CO/HCO 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) is the predominant oxidation state in an aerobic environment. Hence, the reduction of Fe is of essential importance to meet the cellular demand of ferrous iron (Fe) but might become detrimental as excessive amounts of intracellular Fe tend to undergo the cytotoxic Fenton reaction in the presence of hydrogen peroxide. We demonstrate that the complex formation rate of Fe and phenolic compounds like protocatechuic acid was increased by 46% in the presence of HCO and thus accelerated the subsequent redox reaction, yielding reduced Fe Consequently, elevated CO/HCO levels increased the intracellular Fe availability, which resulted in at least 50% higher biomass-specific fluorescence of a DtxR-based reporter strain, and stimulated growth. Since the increased Fe availability was attributed to the interaction of HCO and chemical iron reduction, the abiotic effect postulated in this study is of general relevance in geochemical and biological environments. In an oxygenic environment, poorly soluble Fe must be reduced to meet the cellular Fe demand. This study demonstrates that elevated CO/HCO levels accelerate chemical Fe reduction through phenolic compounds, thus increasing intracellular Fe availability. A number of biological environments are characterized by the presence of phenolic compounds and elevated HCO levels and include soil habitats and the human body. Fe availability is of particular interest in the latter, as it controls the infectiousness of pathogens. Since the effect postulated here is abiotic, it generally affects the Fe distribution in nature.