The bacterial biodegradation of a secondary sulphonate, sulphosuccinate, has been shown to occur by direct desulphonation. A bacterium, designated 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 CO release from specifically radiolabelled sulpho[1,4C]succinate and sulpho[2,3-C]succinate, which were synthesized from the corresponding maleic anhydrides. When each radiolabelled compound was incubated separately with washed-cell suspensions of BS1, sulphite was released before CO, as shown by chemical assay and radiorespirometry, respectively. Differences in the kinetics and extent of CO release from the 1,4- and 2,3-labelled substrates were consistent with entry of the intact C 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.


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