LAUSR

Streptomyces spp. are Gram-positive bacteria well-known for their ability to produce antibiotics and other metabolites, but few studies on bacteriocins produced by these bacteria have been reported. We tested eight Streptomyces strains against different pathogenic bacteria, and selected S. griseus, S. nigrescens, S. bottroprensis, and S. violaceoruber for further study based on their inhibitory effects against bacteria, including human pathogens. S. bottropensis reached its highest activity at 312 h and was higher than the activities of S. violaceoruber and S. nigrescens. The best condition for bacteriocin precipitation was using diammonium sulfate at 50% saturation. Bacteriocins were susceptible to proteinase treatments and stable at high temperature (up to 100 °C). The highest inhibitory activities were observed between pH 5 and 6. Cross-activity assays indicated that each Streptomyces strain produced different bacteriocins. When preparations of S. griseus and S. nigrescens were subjected to SDS-PAGE, bands of inhibition were observed in the gel overlay assay at a position corresponding to ~ 2 and 3 kDa, respectively, suggesting that both strains are potential sources for novel bacteriocins.