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Bioprospecting of mangrove actinomycetes and their antimicrobial potentials
International Islamic University Malaysia
Kulliyyah of of Science, International Islamic University Malaysia
Actinomycetes, a group of Gram-positive bacteria within the order of Actinomycetales are widely distributed in nature. They are renowned for their unrivalled capacity to produce various bioactive metabolites, particularly antibiotics. Even though thousands of antimicrobial agents have been discovered from actinomycetes, these represent only a tiny portion of the entire repertoire. Exploration of poorly explored habitat offers a promising source of bioactive actinomycetes. Less attention has been given in understanding the diversity and biopotential of actinomycetes from mangrove ecosystem. Consequently, the present study was designed to isolate and screen antimicrobial producing actinomycetes from sediment of Kuantan mangrove. A total of 4850 isolates have been successfully enumerated from 7 study sites at Kuantan mangrove forest using various pretreatment procedures and selective isolation media. Wet heat pretreatment (60 ºC for 20 min) yielded the highest number of actinomycetes recovery. Moist heating at mild temperature inhibits the growth of unwanted contamination, while stimulates the colonization of actinomycetes. Actinomycetes from sediment of Kuantan mangrove forest favours isolation medium with high carbon-to-nitrogen ratio. The inorganic salt-starch (ISP4) agar medium displayed the best percentage of recovery (31.1 %), followed by actinomycete isolation (AIA, 24.1 %). A total of 140 representative isolates were selected for further evaluation based on an approach known as dereplication which allows rapid screening of large ambiguous actinomycetes collection. Determination on the antimicrobial activity of the isolates were conducted in a series of susceptibility tests against 5 test organisms. Preliminary screening revealed that 55.7 % of the total representative isolates possess antagonistic potential against at least one test organisms. The bioactive isolates were subjected to liquid fermentation and antimicrobial activity of their crude ethyl acetate extracts were evaluated using disc diffusion assay. Only 47 isolates demonstrated inhibitory activity with members of genus Streptomyces being the most frequent antimicrobial metabolite producers. Streptomyces sp. K1–01 and Streptomyces sp. K2–03 are the most promising isolates as they demonstrated various degree of antimicrobial activity against all test organisms, suggesting broad spectrum nature of the antimicrobial compounds they produced. Additional evaluation to identify potentially bioactive isolates were also carried out by detecting the presence of biosynthetic genes designated as non-ribosomal peptide synthetase (NRPS) and type-I polyketide synthase (PKS-I). Members of rare genera including Micromonospora sp. (K1–02, K3–13, K7–04), Pseudonocardia sp. (K3–12, K4–16, K7–13), Verrucosispora sp. (K2–04, K7–12), Nocardiopsis sp. K4–09 and Actinophytocola sp. K4–08 also displayed promising antimicrobial potential. Characterization of cultivable actinomycetes provides information on the diversity of Kuantan mangrove actinomycetes. Dietzia, Gordonia, Micrococcus, Mycobacterium, Nocardia, Saccharopolyspora and Rhodococcus can be added to the list of genera isolated from this ecological niche, providing a solid evidence that considerable diversity of actinomycetes are distributed within Kuantan mangrove forest. The present finding suggested that sediment of Kuantan mangrove forest could serve as an important source for high taxonomic diversity of actinomycetes with interesting biosynthetic capabilities for drug discovery program.
Thesis (MSBTS)--International Islamic University Malaysia, 2016
Includes bibliographical references (leaves 124-148).