Taxonomy and secondary metabolites of selected endophytic actinomycete strains

Abstract

A total of 50 endophytic actinomycetes isolated from fourteen plant species collected from six provinces of Thailand including Bangkok, Chachoengsao, Chiang Mai, Nakhon Pathom, Prachinburi and Suphan Buri were taxonomically studied relied on their phenotypic and chemotaxonomic characteristics, and the 16S rRNA gene sequence analysis. The isolates were identified as members of the family Streptomycetaceae involving Streptomyces (22 isolates), and the family Micromonosporaceae including Micromonospora (25 isolates), Plantactinospora (1 isolate) and Polymorphospora (1 isolate). Based on phenotypic characteristics, whole genome sequence analysis and DNA-DNA hybridization, 5 novel actinomycete species were proposed consisting of Micromonospora globbae (strain WPS1-2T), Micromonospora azadirachtae (strain AZ1-19T), Micromonospora radicis (strain AZ1-13T), Micromonospora musae (strain MS1-9T and NGC1-4) and Streptomyces endoradicus (strain DS1-2T and AZ1-7).

Secondary metabolites from culture broth of Streptomyces pseudovenezuelae SKH1-2 and Streptomyces aculeolatus MS1-6 were studied based on their interested chemical profiles analyzed by the in-house HPLC chemical database. The chemical structures of the isolated secondary metabolites were identified using nuclear magnetic resonance spectroscopy (NMR) and mass spectroscopy. Chartreusin and lumichrome, polyketide, were isolated from S. pseudovenezuelae SKH1-2T. Chartreusin exhibited antimicrobial activity against Bacillus subtilis ATCC 6633, Kocuria rhizophila ATCC 9341 and Staphylococcus aureus ATCC 6538p with MIC values of 3.1, 1.6 and 12.5 ug/mL, respectively, whilst lumichrome did not show any antimicrobial activity. In addition, a naphthoquinone, arromycin, and one derivative of salicylic acid, salaceyin A, were isolated from S. aculeolatus MS1-6. Arromycin has been reported as anti-Gram-positive bacteria such as B. subtilis, S. aureus, Listeria ivanovii and Enterococcus faecium while salaceyin A has the anti-phytopathogenic fungi including Cladosporium cucumerinum, Colletotrichum orbiculare and Phytophthora capsici.