Distinct hydrogenotrophic bacteria are stimulated by elevated H2levels in upland and wetland soils

Abstract

AbstractBackgroundMolecular hydrogen (H2) is a major energy source supporting bacterial growth and persistence in soil ecosystems. While recent studies have uncovered mediators of atmospheric H2consumption, far less is understood about how soil microbial communities respond to elevated H2levels produced through natural or anthropogenic processes. Here we performed microcosm experiments to resolve how microbial community composition, capabilities, and activities change in upland (meadow, fluvo-aquic soil) and wetland (rice paddy, anthrosols soil) soils following H2supplementation (at mixing doses from 0.5 to 50,000 ppmv).ResultsGenome-resolved metagenomic profiling revealed that these soils harbored diverse bacteria capable of using H2as an electron donor for aerobic respiration (46 of the 196 MAGs from eight phyla) and carbon fixation (15 MAGs from three phyla). H2stimulated the growth of several of these putative hydrogenotrophs in a dose-dependent manner, though the lineages stimulated differed between the soils; whereas actinobacterial lineages encoding group 2a [NiFe]-hydrogenases grew most in the upland soils (i.e. Mycobacteriaceae, Pseudonocardiaceae), proteobacterial lineages harboring group 1d [NiFe]-hydrogenases were most enriched in wetland soils (i.e. Burkholderiaceae). Hydrogen supplementation also influenced the abundance of various other genes associated with biogeochemical cycling and bioremediation pathways to varying extents between soils. Reflecting this, we observed an enrichment of a hydrogenotrophicNoviherbaspirillumMAG capable of biphenyl hydroxylation in the wetland soils and verified that H2supplementation enhanced polychlorinated biphenyl (PCB) degradation in these soils, but not the upland soils.ConclusionsOur findings suggest that soils harbour different hydrogenotrophic bacteria that rapidly grow following H2exposure. In turn, this adds to growing evidence of a large and robust soil H2sink capable of counteracting growing anthropogenic emissions.