الفهرس 
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Abstract
The field of natural active metabolites attracts the attention of many investigators all over the world, thus, the present study aims at isolation of bioactive metabolite(s) from marine thermotolerant actinomycete strains and evaluating their activities as thermostable antibiotics, with subsequent bioactivity-guided fractionation of the most prominent species, to finally isolate and identify chemical compound with promising biological activity.
Actinomycetes are considered as one of the main sources for production of several natural active metabolites such as antibiotics, anticancers, antiviral and enzyme inhibitors, etc. also the synthetic active compounds have side effect as well as, the appearance of resistance strains on long term that leas to the essentiality of discovering new active natural metabolites. One of the main roles for discovering new natural active compounds is looking for new sources for isolation.
Isolation of actinomycete cultures from different habitats.
This study began with isolation of seventy five actinomycete isolates from Salwa beach located in Jazan region, Kingdom of Saudi Arabia (KSA). Salwa beach covered with green areas of mangrove trees.
Screening for thermophilic isolates among the obtained actinomycetes.
The eventy five actinomycete isolates that obtained from the previous step were screened for their ability to grow at different high temperature degrees above isolation temperature 45˚C to select thermophilic types.
Among screened isolates; only fifteen were succeed to grow at a temperature degree above 50˚C while, sixty isolates failed to grow at the same temperature degrees. The growth of the fifteen isolates was ranged from 50-65˚C.
Screening for antimicrobial activities of the obtained thermophilic actinomycetes.
Among the fifteen thermophilic actinomycete isolates which were tested for their ability to produce antimicrobial activities, only all isolates exhibited various degrees of activities against the tested microorganisms by cultivation on the growth medium.
The most potent actinomycete isolate SJ11 exhibited the highest antimicrobial activities against the tested microorganisms, the isolate SJ11 was selected for further studies concerning its identification.
Phylogenetic analysis of 16S rRNA gene; in addition to biochemical studies and culture characteristics which described by the International Streptomyces project as well as the chemical analyses of the cell wall, were carried out for the isolate under study.
On the basis of the accumulated characteristics of the most active actinomycete isolates under study and consulting the recommended International Key’s of Bergey’s Manual for identification of actinomycetes (1974, 1989 & 1994), it was found that the actinomycete isolate SJ11, was found to be more similar to Saccharomonospora sp.
Production and extraction of the extracellular bioactive compound by Saccharomonospora sp, SJ11.
The most potent actinomycete isolate which was identified as Saccharomonospora sp, SJ11 was selected for the biosynthesis of the active metabolite. For this reason this isolate was inoculated in nutrient broth media under favorable environmental and nutritional conditions.
At the end of the incubation period, the fermentation broth was harvested (25.0 liters) and filtered through cotton wool then; the clear filtrate was exposed to the extraction process. Then active metabolite was extracted by mixture of chloroform : methanol in the ratio (2:1 v/v) at pH 7.0. The organic phase was collected and evaporated under reduced pressure using a rotary evaporator. The extract was concentrated as reddish black viscous syrup and treated with petroleum ether (b.p. 60-80°C) for precipitation process.
Preparation and biological testing of the fractions.
Silica gel column chromatography was adopted for the bioactivity-guided fractionation of the crude extract, using increasing proportions of ethyl acetate in hexane as eluent. All the fractions obtained were individually tested for their antimicrobial activity against Bacillus subtilus ATCC 6633. It was found that one fraction was active against the tested bacterial strain.
Isolation and identification of the isolated compound S–11.
Bioactivity-guided fractionation of Saccharomonospora sp SJ11 fractions led to the isolation of one compound. The active compound under study was tested for its physical and chemical characteristics.
Structure elucidation and identification of the pure isolated compound was carried out through spectral analysis comprising UV, IR, EIMS and 1H-NMR methods, and comparing the obtained data with that available in the current literature and by consulting the recommended identification keys of antibiotics such as: umezawa (1977) it could be stated that, the produced active compound is belonging to anthracyclines group and identified as a derivative of daunomycin. This compound is orange in acidic violet in alkaline, molecular weight: 372 dalton and molecular formula: C23H16O5 and it was gave the name SJ11.