An iron corrosion-assisted H2-supplying system: a culture method for methanogens and acetogens under low H2 pressures

H 2 is an important fermentation intermediate in anaerobic environments. Although H 2 occurs at very low partial pressures in the environments, the culture and isolation of H 2 -utilizing microorganisms is usually carried out under very high H 2 pressures, which might have hampered the discovery and understanding of microorganisms adapting to low H 2 environments. Here we constructed a culture system designated the “iron corrosion-assisted H 2 -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 2 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 2 pressures, only Methanobacterium spp. were enriched. By contrast, Methanocella spp. and Methanoculleus spp., methanogens adapting to low H 2 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 2 cultures. These results demonstrate that the iCH system facilitates culture of anaerobic microorganisms under low H 2 pressures, which will enable the selective culture of microorganisms adapting to low H 2 environments.