CO(2)/HCO(3)(−) Accelerates Iron Reduction through Phenolic Compounds

Iron is a vital mineral for almost all living organisms and has a pivotal role in central metabolism. Despite its great abundance on earth, the accessibility for microorganisms is often limited, because poorly soluble ferric iron (Fe(3+)) is the predominant oxidation state in an aerobic environment. Hence, the reduction of Fe(3+) is of essential importance to meet the cellular demand of ferrous iron (Fe(2+)) but might become detrimental as excessive amounts of intracellular Fe(2+) tend to undergo the cytotoxic Fenton reaction in the presence of hydrogen peroxide. We demonstrate that the complex formation rate of Fe(3+) and phenolic compounds like protocatechuic acid was increased by 46% in the presence of HCO(3)(−) and thus accelerated the subsequent redox reaction, yielding reduced Fe(2+). Consequently, elevated CO(2)/HCO(3)(−) levels increased the intracellular Fe(2+) availability, which resulted in at least 50% higher biomass-specific fluorescence of a DtxR-based Corynebacterium glutamicum reporter strain, and stimulated growth. Since the increased Fe(2+) availability was attributed to the interaction of HCO(3)(−) and chemical iron reduction, the abiotic effect postulated in this study is of general relevance in geochemical and biological environments.