Biodegradation of metabolites from condensed thiophenes found in petroleum

Condensed thiophenes comprise a small but significant portion of fossil fuels and their derivatives. Analysis of samples recovered from environments contaminated with petroleum or fossil fuel derivatives frequently demonstrates the persistence of these compounds. Representative model compounds include benzo[b]thiophene and dibenzothiophene. Previous work has shown the loss of these compounds resulting in the formation of oxidized metabolites. This study focussed on the aerobic biodegradation of some of these condensed thiophene metabolites. Compounds studied included both biodegradation metabolites of dibenzothiophene (including benzothiophene-2,3-dione and 3-hydroxy-2-formylbenzothiophene) and metabolites of benzothiophene and methyl benzothiophenes (benzothiophene sulfone, 3- and 5-methylbenzothiophene sulfones and benzothiophene-2,3-dione).; Pseudonocardia strain DB1 was isolated based upon its ability to utilize benzothiophene sulfone as sole carbon, energy and sulfur source. It was shown to utilize 3- and 5-methylbenzothiophenes as sole carbon, energy and sulfur sources as well as metabolize the analog 5-fluorobenzothiophene sulfone when grown on benzothiophene sulfone. Strain DB1 mineralized the sulfones demonstrating large amounts of carbon dioxide, sulfate, and fluoride release. 2,3-Dihydro-2-hydroxybenzothiophene sulfone was observed as a metabolite of benzothiophene sulfone and 5-fluoro-2,3-dihydro-2-hydroxybenzothiophene sulfone was identified as a metabolite of 5-fluorobenzothiophene sulfone. Benzonaphthothiophene sulfone was also observed as an abiotic condensation product of benzothiophene sulfone.; This dissertation revealed that benzothiophene-2,3-dione and 3-hydroxy-2-formylbenzothiophene were both chemically unstable and were observed to undergo condensation reactions. At neutral pH, benzothiophene-2,3-dione undergos an abiotic ring opening to form 2-mercaptophenylglyoxylate. This open ring compound was observed to under go a sulfur oxidation to yield a large disulfide compound which subsequently decarbonylated twice, with observable intermediates, to form 2,2′ -dithiosalicylic acid. Preliminary studies revealed that the 2,2 ′-dithiosalicylic acid could be biodegraded by a mixed bacterial population.; 3-Hydroxy-2-formylbenzothiophene, when protonated, was observed to undergo a condensation reaction resulting in the formation of cis- and trans-thioindigo. 3-Hydroxy2-formylbenzothiophene was biodegraded by a mixed bacterial culture, and that benzothiophene-2,3-dione (or 2-mercaptophenylglyoxylate) accumulated in culture supernatants.; The studies described in this dissertation gathered significant evidence that condensation reactions may play a major role in deciding the final fate of carbon and sulfur from condensed thiophenes after biodegradation. It is suggested that future biodegradation investigations seriously consider the search for products with significantly higher molecular weights than starting substrates.