SPECIFICITY OF IMPROVED METHODS FOR MYCOBACTIN BIOASSAY BY ARTHROBACTER TERREGENS

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Abstract
Arthrobacter terregens was used to assay mycobactin, a growth factor for Mycobacterium paratuberculosis. Improved techniques permit the assay of mycobactinwithin 3 to 4 days by agar-plate or liquid-medium methods. For the agarplate method, A. terregens gave linear increases in zonal growth at mycobactin concentrations of 0.07 to 0.30 [mu]g per spot; for the liquid-medium method, linear increases in turbidimetric growth occurred at 0.05 to 0.27 [mu]g/ml. Specificity studies show that the mycobactin hydrolytic products, cobactin and mycobactic acid, function as growth stimulators, but the high concentrations required would produce only minimal interference in mycobactin assays. Furthermore, the response to mycobactic acid is characterized by a delayed response of 3 days. Various synthetic hydroxylamine-containing compounds and metal-chelating agents cannot replace the biological activity of mycobactin. Diacetyl-mycobactin is 7.4 times more effective than mycobactin as a growth stimulator.