Isolation, antimicrobial screening and identification of actinomycetes from mangrove sediments of Tanjung Lumpur, Kuantan, Pahang

Abstract

Actinomycetes are renowned as a rich source of bioactive molecules. However, the commercially potent secondary metabolites from well-known actinomycetes are difficult to discover due to the practice of screening that is leading to rediscovery of known bioactive compounds, thereby, emphasizing the need to isolate undiscovered actinomycetes. Mangroves are highly productive ecosystem though less attention has been given into the diversity of actinomycetes present in mangrove sediment particularly in Malaysia. Therefore, the objectives of this study were to isolate, screen and identify antimicrobial producing actinomycetes from sediment samples in Tanjung Lumpur mangrove. Sediments from five different sites at Tanjung Lumpur mangrove were collected and selectively pre-treated. The pretreated sediments were diluted and plated onto eight different selective media. Pretreatment of wet heat with seawater was the most effective method for the isolation of actinomycetes as it yielded a maximum of 105 isolates and IM7 was the most suitable medium for actinomycete isolation with highest percentage of recovery (31%). A total of 172 potential actinomycetes were isolated from all the media. Antimicrobial activities of the selected isolates were checked against 8 test microorganisms using primary and secondary screening. In primary screening, of 61 isolates, 43 isolates showed antimicrobial activities against one or more test microorganisms. Isolate IIUM B21 and IIUM B31 showed inhibitory activity against all the test microorganisms. They were found to have good activity against B. subtilis, S. pyogenes and C. albicans. Forty three actinomycete isolates showing positive antimicrobial activity in the primary screening were subjected to secondary screening assay. In this test, only 12 isolates showed antimicrobial activity at least to one test microorganisms. Twelve isolates were randomly selected for identification based on partial sequences of 16S rRNA gene. Eight isolates were found belong to the genus Streptomyces, 2 isolates belong to the genus Micromonospora and 2 isolates were identified as Rhodococcus species. A phylogenetic tree was constructed. The 12 identified isolates showed different morphologies on the 8 selective media. These findings revealed the potential of mangrove sediment of Tanjung Lumpur as an important source of actinomycetes with biosynthetic capabilities which might be beneficial to pharmaceutical industries.