Enhancement of methanol production from synthetic gas mixture by Methylosinus sporium through covalent immobilization

Both methane (CH4) and carbon dioxide (CO2) are major greenhouse gases (GHGs); hence, effective processes are required for their conversion into useful products. CH4 is used by a few groups of methanotrophs to produce methanol. However, to achieve economical and sustainable CH4 reduction strategies, additional strains are needed that can exploit natural CH4 feed stocks. In this study, we evaluated methanol production by Methylosinus sporium from CH4 and synthetic gas. The optimum pH, temperature, incubation period, substrate, reaction volume to headspace ratio, and phosphate buffer concentration were determined to be 6.8, 30 °C, 24 h, 50% CH4, 1:5, and 100 mM (with 20 mM MgCl2 [a methanol dehydrogenase inhibitor]), respectively. Optimization of the production conditions and process parameters significantly improved methanol production from 0.86 mM to 5.80 mM. Covalent immobilization of M. sporium on Chitosan significantly improved the stability and reusability for up to 6 cycles of reuse under batch culture conditions. The immobilized cells utilized a synthetic gas mixture containing CH4, CO2, and hydrogen (at a ratio of 6:3:1) more efficiently than free cells, with a maximum methanol production of 6.12 mM. This is the first report of high methanol production by M. sporium covalently immobilized on a solid support from a synthetic gas mixture. Utilization of cost-effective feedstocks derived from natural resources will be an economical and environmentally friendly way to reduce the harmful effects of GHGs.