Catalyzes the first step of the '4S' desulfurization pathway that removes covalently bound sulfur from dibenzothiophene (DBT) without breaking carbon-carbon bonds. Sulfur dioxygenase which converts DBT to DBT-sulfone (DBTO2 or DBT 5,5-dioxide) in a stepwise manner. In (PubMed:7961424) DBTO (dibenzothiophene-5-oxide) was reported not to be a substrate, in (PubMed:7574582, PubMed:9634856, PubMed:8824615 and PubMed:9308179) it is reported to be a substrate (PubMed:7961424, PubMed:7574582, PubMed:9634856, PubMed:8824615, PubMed:9308179). Can also use benzyl sulfide and benzyl sulfoxide as substrates, although benzyl sulfoxide is a poor substrate (PubMed:8824615). The pathway substrate specificity has been augmented using mutagenesis, however no mutations allowed use of alkylated thiophenes (PubMed:11823208). dibenzothiophene + 2 FMNH2 + 2 O2 = dibenzothiophene 5,5-dioxide + 2 FMN + 2 H(+) + 2 H2O dibenzothiophene + FMNH2 + O2 = dibenzothiophene 5-oxide + FMN + H(+) + H2O dibenzothiophene 5-oxide + FMNH2 + O2 = dibenzothiophene 5,5-dioxide + FMN + H(+) + H2O Addition of FAD increases DBTO2 production in cell lysates. Reduced flavin is provided by flavin reductase DszD; in vitro NADPH and FAD are not substrates. Sulfur metabolism; dibenzothiophene degradation. Homotetramer (PubMed:9634856). Homodimer (PubMed:8824615). Expressed during growth on DBT or DMSO as sole sulfur source (at protein level) (PubMed:8932295). Part of the probable dszA-dszB-dszC operon (Probable). Desulfurization is repressed by sulfate, cysteine and methionine (PubMed:7574582, PubMed:8932295). The lid loop assumes one of 2 conformations allowing opening and closing of the active site. No detectable desulfurization activity on DBT. Can be used to remove sulfur from polycyclic aromatic sulfur compounds found in gasoline and diesel (biodesulfurization), which are a considerable source of pollution. In addition it may be possible to engineer the operon to make specialty chemicals. Belongs to the DszC flavin monooxygenase family.