الفهرس 
LIST OF ABBREVIATIONSOnly 14 pages are availabe for public view
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Abstract
With increasing environmental awareness and emphasis on a sustainable society in harmony with the global environment, biosurfactants have been becoming much more important. Biosurfactants are amphiphilic compounds, produced by living organisms mostly as secondary metabolites and reduce the interfacial tension as well as the surface tension (1). Biosurfactants have several advantages over the chemical surfactants including low toxicity, good biodegradability, effectiveness at extreme temperatures or pH values and ecological acceptability (4-6). In addition, biosurfactants have been classified according to their structure into glycolipids, lipopeptides, mycolates, polymeric, particulate, phospholipids, fatty acids, and neutral lipids (3).
Owing to the diversity and the environmentally friendly nature of biosurfactants as well as their suitability for large-scale production and selectivity, biosurfactants became important biotechnology products for industrial, agricultural and medical applications (2). For medical applications, biosurfactants are useful as antimicrobial agent (113-138). Some biosurfactants have also been found to have anti-adhesive and anti-biofilm activity which is useful in both food and pharmaceutical industries (140-150, 164, 349).
Due to the excellent self-organizing properties of some biosurfactants, it was found that many biosurfactants may be a new functional material in nanobiotechnology and in drug delivery system (354-356). In 2006 and up to present, many literatures reported that biosurfactants were involved in the synthesis and stabilization of silver nanoparticles (358-364). Recently, it was found that biosurfactants have many applications in cosmetics and in skin care products for skin roughness improvement as natural ceramides (365).
Consequently, screening for potent biosurfactants-producing microorganisms in Egypt, the optimization for large scale production of biosurfactants and studying of some of its possible pharmaceutical applications were the main goals of this study.
Seventy nine strains were collected from different accessible sources including; standard strains ATCC, NCTC, DSMZ, different clinical specimens and from diverse environmental samples. They were screened for their biosurfactants-producing capability using oil spreading technique (OIL) and the emulsification index (EI 24) (96, 105). Out of all tested microbial strains, only 12 were able to produce biosurfactants including one standard strains, 4 clinical isolates and 7 from environmental samples.
After microscopical and biochemical characterization, the eleven biosurfactants-producing microorganisms were identified to be 9 Pseudomonas strains, four of them clinical isolates, one Klebsiella (environmental strain 5) and one Gram positive strain suspected to be Bacillus sp. (environmental strain B4).
The most potent biosurfactants-producing strain was found to be the clinical P. aeruginosa isolate P103 since it showed the maximum oil spreading, 140 mm. On the other hand, Pseudomonas isolate 6 was the most potent biosurfactants-producing strains isolated from environmental sample. In addition, Bacillus isolate B4 was the only Gram positive isolate producing biosurfactants.
After molecular characterization of isolates P 103 and B4, phylogenetic trees were constructed and they were found to be P. aeruginosa strain and B. subtilis, which close matches to B. subtilis subsp. subtilis strain CICC 10260. They were also physiologically characterized by studying their susceptibilities to different antibiotics and their growth patterns.