Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO₂Concentration

Increasing CO₂emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO₂have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO₂concentrations, ferric oxide loading, and dolomite (CaMg(CO₃)₂) availability. The results showed that abiotic and biotic processes interactively mediate CO₂acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO₂stress on microbial activity, possibly via pH control that transforms the inhibitory CO₂to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H⁺) consumption during iron reduction and H⁺generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO₂to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO₃) under elevated CO₂, supporting its incorporation into solids. The results of these CO₂-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO₂acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO₂sequestration, and modeling of carbon flux).