Purification and characterization of salvianolic acid B from Streptomyces sp. M4 possessing antifungal activity against fungal phytopathogens

The emergence of resistance among fungal phytopathogens poses a biggest threat across the world. Streptomyces are a group of spore-forming Gram + ve bacteria and prolific producers of secondary bioactive metabolites which have been used as biocontrol agents against phytopathogens and also known for plant growth promotion. The current study identified a potent isolate M4 from soil with broad spectrum antifungal activity against different fungal phytopathogens. The isolate was identified as a Streptomyces sp. on the basis of cultural, morphological, physiological, biochemical and phylogenetic characteristics. 16S rRNA gene sequence of M4 showed 100 % similarity with three Streptomyces spp. i.e. Streptomyces plicatus NBRC 13071 T (AB184291), Streptomyces rochei NBRC 12908 T AB184237 and Streptomyces enissocaesilis NRRL-B-16365 T (DQ026641). However, phenotypic and phylogenetic analysis concluded that M4 represents a novel sp. within the genus Streptomyces. One of the two antifungal compounds purified from Streptomyces M4 was identified as salvianolic acid B. To our knowledge, the present study is the first work reporting purification and characterization of salvianolic acid B from Streptomyces and its broad spectrum antifungal activity against different fungal phytopathogens viz. Alternaria spp., Fusarium spp., Colletotrichum spp., Cladosporium herbarum and Botrytis cineria. Salvianolic acid B was found to be photostable, thermostable (up to 70 degrees C) and non-mutagenic in nature and might be developed as safe biofungicide to control phytopathogens.