1. An organism was isolated by enrichment culture that was capable of using thiophen-2-carboxylate as sole source of carbon, energy and sulphur for growth. 2. Analysis of the cellular protein after growth of the organism on thiophen-2-[14C]carboxylate showed that only glutamate, proline and arginine were labelled. All the radioactivity in the glutamate was confined to C-1. 3. In the presence of 2.1 mm-arsenite, suspensions of the organism converted thiophen-2-[14C]carboxylate into 14C-labelled 2-oxoglutarate which had the same specific radioactivity as the starting material. 4. Cell-free extracts of the organism catalysed the release of 14CO2 from thiophen-2-[14C]carboxylate. This activity was largely dependent on the presence of ATP and CoA and was stimulated by NAD+ and Mg2+. Inclusion of hydroxylamine resulted in the appearance of thiophen-2-carbohydroxamic acid, indicating that the ATP and CoA were involved in the formation of the CoA ester of thiophen-2-carboxylate. 5. High-speed centrifuging of cell-free extracts resulted in supernatants with decreased thiophen-2-carboxylate-degrading activity. Activity was restored by the addition of the high-speed pellet or by Methylene Blue. 6. The metabolism of the CoA ester of thiophen-2-carboxylate by cell-free extracts could be linked to the anaerobic reduction of Methylene Blue. 7. The sulphur atom of the thiophen nucleus was converted into sulphate by growing cultures and resting suspensions of the organism. 8. A degradative pathway is proposed involving the hydroxylation (at C-5) of the CoA ester of thiophen-2-carboxylate followed by further metabolism to 2-oxoglutarate and sulphate.

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