Biotechnology and Bioprocess Engineering 2020; 25(1): 71-77  
Hydrogen Production from Methane by Methylomonas sp. DH-1 under Micro-aerobic Conditions
Seo Young Jo1, Mi Na Rhie1, Soo Min Jung2, Yu Jung Sohn1, Young Joo Yeon3, Min-Sik Kim4, Chulhwan Park5, Jinwon Lee2, Si Jae Park1,*, and Jeong-Geol Na2,*
1Division of Chemical Engineering and Materials Science, Ewha Womans University, Seoul 03760, Korea
2Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 04107, Korea
3Department of Biochemical Engineering, Gangneung-Wonju National University, Gangneung 25457, Korea
4Korea Institute of Energy Research, Gwangju 61003, Korea
5Department of Chemical Engineering, Kwangwoon University, Seoul 01897, Korea
Correspondence to: Si Jae Park*
Division of Chemical Engineering and Materials Science, Ewha Womans University, Seoul 03760, Korea
Tel: +82-2-3277-4756; Fax: +82-2-3277-3275
E-mail: parksj93@ewha.ac.kr
Jeong-Geol Na*
Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 04107, Korea
Tel: +82-2-705-7955; Fax: +82-2-705-8799
E-mail: narosu@sogang.ac.kr
Received: July 3, 2019; Revised: September 7, 2019; Accepted: September 21, 2019; Published online: February 29, 2020.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
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 micro-aerobic 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.
Keywords: Methylomonas sp. DH-1, methanotroph, hydrogen, methane, micro-aerobic conditions


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