Abstract
The aim of this study was to isolate and identify Actinobacteria from Malaysia mangrove forest and screen them for production of antimicrobial secondary metabolites. Eighty-seven isolates were isolated from soil samples collected at 4 different sites. This is the first report to describe the isolation of Streptomyces, Mycobacterium, Leifsonia, Microbacterium, Sinomonas, Nocardia, Terrabacter, Streptacidiphilus, Micromonospora, Gordonia, and Nocardioides from mangrove in east coast of Malaysia. Of 87 isolates, at least 5 isolates are considered as putative novel taxa. Nine Streptomyces sp. isolates were producing potent antimicrobial secondary metabolites, indicating that Streptomyces isolates are providing high quality metabolites for drug discovery purposes. The discovery of a novel species, Streptomyces pluripotens sp. nov. MUSC 135T that produced potent secondary metabolites inhibiting the growth of MRSA, had provided promising metabolites for drug discovery research. The biosynthetic potential of 87 isolates was investigated by the detection of polyketide synthetase (PKS) and nonribosomal polyketide synthetase (NRPS) genes, the hallmarks of secondary metabolites production. Results showed that many isolates were positive for PKS-I (19.5%), PKS-II (42.5%), and NRPS (5.7%) genes, indicating that mangrove Actinobacteria have significant biosynthetic potential. Our results highlighted that mangrove environment represented a rich reservoir for isolation of Actinobacteria, which are potential sources for discovery of antimicrobial secondary metabolites.
Highlights
Actinobacteria represent a significant component of the microbial population in most soils including the mangrove region [1]
Eighty-seven isolates were isolated from 6 types of isolation media supplemented with cycloheximide, nystatin, and nalidixic acid; these media are, namely, starch casein agar (SCA) (n = 35), International Streptomyces Project (ISP) 2 (n = 18), ISP 7 (n = 18), Actinomycetes isolation agar (AIA) (n = 11), NA (n = 3), and Streptomyces agar (SA) (n = 2)
These results indicated that starch casein agar (SCA) was the most suitable medium for isolating Actinobacteria in this study, and this result is in agreement with others [43]
Summary
Actinobacteria represent a significant component of the microbial population in most soils including the mangrove region [1]. This phylum of bacteria has been extremely useful to the pharmaceutical industry due to their seemingly unlimited capacity to produce secondary metabolites with diverse biological activities and chemical structures [1,2,3,4]. The chances of discovering novel biologically active molecules from various known soil bacteria (including Actinobacteria) have reduced, implying that a saturation effect could be occurring. The isolation of known Actinobacteria such as Streptomyces from various environments was found to be producing similar compounds [6]. The emergence of multidrug resistant pathogenic bacteria such as MRSA and fungus has resulted in critical demand for new natural products and chemical compounds in pharmacology, which in turn has made the exploration of poorly exploited areas such as the mangrove
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