An iron corrosion-assisted H-supplying system: a culture method for methanogens and acetogens under low H pressures.

H is an important fermentation intermediate in anaerobic environments. Although H occurs at very low partial pressures in the environments, the culture and isolation of H-utilizing microorganisms is usually carried out under very high H pressures, which might have hampered the discovery and understanding of microorganisms adapting to low H environments. Here we constructed a culture system designated the "iron corrosion-assisted H-supplying (iCH) system" by connecting the gas phases of two vials (one for the iron corrosion reaction and the other for culturing microorganisms) to achieve cultures of microorganisms under low H pressures. We conducted enrichment cultures for methanogens and acetogens using rice paddy field soil as the microbial source. In the enrichment culture of methanogens under canonical high H pressures, only Methanobacterium spp. were enriched. By contrast, Methanocella spp. and Methanoculleus spp., methanogens adapting to low H pressures, were specifically enriched in the iCH cultures. We also observed selective enrichment of acetogen species by the iCH system (Acetobacterium spp. and Sporomusa spp.), whereas Clostridium spp. predominated in the high H cultures. These results demonstrate that the iCH system facilitates culture of anaerobic microorganisms under low H pressures, which will enable the selective culture of microorganisms adapting to low H environments.