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.