microenvironment regulate succinic acid production in Citrobacter amalonaticus.

Biological sequestration of CO2 for generating value added products is an emerging strategy. Succinic acid (SA) is an important C4 building block chemical, and its biological production via CO2 sequestration, holds many practical applications. This study presents an in-depth insight on SA production using isolated strain belonging to genus Citrobacter, more closely related to Citrobacter amalonaticus by considering critical process parameters such as different carbon sources at various initial concentrations, buffering agent (NaHCO3) concentrations and different pH conditions. The effect of H2 gas as an electron donor and availability of CO2 during SA production was also evaluated. The results from this work demonstrated that the isolated strain depicted the ability to utilize diverse carbon sources and highest SA production was achieved with sucrose as a substrate, indicating that reduced carbon substrates help in maximizing the redox potential. Incorporation of CO2 and H2 not only enhanced the production of SA but also affected the total acids profile favoring the production of SA over lactic, formic and acetic acids. Additional supply of CO2 and H2 led to maximum SA production of 12.07 gL-1, productivity of 0.36 gL-1 h-1 and SA yield of 48.5%. In control operation when no gases were supplied and in other test conditions where either of the gases were supplied, lactic acid was the major end product followed by acetic acid. The positive effect of CO2 for SA production provides scope for sustainable integration of SA and the CO2-generating biofuel industries or industrial side streams.