Transformation of ortho-substituted biphenyls by Methylosinus trichosporium OB3b:: substituent effects on oxidation kinetics and product formation

The ability of Methylosinus trichosporium OB3b, expressing soluble methane monooxygenase, to oxidize a range of ol-tho-substituted biphenyls was examined to better understand how substituents affect both the rate and products of oxidation in comparison to biphenyl. Inhibition of oxidation was observed over the tested substrate range for both biphenyl and ortho-halogenated biphenyls (2-chloro-, 2-bromo-, and 2-iodobiphenyl), No inhibition was observed during the oxidation of 2-hydroxybiphenyl and 2-methylbiphenyl. Analysis of the products of oxidation showed that, depending on the substituent, ring hydroxylation, substituent oxidation, and elimination pathways could occur. The type and abundance of products formed along with the relatively high kinetic isotope effect observed for deuterated vs. nondeuterated biphenyl (k(h)/k(d) = 3.4 +/- 0.02) are consistent with mechanisms that include both hydrogen abstraction and NIH-shift pathways. Knowledge of these substituent-dependent reaction rates and mechanisms enhances our understanding of the methanotrophic aryl transformation potential and allows for better prediction of the formation of oxidized intermediates by methanotrophic bacteria.