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. 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 Reduced flavin is provided by flavin reductase DszD. Sulfur metabolism; dibenzothiophene degradation. Homotetramer formed of a dimer of dimers. The lid loop assumes one of 2 conformations allowing opening and closing of the active site; in the 3D structure one dimer is open while the other is closed (PubMed:24470304). Another structure with FMN (3X0Y) proposes a different lid loop that may interact with the loop predicted here (By similarity). Can be used to remove sulfur from polycyclic aromatic sulfur compounds found in gasoline and diesel (biodesulfurization), which are a considerable source of pollution. As the substrates are not very soluble in conventional media, biphasic systems may help improve catalysis. Expression of dszD-dszA-dszB-dszC (cloned in this order) in organic-solvent-tolerant P.putida strain Idaho allows P.putida to grow on 10% p-xylene with DBT as the sole sulfur source. In this P.putida strain 97% of DBT was degraded, 71% of 4,6-dimethyldibenzothiophene and about 50% of 3-methyldibenzothiophene or 4-methyldibenzothiophene was degraded in the presence of 10% p-xylene. Degradation of DBT in the presence of 10% of other organic solvents was tested; when grown in dodecane, cyclohexane or heptanol bacteria metabolized DBT as well as p-xylene, while other organic solvents degraded DBT slightly less well. Belongs to the DszC flavin monooxygenase family.