Collection, purification and structure elucidation of allelochimcals in Streptomyces sp. 6803

Isolation and identification of allelochemicals is an important step to study allelopathy. Our previous work demonstrated that Streptomyces strain 6803 showed allelopathic effects on both plants and plant fungal pathogens. In this study four macroporous resins (S-8, X-5, AB-8 and HP-20) were used to collect the allelochimcals from the fermentation broth of Streptomyces strain 6803. Among the four resins HP-20 macroporous resin had the highest adsorption capacity for bioactive compounds from the fermentation broth. Three allelochemicals [5,7-dihydroxyflavone (I), 5-hydroxy-7-methoxy-flavone (II) and di (2-ethylhexyl) phthalate] were isolated and purified from the fermentation broth of this strain by column chromatography. Their structure was identified by ESI-MS, ¹HNMR, ¹³CNMR and IR. All isolated compounds showed herbicidal activity. Compound I and II inhibited the root growth of rape (Brassica campestris L.) by 71% and 69% at a concentration of 0.3 mmol/L, respectively. The mean diameter of inhibition zone of compounds I, II and III at 0.3 mmol/L were 22.4, 25.5 and 26.1 mm against the fungal pathogen Fusarium graminearum and 18.9, 16.2 and 15.8 mm against Glomerella cingulata (Stonem), respectively. Our results suggest that HP-20 resin can be efficiently used to collect the allelochemicals from microbial fermentation broth and the compounds I, II and III were responsible for phytotoxic and antifungal activities of Streptomyces strain 6803.