H ₂-saturation of high affinity H ₂-oxidizing bacteria alters the ecological niche of soil microorganisms unevenly among taxonomic groups

Abstract

Soil microbial communities are continuously exposed to H ₂ diffusing into the soil from the atmosphere. N ₂-fixing nodules represent a peculiar microniche in soil where H ₂ can reach concentrations up to 20,000 fold higher than in the global atmosphere (0.530 ppmv). In this study, we investigated the impact of H ₂ exposure on soil bacterial community structure using dynamic microcosm chambers simulating soil H ₂ exposure from the atmosphere and N ₂-fixing nodules. Biphasic kinetic parameters governing H ₂ oxidation activity in soil changed drastically upon elevated H ₂ exposure, corresponding to a slight but significant decay of high affinity H ₂-oxidizing bacteria population, accompanied by an enrichment or activation of microorganisms displaying low-affinity for H ₂. In contrast to previous studies that unveiled limited response by a few species, the relative abundance of 958 bacterial ribotypes distributed among various taxonomic groups, rather than a few distinct taxa, was influenced by H ₂ exposure. Furthermore, correlation networks showed important alterations of ribotype covariation in response to H ₂ exposure, suggesting that H ₂ affects microbe-microbe interactions in soil. Taken together, our results demonstrate that H ₂-rich environments exert a direct influence on soil H ₂-oxidizing bacteria in addition to indirect effects on other members of the bacterial communities.