الفهرس 
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Abstract
The present study focused on discovering and producing new marine biopolymers of interest in pharmaceutical and industrial applications, so, it was important to find a new marine producer from a new habitat. The effect of solar energy in addition to wind on the small ponds formed from the water percolating from Suez Canal in El-kantara Gharb region made it ideal location for isolation of such organisms. The isolation and screening steps gave two isolates had the ability to produce a considerable amount of polysaccharide.
The two isolates were more close to chromohalobacter salexigens DSM 3043 with the maximum identity of 99% and 97% for isolates HW1 and HW5 respectively. Sequence data were submited to GenBank. And it provided a GenBank accession numbers for nucleotide sequences as follow HW1= chromohalobacter salexigens KT989776, HW5= chromohalobacter salexigens KT989777.
To confirm the difference between the two strains, antibiotic sensitivity test was proceeded and proved that the two strains were different.
To optimize the production of polysaccharide from the two strains, a series of experiments were proceeded as follow:-
Initial pH (6-10), where the optimum pH for chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 was 8 and the maximum polymer production was 2.4, 2.7 mg/ml respectively.
The optimum temperature for polymer production by both chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 was 25C and the maximum polymer production was 2.4, 2.8 mg/ml respectively.
The optimum sodium chloride concentration for polymer production by both chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 was 15% and the maximum yield was 2.56, 3.57 mg/ml respectively.
Sucrose was the best carbon source for the production of polymer from chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 and the maximum polymer production was 2.88, 3.7 mg/ml, respectively. While the maximum biomass yield was observed when mannitol was used. the optimum sucrose concentration for chromohalobacter salexigens KT989776 was 5% and for chromohalobacter salexigens KT989777 was 3% , the maximum polymer production was 3.39, 4.68 mg/ml respectively.
Ammonium sulphate was the best nitrogen source for chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 and the maximum polymer production was 3.3, 4.1 mg/ml respectively. On the other hand, optimum ammonium sulphate concentration for chromohalobacter salexigens KT989776 was 0.153 % and for chromohalobacter salexigens KT989777 was 0.08% , the maximum polymer production was 3.76, 4.91 mg/ml respectively.
Potassium di-hydrogen phosphate was the best phosphorous source for chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 with the maximum polymer production 5.7, 5.5 mg/ml respectively. While its optimum concentration for the production of polymer from chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 was 0.5 g/l, the maximum polymer production was 6.1, 5.8 mg/ml respectively.
A sharp increase in polymer production by the two strains was recorded when the culture was incubated at optimum temperature for growth for 48 h followed by storing at 4C for 24 h in case of chromohalobacter salexigens KT989776 where the polymer production reached 11.9 mg/ml and in case of chromohalobacter salexigens KT989777, incubation for 24 h at optimum temperature followed by incubation at 4 C was the optimum for polymer production (10.2 mg/ml)
The resulting polymer was purified and its chemical structure was elucidated using paper chromatography, FT-IR and NMR spectroscopy, the results proved that the resulting polymer is a homo polysaccharide polymer (levan)
In order to decrease the cost of levan production by C. salexigens , molasses were used instead of sucrose and the result was promising where the production reached 10.1, 9.3 mg/ml for chromohalobacter salexigens KT989776 and chromohalobacter salexigens KT989777 respectively when grew in treated sugar beet molasses.
The ability of the two strains to form biofilm in microplate was studied and the results showed that chromohalobacter salexigens KT989776 has higher ability to form biofilm than chromohalobacter salexigens KT989777.
In order to enlarge the biological activity spectrum of resulted levan, two chemical modifications (carboxymethylation and sulphation) were done and the biological activity of each derivative was determined. The sulphated levan gave higher results as anti-tumor agent than other two derivatives. Also it was proved in this study that sulphated levan of the two strains possess fibrinolytic activity higher than the commercial product heamoclar.
In another application, the use of levan as a prebiotic agent was determined and it was proved that our product can be consumed as prebiotic agent by lactobacillus sp.