Taxonomy and secondary metabolites of selected marine actinomycetes

Abstract

A total of 75 actinomycetes isolated from marine samples collected from Chumphon, Chonburi, Krabi, Phuket, Prachuap-Khiri-Khan, Samut-Songkhram and Trang provinces were taxonomically studied based on their morphology, chemotaxonomy and 16S rRNA gene sequence analyses. The isolates were identified as members of Family Micromonosporaceae including Jishengella (1 isolate), Micromonospora (25 isolates), Salinispora (13 isolates) and Verrucosispora (2 isolates); Family Nocardiaceae including Nocardia (2 isolates); and Family Streptomycetaceae including Streptomyces (32 isolates). On the basis of phenotypic properties and DNA-DNA hybridization, 4 new actinomycete species were proposed including Streptomyces chumphonensis (isolates KK1-2T and CPB4-7), Streptomyces verrucosisporus (isolates CPB1-1T, CPB2-10, BM1-4, CPB3-1 and CPB1-18), Micromonospora fluostatini (isolate PWB-003T) and Micromonospora sediminis (isolate CH3-3T). Secondary metabolites from culture broth of two new species M. fluostatini PWB-003T, S. chumphonensis KK1-2T and a known species Streptomyces sanyensis C10-9-1 were investigated based on their interesting chemical profiles analyzed by an in-house HPLC database. The chemical structures of isolated secondary metabolites were identified by nuclear magnetic resonance spectroscopy and mass spectrometry. A new diastereomer of fluostatin C, fluorenone, was isolated from M. fluostatini PWB-003T. It showed cytotoxicity against Vero cell line (IC50, 48.5 µg/ml) but did not show cytotoxicity against KB and MCF-7 and antimicrobial activity against Bacillus cereus ATCC 11778, Mycobacterium tuberculosis H37Ra and Pseudomonas aeruginosa K2733. Piericidin A1, a polysubstituted pyridine alkaloid, was obtained from S. chumphonensis KK1-2T. However, the compound at concentration 50µg/ml showed no biological activities such as antimicrobial activity against B. cereus ATCC 11778, M. tuberculosis H37Ra and P. aeruginosa K2733 and cytotoxicity against KB, MCF7 and Vero cell lines. Finally, 4 indolocarbazole alkaloids, staurosporine, staurosporine aglycone, K-252D and 4'-demethylamino-4',5'-dihydroxystaurosporine, were isolated from S. sanyensis C10-9-1. The four alkaloids exhibited cytotoxicity against KB, MCF-7 and Vero cell lines at IC50s ranged from 0.2-45.4 µg/ml. Furthermore, staurosporine, staurosporine aglycone and K-252D exhibited anti-M. tuberculosis H37Ra activity at the MICs ranged from 6.25 to 12.5 µg/ml. In addition, K-252D exhibited anti-B. cereus ATCC 11778 activity (IC50 25.0 µg/ml).