Identification of antimicrobial metabolites produced by a potential biocontrol Actinomycete strain A217

To extract and identify the metabolites of strain A217 as well as its antifungal spectrum and control effect on various plant pathogens.

Strain A217 was identified as a Streptomyces sp. which was most similar to Streptomyces lienomycini. An antimicrobial spectrum test indicated that strain A217 inhibited several plant pathogenic fungi and strong antibacterial effect such as Phytophthora capsici, Botrytis cinerea, Sclerotinia sclerotiorum, Fusarium oxysporum, Pseudomonas syringae and Xanthomonas campestris. An in vivo tissue test demonstrated that the fermentation broth of strain A217 exerted therapeutic and protective effects of 49·47 and 61·60% respectively, on S. sclerotiorum. Additionally, the fermentation broth of A217 exerted control effects on walnut black spot disease in walnut leaves and branches amounting to 79·33 and 81·52% respectively. In a pot experiment, the fermentation broth exhibited a stronger protective and control effect (68·29%), as well as better bacteriostatic and disease control effects on Phytophthora blight of pepper, compared with Metalaxyl. Compounds possessing antifungal and antibacterial activities were obtained from the fermentation broth of strain A217, using column chromatography and HPLC. Chemical and structural analyses conducted using MS and nuclear magnetic resonance confirmed that these compounds were 1H-pyrrole-2-carboxylic acid and 1H-pyrrole-2-carboxamide. The EC₅₀ values of compound 1H-pyrrole-2-carboxylic acid1 for S. sclerotiorum and P. capsici were 20·13 and 50·36 μg ml^-1 respectively. Compound 1H-pyrrole-2-carboxamide2 showed significant antibacterial activity against different plant pathogenic bacteria. The MIC values of P. syringae, X. campestris and X. campestris pv. jugiandis were 7·5, 30 and 15·0 μg ml^-1 respectively.

Actinomyces A217 fermentation products have a broad spectrum of bacteriostasis, and have good bacteriostasis activity to many plant pathogenic fungi and bacteria.

The present study revealed a new antimicrobial producing strain of Streptomyces and its potential application as a biological control agent for plant diseases.