Isolation and Characterization of Novel Marine-Derived Actinomycete Taxa Rich in Bioactive Metabolites

Abstract

A unique selective enrichment procedure has resulted in the isolation and identification of two new genera of marine-derived actinobacteria. Approximately 90% of the microorganisms cultured by using the presented method were from the prospective new genera, a result indicative of its high selectivity. In this study, 102 actinomycetes were isolated from subtidal marine sediments collected from the Bismarck Sea and the Solomon Sea off the coast of Papua New Guinea. A combination of physiological parameters, chemotaxonomic characteristics, distinguishing 16S rRNA gene sequences, and phylogenetic analysis based on 16S rRNA genes provided strong evidence for the two new genera (represented by strains of the PNG1 clade and strain UMM518) within the family Micromonosporaceae. Biological activity testing of fermentation products from the new marine-derived actinomycetes revealed that several had activities against multidrug-resistant grampositive pathogens, malignant cells, and vaccinia virus replication.The order Actinomycetales is composed of approximately 80 genera, nearly all from terrestrial soils, where they live primarily as saprophytes (30,36). All members of the order are characterized in part by their high GϩC DNA content, and most exhibit a highly differentiated developmental life cycle (30). Several recent systematic reevaluations of the order reflected more closely the integration of molecular data (16S rRNA gene sequences). This reorganization resulted in the placement of the two most prolific producers of secondary metabolites, Streptomyces and Micromonospora, in the families Streptomycetaceae and Micromonosporaceae, respectively (30).The diversity of actinomycete secondary metabolites is unrivaled and unmatched in medical significance. Structurally and functionally diverse bioactive compounds have also been isolated from other prokaryotes, including members of the myxobacteria (e.g., Sorangium) and cyanobacteria (e.g., Nostoc), as antibiotics with antimicrobial, antiviral, and antitumor activities (16,21,24,25). Recently, the rate of discovery of new compounds from existing genera obtained from terrestrial sources has decreased, while the rate of reisolation of known compounds has increased. Moreover, the rise in the number of drug-resistant pathogens and the limited success of strategies such as combinatorial chemistry in providing new agents indicate an uncertain forecast for future antimicrobial therapy (17, 18). Thus, it is critical that new groups of microbes from unexplored habitats be pursued as sources of novel antibiotics and other small-molecule therapeutic agents (3).The oceans cover more than 70% of the earth's surface, and little is known about the microbial diversity of marine sediments. As with terrestrial soils, marine sediments contain limited amounts of readily available organic matter, with most sources of carbon being present in complex forms (i.e., cellulose and chitin). However, culture-independent methods have demonstrated that marine sediments contain a wide range of unique microo...

Anti-methicillin Resistant Staphylococcus aureus Compound Isolation from Halophilic Bacillus amyloliquefaciens MHB1 and Determination of Its Mode of Action Using Electron Microscope and Flow Cytometry Analysis

“…Hence, many investigators have focused on marine sources for the isolation of unusual natural products with a unique chemical structure [8,9]. Moreover, from marine sources, many numbers of anti-MRSA metabolites have been isolated from different types of bacteria such as Pseudomonas fluorescens, Actinomycetes, Streptomyces, Marinispora and Bacillus species.…”

An assessment of actinobacterial diversity in the marine environment

“…Early support for the existence of indigenous marine actinomycete populations came from the recovery of strains from deep-sea sediments (Weyland 1969), the description of the first marine species (Helmke and Weyland 1984), and the isolation of seawater dependent strains (Jensen et al 1991). More recently, cultivation efforts have revealed considerable actinomycete diversity within marine samples (Gontang et al 2007;Jensen et al 2005;Magarvey et al 2004;Maldonado et al 2005b) and there is now evidence that actinomycetes are capable of growth in the marine environment Moran et al 1995). The recent description of three marine genera (Han et al 2003;Maldonado et al 2005a;Yi et al 2004) provides strong support for the concept of marine-specific actinomycetes, however some marine communities are dominated by taxa that have also been reported from land (Prieto-Davo et al accepted) leaving questions about the extent to which the communities in these two habitats differ.…”

Streptokordin, a New Cytotoxic Compound of the Methylpyridine Class from a Marine-derived Streptomyces sp. KORDI-3238

“…The oceans represent an under-explored environment for microbial diversity and novel secondary metabolites. Marine sediments, in particular, have been largely overlooked [7].…”