الفهرس 
Introduction
Summary and conclusionsOnly 14 pages are availabe for public view
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Abstract
The antibiotic resistant pathogens cause a serious problem for physicians because their infections become difficult to be controlled. Moreover, the rise in the number of resistant microorganisms and the development of multi-drug resistant ones, which can escape the actions of all known antibiotics, make the situation more complicated. Unfortunately, while we are suffering from such resistant to the known antibiotics the number of newly discovered ones decreases; only three novel antibiotics were discovered during the last ten years. from such facts it can be concluded that we are in an urgent need for novel antibiotics with new modes of actions to overcome that crisis.
The microorganisms notably the actinomycetes are rich source of natural products especially the antibiotics. Since 2000, eight out of the eleven naturally produced antibiotics were derived from the actinomycetes. Among the actinomycetes, the Streptomyces is considered the richest source of the active metabolites as they produced 80% of the active metabolites derived from the actinomycetes. Also others non-Streptomyces actinomycetes were proved to have good capabilities as exemplified by Saccharomonospora and Nocardiopsis genera. The whole genome sequence study of the Saccharomonospora azurea SZMC 14600 showed that it is an excellent model for discovering new metabolites, and also new antibiotics were discovered from Nocardiopsis species. Interestingly, screening novel isolates following new techniques raises the probability in obtaining new antibiotics. Such novel species can be isolated from the neglected habitats using selective methods to avoid the re-isolation of previously known species. So, the hope is renewed in exploring the neglected habitats notably the marine one looking for novel actinomycetes which expected to have good potentialities.
The mangrove forests are neglected marine habitat located in tropical and subtropical regions. Interestingly, new antibiotics were discovered from novel actinomycetes isolated from the mangrove habitat in India and China. In this project, the mangrove forests along the Red Sea coast, Egypt were screened for novel actinomycetes which might produce novel antibiotics.
Soil samples were collected from three mangrove forests along the Red Sea coast, Egypt. The isolation was carried out using a heat pre-treatment regime as a selective isolation method on two media SM3 and M1 supplemented with sea salt (3.3%, w/v). Seventeen actinomycetes isolates were chosen from the plates according to their colonial morphology and pigmentation pattern, purified and maintained on slopes and in glycerol cultures.
The ability of the isolates to control the growth of pathogenic microorganisms was tested using disc diffusion method and the isolates were screened against Bacillus subtilis, Escherichia coli, Mycobacterium phlei, Pseudomonas aeruginosa, Salmonella typhi, Sarcina luteaand, Staphylococcus aureus and Candida albicans,. from the seventeen isolates, four were active against Bacillus subtilis, two against Candida albicans, ten against Escherichia coli, four against Mycobacterium phlei, three against Pseudomonas aeruginosa, twelve against Sarcina luteaand and five aganist Staphylococcus aureu
The 16S rRNA gene sequence analysis was performed and the isolates were assigned to the following genus: Nocardiopsis (six isolates), Saccharomonospora (two isolates) and Streptomyces (nine isolates). Such results also were supported by the chemotaxonomic and morphological data. The 16S rRNA gene trees were generated using MEGA version 4 software testing three different algorithms. According to the resultant trees, Streptomyces strains 1, 3, 21 and 23 formed distinct phyletic lines with heterogeneous clades in the Streptomyces 16S rRNA gene tree, sharing a low 16S rRNA gene sequence similarity value with their nearest taxonomic neighbour ranging from 97-98.8%. Also Saccharomonospora isolate 8 and Nocardiopsis isolates 11, 13, 17 and 24 formed distinct phyletic lines within Saccharomonospora and Nocardiopsis 16S rRNA gene trees, respectively.
The Streptomyces and Saccharomonospora isolates were screened for phenotypic characters known to be of a value in the actinomycetes systematic. The phenotypic tests were performed to examine the ability of the isolates to degrade different insoluble compounds; hydrolyze the arbutin and easculin; reduce the nitrate and nitrite; produce hydrogen sulphide; grow at different pH, temperature and NaCl concentrations; require sea salt for growth; utilize different carbon sources (a sole carbon source, organic and inorganic) for energy. Interestingly, three of the Streptomyces isolates 1, 21 and 23 were recorded to be obligate marine actinomycetes; cannot grow without the sea salt.
The taxonomic position of Streptomyces isolate 1 was studied extensively as the isolate formed a distinct phyletic line within the Streptomyces radiopugnans 16S rRNA gene clade, a result which was supported by all the tree making algorithms and 94% bootstrap value. The isolate shared 98.7% 16S rRNA gene sequence similarity value with its closest related phylogenetic neighbour namely, Streptomyces fenghuangensis. Also the isolate 1 can be easily distinguished from all the clade members using a range of the phenotypic properties. According to the obtained genetic and phonetic data, isolate 1 can be proposed as a novel Streptomyces species.
Interestingly, the Saccharomonospora isolate 8 can be considered as a putative novel species. It shared 98.7% 16S rRNA gene similarity with its closest taxonomic neighbour Saccharomonospora cyanea NA134T. However, more comparative taxonomic studies still required to distinguish both isolates and confirming that they are different.
It can be concluded that the marine habitats notably the mangrove forests form a reproductive unexploited source for the novel actinomycetes strains which have high capabilities to produce potentially active secondary metabolites.