Carbon Monoxide Exposure Stimulates Growth and Activity of Primary Producers in Diverse Soil Ecosystems

Carbon monoxide (CO) is both a potent poison for many aerobic organisms and a desirable energy source for diverse microorganisms. Atmospheric emissions of this gas have increased since industrialization, and their levels are highly elevated in many urban and natural environments; however, it is unresolved whether elevated levels of CO at environmentally relevant concentrations are primarily stimulatory or inhibitory to soil microbial communities. Here, we showed that CO exposure minimally affects microbial abundance, richness, and composition in diverse ecosystem soils, suggesting that most microbes are tolerant of this gas. Genome-resolved metagenomic profiling showed that these soils harbored diverse bacteria capable of using CO as an electron donor for aerobic respiration and carbon fixation. CO stimulated the growth of several of these putative CO-oxidizing bacteria in a dose-dependent manner, especially widespread proteobacterial and actinobacterial lineages. Additionally, we found a strong relationship between CO oxidation and carbon fixation and observed an enrichment of several carboxydotrophic MAGs capable of carbon fixation in most soil types. These findings highlight that environmentally relevant CO levels do not inhibit soil microbes but instead foster the growth of distinct carboxydotrophic bacteria, suggesting a robust soil CO sink that could help mitigate anthropogenic CO emissions and identify new players contributing to carbon cycling in terrestrial ecosystems.