الملخص الإنجليزي
Marine biofouling communities are composed of diverse species of micro- and macro- fouling organisms. Actinomycetes comprised about 10% of the marine bacterial fouling community. Species belonging to the genus Streptomyces are well-known producers of bioactive natural products with high potential for biotechnology. In this project, the bacterial biofouling communities developed on acrylic panels deployed at different depths (3, 6 and 15 m) and at different distances from the coastline (0.5 and 1.5 km) were characterized using next generation MiSeq sequencing of 16S rRNA genes. These biofilms were used for the isolation of microorganisms, targeting specifically those belonging to Actinomycetes. The obtained strains were identified by 16S rRNA sequencing and then screened for the production of antibacterial, antifungal, antioxidants, and enzyme inhibitory compounds. Pure compounds were isolated from the strain that showed the highest bioactivity and the chemical structure of these compounds was elucidated using nuclear magnetic resonance (NMR) techniques, highresolution electron spray ionization mass spectrometry (HR-ESI-MS) and comparison with the literature data. MiSeq sequencing data revealed a clear shift in the bacterial fouling community structure, depending on both depth and distance from the coastline. The total biomass, bacterial counts and chlorophyll a of the biofilms decreased with increasing depth at both locations. Five Streptomyces strains were isolated from these biofouling communities and were molecularly identified as Streptomyces eurythermus sp.76, Streptomyces sampsonii sp.80, Streptomyces nodosus sp.81, Streptomyces andamanensis sp.83 and Streptomyces tendae sp. 89. These strains were able to produce the extracellular enzymes cellulase, phosphatase and glucosidase and their chemical extracts showed variable antibacterial, antifungal, antioxidant and enzymes inhibition activities. In our continued interest in isolation of secondary • metabolites from natural sources, three pure compounds 1-3 were isolated from the marine
strain Streptomyces nodosus. Compounds (1) 2, 4-dimethyl-docasonoic acid and (2) cyclo (Lleu-L-pro) were isolated from the marine Streptomyces nodosus strain for the first time, while compound (3) cyclo (L-leu-(N-ethenthiol)-L-pro) was isolated as new natural product. The local marine environment could provide a valuable platform for the discovery of new biologically active secondary metabolites and the search for more novel and useful compounds should not stop.
