Degradation of dimethyl nitrosamine by Methylosinus trichosporium OB3b

The degradation of dimethyl nitrosoamine (DMNA) by a methanotroph, Methylosinus trichosporium OB3b, was studied using 14C-labelled DMNA. The organism was capable of assimilating DMNA-carbon and converting it to CO2. The rates of CO2 production (VCO2) from DMNA and its cellular uptake (VP) were linearly correlated with DMNA concentrations of 0.03-10 mM, which corresponded to approximately 3% of added DMNA metabolized in 24 h. These rates were two to three orders of magnitude less than the rate of uptake of methane (VCH4. VCH4 was suppressed when the concentrations of DMNA exceeded 0.3 mM. In the presence of 0.1 mM DMNA, VP and VCO2 were essentially the same in the presence or absence of methane in the first 8 h of incubation, but declined sharply thereafter only when methane was absent. These observations suggest that the metabolism of DMNA was carried out by methane monooxygenase (MMO), and that NADH, a cofactor for MMO, may be provided by the oxidation of the stored compounds in the cells when methane is not available.