Biotransformation of p-xylene and 2,6-dimethylnaphthalene by xylene monooxygenase cloned from a Sphingomonas isolate

Sphingomonas strain ASU1 was isolated from an industrial wastewater bioreactor and grew on 2,6-dimethylnaphthalene (2,6-DMN) as the sole carbon/energy source. The genes for a xylene monooxygenase were cloned from strain ASU1. Expression of the ASU1 xylene monooxygenase was compared to expression of the pWWO xylene monooxygenase in Escherichia coli. Both monooxygenases transformed p-xylene and 2,6-DMN by initially hydroxylating one methyl group. In addition, the ASU1 monooxygenase also hydroxylated the second methyl group on p-xylene and 2,6-DMN whereas the pWWO monooxygenase hydroxylated the second methyl group only on p-xylene. Endogenous E. coli enzymes contributed to further oxidation of the resulting aromatic alcohols to form aromatic carboxylates.