Substituent effects on the oxidation of substituted biphenyl congeners by type II methanotroph strain CSC1

The oxidation potential of type II groundwater methanotroph, strain CSC1, expressing soluble methane monooxygenase, was measured in the presence of 10 ortho-substituted biphenyls with varying electronics, sterics, and hydrophobicity character for comparison with type II Methylosinus trichosporium OB3b. Strain CSC1 showed faster rates with all compounds tested, with the exception of 2-nitrobiphenyl, 2-hydroxybiphenyl, and 2-aminobiphenyl. Products of oxidation observed upon incubation of strain CSC1 with biphenyl and 2-hydroxybiphenyl were hydroxylated biphenyls that revealed less preference for the para position and different dihydroxylation positions, respectively, in comparison to those observed with M. trichosporium OB3b. Only the intramolecular hydrogen migration, or NIH-shift, product was observed in the case of 2-chlorobiphenyl, whereas M. trichosporium OB3b yielded a variety of chlorohydroxybiphenyls. Quantitative structure-biodegradation relationships constructed with the maximum observed oxygen uptake rates as a dependent variable and a variety of descriptors showed an influence of substituent electronic character on the oxidation activity of strain CSC1. However, compound hydrophobicity and not compound size, as was observed with M. trichosporium OB3b, was shown to influence rates to a greater extent. This suggests that transport of the compound through the cell membrane and to the sMMO active site is rate-determining for strain CSC1.