Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO 2 Concentration.

Increasing CO emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, , was cultured under 18 conditions that systematically varied in headspace CO concentrations, ferric oxide loading, and dolomite (CaMg(CO)) availability. The results showed that abiotic and biotic processes interactively mediate CO acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO stress on microbial activity, possibly via pH control that transforms the inhibitory CO to 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 CO to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO) under elevated CO, supporting its incorporation into solids. The results of these CO-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO sequestration, and modeling of carbon flux).