Production of soluble methane monooxygenase during growth of Methylosinus trichosporium on methanol

Soluble methane monooxygenase (sMMO) can degrade many chlorinated and aromatic pollutants. It is produced by certain methanotrophs such as Methylosinus trichosporium when grown on methane under copper limitation but, due to its low aqueous solubility, methane cannot support dense biomass growth. Since it is water soluble, methanol may be a more attractive growth substrate, but it is widely believed that sMMO is not produced on methanol. In this study, when the growth-limiting substrate was switched from methane to methanol, in the presence of the particulate MMO inhibitor, allylthiourea, growth of M. trichosporium OB3b continued unabated and sMMO activity was completely retained. When allylthiourea was then removed, sMMO activity was maintained for an additional 24 generations, albeit at a slightly lower level due to the presence of 0.70 μM of Cu2+ in the feed medium. While a biomass density of only 2 g l−1 could be obtained on methane, 7.4 g l−1 was achieved by feeding methanol exponentially, and 29 g l−1 was obtained using a modified feeding strategy employing on-line carbon dioxide production measurement. It was concluded that methanol can be employed to produce large amounts of M. trichosporium biomass containing sMMO.