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

Souichiro Kato,Hanako Mochimaru,Hideyuki Tamaki,Kensuke Igarashi,Daisuke Mayumi,Motoko Takashino

doi:10.1038/s41598-020-76267-z

Abstract

H2 is an important fermentation intermediate in anaerobic environments. Although H2 occurs at very low partial pressures in the environments, the culture and isolation of H2-utilizing microorganisms is usually carried out under very high H2 pressures, which might have hampered the discovery and understanding of microorganisms adapting to low H2 environments. Here we constructed a culture system designated the “iron corrosion-assisted H2-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 H2 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 H2 pressures, only Methanobacterium spp. were enriched. By contrast, Methanocella spp. and Methanoculleus spp., methanogens adapting to low H2 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 H2 cultures. These results demonstrate that the iCH system facilitates culture of anaerobic microorganisms under low H2 pressures, which will enable the selective culture of microorganisms adapting to low H2 environments.

Highlights

Molecular hydrogen (H2) is an important intermediary metabolite and an energy carrier in anaerobic environments[1,2,3]
Because the growth of microorganisms is considered to be very slow under low H2 pressures, the culture system requires a continuous supply of H2 over a long period of time
We evaluated the capability of the iron corrosion-assisted H2-supplying (iCH) system to culture microorganisms under low H 2 pressures using a hydrogenotrophic methanogen Methanobacterium formicicum, which is known to be able to grow under both high and low H2 partial pressures[23], as a model strain

Summary

Introduction

Molecular hydrogen (H2) is an important intermediary metabolite and an energy carrier in anaerobic environments[1,2,3]. Culture and isolation of H2-utilizing microorganisms have commonly been performed under high H2 partial pressures (100 kPa or more). Under such laboratory conditions, it is difficult to draw conclusions about the ecophysiology of H2-utilizing microorganisms in their natural environment, nor can microorganisms that have adapted to conditions with low H 2 be isolated. The authors demonstrated that hydrogenotrophic methanogens can be cultured using H2 derived from metallic iron as sole energy source This method has not been applied to culture microorganisms adapted to low H2 environments. We report that a culture system based on iron corrosion reactions has been successfully used for the selective enrichment of hydrogenotrophic methanogens and acetogens, which have the potential to adapt to environments with very low H2 content

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