Hydrogen Production from Methane by Methylomonas sp. DH-1 under Micro-aerobic Conditions

Fueled by the recognition of hydrogen as a promising renewable energy source for the future, there have been many attempts to find greener and more economical ways for its production from various sources. In this study, Methylomonas sp. DH-1, a type I methanotroph, was found to produce hydrogen using methane as a sole carbon source, under micro-aerobic conditions; this is analogous to the partial oxidation of methane in a thermochemical process based on metal catalysts. Flask cultures of Methylomonas sp. DH-1 were used to investigate the effects of different culture conditions on hydrogen production, including oxygen levels, methane/oxygen ratios, and initial cell densities. Methylomonas sp. DH-1 could produce hydrogen at an oxygen level below 4%, regardless of the methane content in the flask, implying that the critical factor for hydrogen production is the oxygen level, rather than the methane/oxygen ratio. Moreover, Methylomonas sp. DH-1 shows reversibility in hydrogen production and uptake, because the strain produces hydrogen under micro-aerobic conditions, uptakes it when the oxygen levels increase, and restores the hydrogen production capability when conditions become microaerobic again. Under initial conditions of 30% methane, 70% air, and an OD600nm of 6, hydrogen production was 26.87 μmol and its yields per methane and dry cell weight were 14.98 mmol-H2/mol-CH4 and 101.53 μmol-H2/g DCW, respectively, after 24 h of cultivation.