PRODUCTION OF A POTENTIALLY NOVEL ANTIMICROBIAL SUBSTANCE BY BACILLUS-POLYMYXA

A bacterial strain, SCE2, identified as Bacillus polymyxa, produced an anti-microbial substance active against yeasts, fungi and different g enera of Gram-positive and -negative bacteria, in liquid medium and in plate assays. This substance appeared to be an antibiotic different f rom the polymyxin group, mainly because of its action against the majo rity of Gram-positive bacteria tested and its lack of activity against Pseudomonas aeruginosa, a species usually killed by polymyxins. Preli minary characterization showed resistance to heat (65-degrees-C, 2 h), to proteases, trypsin, lysozyme, deoxyribonuclease I, ribonuclease A, phospholipase C, ethanol, acetone, chloroform, ether and to strong al kali treatment (2 M NaOH). The molecular weight was less than 3500. Th e B. polymyxa strain harboured a plasmid that did not correlate with a ntibiotic production; after curing experiments, a derivative strain, S CE2(46), was isolated that lacked the plasmid pFS1, but showed the sam e inhibitory spectrum as the wild-type strain.