Antitumour and antimicrobial activities of endophytic streptomycetes from pharmaceutical plants in rainforest

Aims:  The aim of this study was to screen antitumour and antimicrobial activities of endophytic actinomycetes isolated from pharmaceutical plants in rainforest in Yunnan province, China. Methods and Results:  Antitumour activity was studied by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and antimicrobial activity was determined by agar well diffusion method. The high bioactive endophytic isolates were identified and further investigated for the presence of polyketide synthases (PKS-I, PKS-II) and nonribosomal peptide synthetases (NRPS) sequences by specific amplification. The molecular identification confirmed that the 41 isolates showed significant activities were members of the genus Streptomyces. Among them, 31·7% of endophytic streptomycete cultures were cytotoxic against A549 cells, 29·3% against HL-60 cells, 85·4% against BEL-7404 cells, 90·2% against P388D1 cells, 65·9% were active against Escherichia coli, 24·4% against Staphylococcus aureus, 31·7% against Staphylococcus epidermidis, 12·2% against Candida albicans and no strain displayed antagonistic activity against Klebsiella pneumoniae. High frequencies of positive PCR amplification were obtained for PKS-I (34·1%), PKS-II (63·4%) and NRPS (61·0%) biosynthetic systems. Conclusions:  Many endophytic streptomycetes isolated from pharmaceutical plants in rainforest possess remarkable and diverse antitumour and antimicrobial bioactivities. Significance and Impact of the Study:  These endophytic streptomycetes are precious resources obtained from rainforests, and they could be a promising source for bioactive agents.