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Biodegradation of sulphosuccinate: direct desulphonation of a secondary sulphonate

¹School of Molecular and Medical Biosciences, Biochemistry Unit, University of Wales Cardiff, PO Box 911, Cardiff CF1 3US, UK
²Unilever Research, Port Sunlight Laboratory, Bebington, Wirral, Merseyside L63 3JW, UK

Author for correspondence: Graham F. White. Tel: +44 222 874188. Fax: +44 222 874116. e-mail: whitegf1@cardiff.ac.uk

ABSTRACT

The bacterial biodegradation of a secondary sulphonate, sulphosuccinate, has been shown to occur by direct desulphonation. A bacterium, designated Pseudomonas sp. BS1, was isolated from activated sewage sludge, for its capacity to grow on sulphosuccinate as the sole source of carbon and energy. Cultures grown on sulphosuccinate were able to convert this substrate to sulphite which was subsequently oxidized rapidly to sulphate. The sequence of desulphonation and carbon-chain catabolism of sulphosuccinate was determined from measurements of the kinetics of sulphite and ¹⁴CO₂ release from specifically radiolabelled sulpho[1,4^-14C]succinate and sulpho[2,3-¹⁴C]succinate, which were synthesized from the corresponding maleic anhydrides. When each radiolabelled compound was incubated separately with washed-cell suspensions of Pseudomonas BS1, sulphite was released before ¹⁴CO₂, as shown by chemical assay and radiorespirometry, respectively. Differences in the kinetics and extent of ¹⁴CO₂ release from the 1,4- and 2,3-labelled substrates were consistent with entry of the intact C₄ chain into the citric acid cycle. When carrier oxaloacetate was added to incubation mixtures containing resting-cell suspensions and radiolabelled sulphosuccinate, a radiolabelled metabolite with the same HPLC retention time as oxaloacetate accumulated. No radioactive metabolites accumulated when carrier oxaloacetate was replaced with succinate, fumarate or malate. Collectively, the data indicated co-production of sulphite and oxaloacetate from sulphosuccinate, which is interpreted in terms of an oxidative desulphonation mechanism.