title: Identification of disulfides from the biodegradation of dibenzothiophene.
abstract: Several investigations have identified benzothiophene-2,3-dione in the organic solvent extracts of acidified cultures degrading dibenzothiophene via the Kodama pathway. In solution at neutral pH, the 2,3-dione exists as 2-mercaptophenylglyoxylate, which cyclizes upon acidification and is extracted as the 2,3-dione. The fate of these compounds in microbial cultures has never been determined. This study investigated the abiotic reactions of 2-mercaptophenylglyoxylate incubated aerobically in mineral salts medium at neutral pH. Oxidation led to the formation of 2-oxo-2-(2-thiophenyl)ethanoic acid disulfide, formed from two molecules of 2-mercaptophenylglyoxylate. Two sequential abiotic, net losses of both a carbon and an oxygen atom produced two additional disulfides, 2-oxo-2-(2-thiophenyl)ethanoic acid 2-benzoic acid disulfide and 2,2'-dithiosalicylic acid. The methods developed to extract and detect these three disulfides were then used for the analysis of a culture of Pseudomonas sp. strain BT1d grown on dibenzothiophene as its sole carbon and energy source. All three of the disulfides were detected, indicating that 2-mercaptophenylglyoxylate is an important, short-lived intermediate in the breakdown of dibenzothiophene via the Kodama pathway. The disulfides eluded previous investigations because of (i) their high polarity, being dicarboxylic acids; (ii) the need to lower the pH of the aqueous medium to <1 to extract them into an organic solvent such as dichloromethane; (iii) their poor solubility in organic solvents, (iv) their removal from organic extracts of cultures during filtration through the commonly used drying agent anhydrous sodium sulfate; and (v) their high molecular masses (362, 334, and 306 Da) compared to that of dibenzothiophene (184 Da).
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
authors.forename: D C
authors.initials: DC
authors.lastname: Bressler
authors.forename: P M
authors.initials: PM
authors.lastname: Fedorak
mesh_terms: D001673:Biodegradation, Environmental; D003470:Culture Media; D004220:Disulfides / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D010084:Oxidation-Reduction; D011549:Pseudomonas / Q000254:growth & development / Q000378:metabolism; D013876:Thiophenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D003470:Culture Media; D004220:Disulfides; D013876:Thiophenes; C016366:dibenzothiophene