Enhanced CO2 electroconversion of Rhodobacter sphaeroides by cobalt-phosphate complex assisted water oxidation

Enhancing microbial CO2 electrocatalysis for multicarbon reduction in a wet amine-based catholyte

Microbial CO2 electroreduction (mCO2ER) offers a promising approach for producing high-value multicarbon reductants from CO2 by combining CO2 fixing microorganisms with conducting materials (i. e., cathodes). However, the solubility and availability of CO2 in an aqueous electrolyte pose significant limitations in this system. This study demonstrates the efficient production of long-chain multicarbon reductants, specifically carotenoids (~C40), within a wet amine-based catholyte medium during mCO2ER. Optimizing the concentration of the biocompatible CO2 absorbent, monoethanolamine (MEA), led to enhanced CO2 fixation in the electroautotroph bacteria. Molecular biological analyses revealed that MEA in the catholyte medium redirected the carbon flux towards carotenoid biosynthesis during mCO2ER. The faradaic efficiency of mCO2ER with MEA for carotenoid production was 4.5-fold higher than that of the control condition. These results suggest the mass transport bottleneck in bioelectrochemical systems could be effectively addressed by MEA-assissted mCO2ER, enabling highly efficient production of valuable products from CO2.

Evaluation of Growth and Utilization Potential of Rhodobacter sphaeroides in Reused Medium

Rhodobacter sphaeroides is a metabolically versatile purple non-sulfur bacteria that can produce valuable substances. As the low-cost and high-efficiency production of valuable substances is attracting attention, the reuse of the medium is emerging as a promising strategy. Therefore, in this study, the growth of R. sphaeroides was evaluated by reusing the medium of Escherichia coli and Saccharomyces cerevisiae. As a result, in the reuse of the medium in which S. cerevisiae was cultured, sufficient growth of R. sphaeroides could be confirmed, and especially, the growth of R. sphaeroides was not inhibited under aerobic conditions. Therefore, it is considered that the strategy of reusing the medium of S. cerevisiae is sufficiently feasible. Of the organic compounds investigated, R. sphaeroides grew best in succinic acid, followed by malic acid, citric acid, acetic acid, and glucose. In addition, by comparing photopigment synthesis in the reused medium, we propose the hypothesis that succinic acid may play an important role in photopigment synthesis for the first time.