Biodegradation of dibenzothiophene by a nodulating isolate of Rhizobium meliloti

Rhizobium meliloti Orange 1 was isolated from aerobic sediments of a drainage ditch receiving oil refinery leakage. This bacterium has been shown to be capable of growing on dibenzothiophene as the sole carbon and energy source. This strain can also efficaciously nodulate alfalfa plants. In cultures with dibenzothiophene, Orange 1 produces six degradation intermediates. By means of analyses with UV-visible and GC-MS spectrometry, as well as nuclear magnetic resonance spectroscopy, three of these products were identified as 3-hydroxy-2-formyl-benzothiophene (product A), benzothienopyran-2-one (product B'), and dibenzothiophene-5-oxide (product D). This suggests that R. meliloti Orange 1 metabolizes dibenzothiophene via oxidative cleavage of the aromatic ring with a mechanism analogous to that described for naphthalene degradation.