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Applied and Environmental Microbiology, December 2006, p. 7468-7476, Vol. 72, No. 12
0099-2240/06/$08.00+0 doi:10.1128/AEM.01421-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Department of Microbiology, Immunology, and Cancer Biology,1 Department of Biochemistry, Molecular Biology, and Biophysics,2 BioTechnology Institute,3 Center for Microbial and Plant Genomics, University of Minnesota, St. Paul, Minnesota 551084
Received 20 June 2006/ Accepted 18 September 2006
Information on bacterial thioamide metabolism has focused on transformation of the antituberculosis drug ethionamide and related compounds by Mycobacterium tuberculosis. To study this metabolism more generally, a bacterium that grew using thioacetamide as the sole nitrogen source was isolated via enrichment culture. The bacterium was identified as Ralstonia pickettii and designated strain TA. Cells grown on thioacetamide also transformed other thioamide compounds. Transformation of the thioamides tested was dependent on oxygen. During thioamide degradation, sulfur was detected in the medium at the oxidation level of sulfite, further suggesting an oxygenase mechanism. R. pickettii TA did not grow on thiobenzamide as a nitrogen source, but resting cells converted thiobenzamide to benzamide, with thiobenzamide S-oxide and benzonitrile detected as intermediates. Thioacetamide S-oxide was detected as an intermediate during thioacetamide degradation, but the only accumulating metabolite of thioacetamide was identified as 3,5-dimethyl-1,2,4-thiadiazole, a compound shown to derive from spontaneous reaction of thioacetamide and oxygenated thioacetamide species. This dead-end metabolite accounted for only ca. 12% of the metabolized thioacetamide. Neither acetonitrile nor acetamide was detected during thioacetamide degradation, but R. pickettii grew on both compounds as nitrogen and carbon sources. It is proposed that R. pickettii TA degrades thioamides via a mechanism involving consecutive oxygenations of the thioamide sulfur atom.
Published ahead of print on 22 September 2006.
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