Summary: A mycobacteriocin (M12) produced by ATCC 25855 was partially purified by ammonium sulphate precipitation followed by DEAE-cellulose chromatography and Sephadex G100 chromatography. Production of M12 was maximal when bacteria were harvested after 3 d cultivation in liquid medium and disrupted by sonication. The molecular weight of M12, estimated by Sephadex G100 chromatography, was about 85000. M12 was sensitive to proteolytic enzymes but resistant to DNAase and RNAase, and was relatively stable to heat treatment, sonication, ultraviolet irradiation and pH over the range 4 to 8. When sensitive bacteria were exposed to the mycobacteriocin, the number of viable cells began to decrease after about 6 h incubation. The killing curve of M12 thus appeared to be a multiple-hit curve. Electron microscopic observation revealed that the mycobacteriocin induced morphological changes in the cells: these were partial loss of ribosomes, enlargement of lipoidal inclusion bodies and thickening of the cell envelope. The activity spectrum of M12 was restricted to the genus .


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