Amide groups are common in biological molecules (e.g. peptide bonds), but thioamides are rare. Thioamide groups are found naturally in the copper-chelating compound methanobactin described in Methylosinus trichosporium OB3b ([http://www.ncbi.nlm.nih.gov/pubmed/15361623|Kim et al., 2004]). The antibiotic sulfinemycin, produced by Streptomyces albus NRRL 3384, has a primary thioamide S-oxide moiety ([http://www.ncbi.nlm.nih.gov/pubmed/7730167|Lee et al., 1995]). Thioamide compounds such as 2-ethyl-4-pyridinecarbothioamide (ethionamide) are important second-line drugs in the treatment of multi-drug resistant Mycobacterium tuberculosis and M. leprae ([http://www.ncbi.nlm.nih.gov/pubmed/12164478|Schroeder et al., 2002]; [http://www.ncbi.nlm.nih.gov/pubmed/3910748|Shepard et al., 1985]). Toxicity of thioamides in mammals and Mycobacterium spp. is dependent on metabolic activation of the compounds via sequential oxygenations of the thioamide sulfur atom by flavoprotein monooygenases or cytochromes P450 ([http://www.ncbi.nlm.nih.gov/pubmed/10944230|Debarber et al., 2000]; [http://www.ncbi.nlm.nih.gov/pubmed/10900221|Wang et al., 2000]; [http://www.ncbi.nlm.nih.gov/pubmed/28917|Porter and Neal, 1978]). Thioamide S-oxides are not toxic without further oxygenation and investigators have proposed that thioamide S,S-dioxides (which have not been isolated) or further oxidized species exert the observed toxic effects ([http://www.ncbi.nlm.nih.gov/pubmed/11823459|Vannelli et al., 2002]; [http://www.ncbi.nlm.nih.gov/pubmed/6135576|Hanzlik and Cashman, 1983]; [http://www.ncbi.nlm.nih.gov/pubmed/28917|Porter and Neal, 1978]). This activity results in elimination of the thioamide sulfur and formation of nitrile and/or amide derivatives ([http://www.ncbi.nlm.nih.gov/pubmed/11823459|Vannelli et al., 2002]; [http://www.ncbi.nlm.nih.gov/pubmed/10944230|Debarber et al., 2000]; [http://www.ncbi.nlm.nih.gov/pubmed/28917|Porter and Neal, 1978]). EtaA, a thioamide-oxidizing flavin monooxygenase in Mycobacterium tuberculosis, converted thiobenzamide to thiobenzamide S-oxide and benzamide ([http://www.ncbi.nlm.nih.gov/pubmed/11823459|Vannelli et al., 2002]). Ralstonia pickettii TA, which can grow using thioacetamide as a sole source of nitrogen and carbon ([http://www.ncbi.nlm.nih.gov/pubmed/16997975|Dodge et al., 2006]), converted thiobenzamide sequentially to thiobenzamide S-oxide, benzonitrile, and benzamide. Whole M. tuberculosis cells metabolized ethionamide similarly through the corresponding S-oxide, nitrile, and amide derivatives ([http://www.ncbi.nlm.nih.gov/pubmed/10944230|Debarber et al., 2000]). Sulfur eliminated from thiobenzamide by R. pickettii TA was detected in the medium as sulfur dioxide/sulfite. Release of sulfur at this oxidation state from thiobezamide S,S-dioxide, the proposed intermediate after thiobenzamide S-oxide, requires an additional two-electron oxidation. The mechanisms of this additional sulfur oxidation and benzonitrile formation are unknown.