Bacterial transformations of 1,2,3,4-tetrahydrodibenzothiophene and dibenzothiophene

Abstract

The transformations of 1,2,3,4-tetrahydrodibenzothiophene (THDBT) were investigated with pure cultures of hydrocarbon-degrading bacteria. Metabolites were extracted from cultures with dichloromethane (DCM) and analyzed by gas chromatography (GC) with flame photometric, mass, and Fourier transform infrared detectors. Three 1-methylnaphthalene (1-MN)-utilizing Pseudomonas strains oxidized the sulfur atom of THDBT to give the sulfoxide and sulfone. They also degraded the benzene ring to yield 3-hydroxy-2-formyl-4,5,6,7-tetrahydrobenzothiophene. A cell suspension of a cyclohexane-degrading bacterium oxidized the alicyclic ring to give a hydroxy-substituted THDBT and a ketone, and it oxidized the aromatic ring to give a phenol, but no ring cleavage products were detected. GC analyses with an atomic emission detector, using the sulfur-selective mode, were used to quantify the transformation products from THDBT and dibenzothiophene (DBT). The cyclohexane degrader oxidized 19% of the THDBT to three metabolites. The cometabolism of THDBT and DBT by the three 1-MN-grown Pseudomonas strains resulted in a much greater depletion of the condensed thiophenes than could be accounted for in the metabolites detected by GC analysis, but there was no evidence of sulfate release from DBT. These 1-MN-grown strains transiently accumulated 3-hydroxy-2-formylbenzothiophene (HFBT) from DBT, but it was subsequently degraded. On the other hand, Pseudomonas strain BT1d, which was maintained on DBT as a sole carbon source, accumulated 52% of the sulfur from DBT as HFBT over 7 days, and, in total, 82% of the sulfur from DBT was accounted for by the GC method used. Lyophilization of cultures grown on 1-MN with DBT and methyl esterification of the residues gave improved recoveries of total sulfur over that obtained by DCM extraction and GC analysis. This suggested that the further degradation of HFBT by these cultures leads to the formation of organosulfur compounds that are too polar to be extracted with DCM. We believe that this is the first attempt to quantify the products of DBT degradation by the so-called Kodama pathway.