| The aerobic microbial metabolism of benzothiophene, six isomers of each of methyl- and dimethylbenzothiophene, dibenzothiophene, three isomers of dimethyldibenzothiophene, 1,2,3,4-tetrahydrodibenzothiophene, naphtho(2,1-b) thiophene, naphtho (2,3-b) thiophene, and 1-methylnaphtho (2,1-b) thiophene was studied. All 21 of these compounds are found in petroleum or synthetic fuels, but only four of them are commercially available. The other condensed thiophenes were synthesized by Dr. J. T. Andersson (University of Munster), for use in biodegradation studies. The study of methyl-substituted condensed thiophenes was motivated by recent research which showed that their resistance to biodegradation increases with increasing methyl-substitution.; The objective was to identify metabolites in pure cultures of aromatic hydrocarbon-degrading Pseudomonas spp. incubated in mineral medium in the presence of an aromatic growth substrate (i.e. 1-methylnaphthalene) and a pure condensed thiophene. As well, some studies investigated the biodegradation of condensed thiophenes in mineral medium with petroleum or the aromatic fraction of petroleum as the growth substrate for mixed cultures of petroleum-degrading. bacteria or for cultures inoculated with an environmental sample (i.e. river water). These studies were done because mixed populations generally have greater degradative potential and more closely-approximate the situation of an actual oil-contaminated environment. After appropriate incubation times, the cultures were extracted with organic solvent to recover substrates and products, and extracts were analyzed by gas chromatography with flame photometric, mass, and Fourier transform infrared detectors. This enabled the identification of biotransformation products, whose structures frequently were verified by comparisons with synthesized authentic standards. Other identifications required the purification of metabolites and analysis by nuclear magnetic resonance spectrometry. Gas chromatography analysis with an atomic emission detector, which gives a linear response to sulfur in all organic forms, was used to quantify some of the observed metabolites.; By these methods, over 80 metabolites of the condensed thiophenes listed above were identified. These include sulfoxides, sulfones, hydroxy- and carboxyl-substituted benzothiophenes, hydroxy-substituted dibenzothiophenes, and substituted benzothiophene-2,3-diones and 3-hydroxy-2-formylbenzothiophenes. Benzonaphthothiophenes were also observed to form by an abiotic condensation of microbially-produced benzothiophene sulfoxides. |
