Soil microbial communities are continuously exposed to H2diffusing into the soil from the atmosphere. N2-fixing nodules represent a peculiar microniche in soil where H2can reach concentrations up to 20,000 fold higher than in the global atmosphere (0.530 ppmv). In this study, we investigated the impact of H2exposure on soil bacterial community structure using dynamic microcosm chambers simulating soil H2exposure from the atmosphere and N2-fixing nodules. Biphasic kinetic parameters governing H2oxidation activity in soil changed drastically upon elevated H2exposure, corresponding to a slight but significant decay of high affinity H2-oxidizing bacteria population, accompanied by an enrichment or activation of microorganisms displaying low-affinity for H2. 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 H2exposure. Furthermore, correlation networks showed important alterations of ribotype covariation in response to H2exposure, suggesting that H2affects microbe-microbe interactions in soil. Taken together, our results demonstrate that H2-rich environments exert a direct influence on soil H2-oxidizing bacteria in addition to indirect effects on other members of the bacterial communities.
Isolation of Streptomyces sp. PCB7, the first microorganism demonstrating high-affinity uptake of tropospheric H2
