الفهرس 
1. INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Over many years, natural products have been always playing animportant role in the search for novel drugs or drug candidates.Natural products are an inspiring source for researchers due to their structural complexity and diversity. Today, more than fifty percent of the drugs prescribed are natural products or semisynthetic derivatives (Schneider et al., 2008).
The most pre-eminentorganisms producing natural products were found to bewithin three groups of organisms: plants, bacteria (actinomycetes, myxobacteria and cyanobacteria) and fungi. Although plants and plant extracts have been playing a remarkable role in traditional medicine for manyyears; the discovery of microbial natural products had only been made great development of natural sciences during the twentieth century (Koehn and Carter, 2005).
Especially since the discovery of penicillin in 1929, metabolites of microbial origin are known for valuable supply of compounds with new structures in the need for drug candidates against infectious diseases (Newman and Cragg, 2007).
In addition to numerous antibacterial agents have been developed and marketed for clinical use and have ameliorated the massive human mortalities previously associated with bacterial infections before the ‘‘antibiotic era.’’(Livermore, 2003).However, the initial optimism that all bacterial infections could be successfully treated with these new agents was quickly disabused when reports of resistance emerged soon after their introduction into clinical use(Furuya, 2006).
Microbial secondary metabolites of low molecular weight productsinclude antibiotics, toxins, enzyme inhibitors, pigments, pesticides, effectors of ecological competition and symbiotic relation, immuno-modulating agents, receptor antagonists and agonists, pheromones, antitumor agents and growth promoters for higher living organisms. These microbial secondary metabolites exhibited major effects on animals and plants health, nutrition and economics (Demain, 1992).
Antibiotics provide the main basis for the therapy of microbial infections. Since the discovery of these antibiotics and their uses as chemotherapeutic agents, there was a belief in the medical fraternity that this would lead to the eventual eradication of infectious diseases. However, overuse of antibiotics has become the major factor for the emergence and dissemination of multi-drug resistant (MDR) strains of several groups of microorganisms (Harbottle et al., 2006).
Several pathogenic bacteriacontinuethe development of antibiotic resistance emergence and the increase in numbers of new pathogensthat are themain causeof interest in discovering new biologically active compounds for drug discovery. It is critical that new groups of microbes from unexplored habitats be pursued as sources of new drugs or therapeutic agents (Bull et al., 2005).
Actinobacteria, as prokaryotic organisms, have made anefficient contribution to the human health through the world (Demain and Sanchez, 2009). Novel genera in Actinobacteria need to be examined in the search for bioactive metabolites with differentbiological activities (Baltz, 2006). The isolation frequency of actinomyc.