Physicochemical and Biological Properties of Mycobacteriocin M12 Produced by Mycobacterium smegmatis ATCC 25855

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Abstract
A mycobacteriocin (M12) produced by M. smegmatis ATCC 25855 was partially purified by (NH4)2SO4 precipitation followed by DEAE-cellulose chromatography and Sephadex G100 chromatography. Production of M12 was maximal when bacteria were harvested after 3 days of cultivation in liquid medium and disrupted by sonication. The MW of M12, estimated by Sephadex G100 chromatography, was about 85,000. M12 was sensitive to proteolytic enzymes but resistant to DNase and RNase, and was relatively stable to heat treatment, sonication, UV irradiation and pH over the range 4-8. 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. EM 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 Mycobacterium.