Characterization of toluene metabolism by methanotroph and its effect on methane oxidation.

Methanotrophs not only oxidize CH4, but also can oxidize a relatively broad range of other substrates, including trichloroethylene, alkanes, alkenes, and aromatic compounds. In this study, Methylosinus sporium was used as a model organism to characterize toluene metabolism by methanotrophs. Reverse transcription quantitative PCR analysis showed that toluene enhanced the mmoX expression of M. sporium. When the toluene concentration was below 2000 mg m-3, the kinetics of toluene metabolism by M. sporium conformed to the Michaelis-Menten equation (Vmax = 0.238 g gdry weight-1 h-1, K m  = 545.2 mg m-3). The use of a solid-phase extraction technique followed by a gas chromatography-mass spectrometry analysis and molecular docking calculation showed that toluene was likely to primarily bind the di-iron center structural region of soluble methane monooxygenase (sMMO) hydroxylase and then be oxidized to o-cresol. Although M. sporium oxidized toluene, it did not incorporate toluene into its biomass. The coexistence of toluene and CH4 could influence CH4 oxidation, the growth of methanotrophs, and the distribution of CH4-derived carbon, which were related to the ratio of the toluene concentration to biomass. These results would be helpful to understand the metabolism of CH4 and non-methane volatile organic compounds in the environment.