Evaluation of antimicrobial activity some of marine Streptomyces sp. against three plant pathogens

In recent years, application of secondary metabolites such as antibiotics has been considered as a biological control method for plant pathogens. This study aimed to isolate, identify and evaluate the antimicrobial activity of Streptomyces species in Oman Sea against three plant pathogens including Fusarium oxysporum, Xanthomonas campestris and Erwinia amylovora. The Streptomyces strains were isolated on different media including starch casein agar, glycerol glycine agar and starch nitrate agar with different NaCl concentration. Preliminary antimicrobial activity was investigated using cross streak method and evaluated by measuring the zone of growth inhibition against plant pathogens. Ninety percent of the strains were able to inhibit the growth of X. campestris strain and the highest inhibition zone was 15±1 mm. Two strains, AC275 and AC130 were selected to extract the antimicrobial compound. The isolates were cultured in different seed cultures and fermentation media. The application of different fermentation media shows that glycerol and soybeans cultures increase inhibition zone. Based on 16S rRNA gene analysis, two strains were belonged to Streptomyces sp. The organic solvents including dichloromethane, chloroform and ethyl acetate were used in order to extract the antimicrobial compound. Dichloromethane in AC130 and chloroform in AC275 were more effective than other solvents by creating an inhibition zone of 21 and 25 mm respectively. This study shows that the Streptomyces species in less explored marine environment have the ability to control plant pathogenic bacteria.