Biosynthesis of Methanol from Carbon Dioxide by Methanotrophic Bacteria

Methanotrophs can oxidize methane to carbon dioxide through sequential reactions catalyzed by a series of enzymes including methane monooxygenase, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase. Reducing carbon dioxide to methanol is an opposite reaction of methanol oxidation, which requires a considerable amount of energy. So far there are no known organisms whose normal biological role is reduction of carbon dioxide to methanol. In this communication, we report that bioconversion of carbon dioxide to methanol was successfully achieved using resting cells of methanotrophic bacteria of Methylosinus trichosporium IMV 3011 as biocatalysts. Extracellular methanol accumulation has been found in the carbon dioxide incubations. The conversion of carbon dioxide to methanol is energy-intensive and requires reducing equivalent to push the reaction along against energy laws. For long-term maintenance of methanol synthesis, methane was selected as a substrate for regeneration of reducing equivalent. By alternate reaction and regeneration, the results show that resting cell of M. trichosporium IMV 3011 can be used for many times to catalyze the reduction of carbon dioxide, in which the origin of the reducing equivalent is methane. It is possible to theoretically deduce that the overall reaction for methanol synthesis can be completed by biocatalysis using greenhouse gases (carbon dioxide and methane) as raw materials without adding hydrogen. This new route should be environmentally friendly and a selective process operating at room temperature and normal pressure. Also, it is theoretically possible that the overall reaction can produce methanol without adding to the greenhouse effect.