الفهرس 
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Abstract
Screening of five different isolates from different sources of honey bees was carried out for production of dextranase enzyme using dextranase production medium (Medium I).
2- Primary identification of the most potent isolate which has the ability to give the highest dextranase activity (258 U/ml) was carried out
using16S rRNA analysis and identification by 16-23S intergenic region as Bacillus subtilis NRC-B233.
3- Different types of wastes and cheap materials were tested for the dextranase production. Corn flour was selected as the best substrate for
the production of dextranase as it gave the maximum dextranase activity.
4- Solid state fermentation (SSF) was achieved under static condition for the production of dextranase to save energy. The optimum
incubation period was after 32 hours as it gave maximum dextranase activity and specific enzyme activity (158.961 U/g and 4.018 U/mg , respectively).
5- The highest yield of dextranase was at temperature 37 oC.
6- The dextranase activity was influenced by the moisture content. The potent activity was noticed at 20 ml where it gave the highest dextranase and specific enzyme activities (170.624 U/g and 5.183 U/mg, respectively).
7- The dextranase activity was influenced by different initial pHs [ acidic pH (3-6) , neutral pH (7) and alkaline pH (9-11)]. The optimum one was pH (10), it gave the highest dextranase activity (216.134 U/g) and specific enzyme activity (7.397 U/mg).
8- Some salts were individually added to the production medium.
CrCl3 (0.1M) was the best salt which increased the dextranase and specific enzyme activities (447.580 U/g and 14.200 U/mg, respectively). The best concentration of CrCl3 was (0.175 M)
where dextranase activity and specific enzyme activity increased (795.161 U/g and 20.2020U/mg , respectively).
9- Different nitrogen sources were added individually to the production medium. Peptone (2g/l) increased the dextranase activity up to
( 1255.031 U/g) and specific enzyme activity (36.943 U/mg).
10- Different carbon sources were tested. It was noticed that starch (10g/l) gave the maximum dextranase activity (1553.364 U/g) and specific enzyme activity (42.769 U/g).
11- Improvement in dextranase enzyme activity was achieved by simple UV mutation for Bacillus subtilis NRC-B233 which increased the enzyme activity and specific enzyme activity up to (2842.294 U/g and 53.480 U/mg , respectively) after the exposure of the wild type strain to UV lamp for 15 min. The repeated batch test showed that the mutant was stable for 10 cycles without reduction in activity.
12- The crude enzyme was highly tolerant to repeated freezing and thawing , the activity remaining at 100% for three months.
13- Partial purification of the crude dextranase produced by Bacillus subtilis NRC-B233 was carried out by ultrafiltration then fractional
precipitation by acetone and ethanol. The use of ultrafiltration for downstream processing would result in one-step, cost-effective method for dextranase recovery. The molecular weight of the partially purified enzyme was less than 10 KDa. The fraction 70% acetone showed the highest specific enzyme activity and purification fold
(6261 U/mg and 112.2 fold , respectively).
14- Studying the properties of partially purified dextranase enzyme was carried out. The optimum pH value was 9.2 .The optimum temperature was at 70 oC. The enzyme retained full activity (100%) at 75 oC for one hour so it was thermostable. The pH of the dextranase enzyme exhibited stability at pH directed to acidity or alkalinity.
15- The partially purified dextranase was greatly affected by the metal ions addition. The halophilic feature of this enzyme appeared clearly when the enzyme activity increased about 4 fold in the presence of 10% NaCl. The maximum dextranase activity was showed in case of using CaCl2 (0.050M) , EDTA (0.100M) & KCl (0.150M).
16- The calculated values of Km and Vmax using different concentrations of dextran (150.000 M.wt) as a substrate were found to be (4.46 and 41.66 mg/ml , respectively).
17- Studying the effect of partially purified dextranase on stored high viscous sugar cane juice showed high reduction .The decrease in viscosity due to dextranase action.
18- The enzyme showed variable degradation effect on different types of dextran and carbohydrates of α-1,4 and α-1,6 glycosidic linkages.
Blue dextran (1000 M.wt) gave the maximum enzyme activity (273.8 %) followed by the starch and amylopectin (α-1,6 glycosidic linkage) (228% and 165% , respectively).
We can summarize that Bacillus subtilis NRC-B233 dextranase is industrially important from the perspectives of its activity at abroad pH
range (5.0-10.0). In addition, thermostability, halophilic characteristics and ability to degrade different types of α-1,4 and α-1,6 glycosidic
linkages. This representive more attractive characteristics for application of this enzyme in industrial scale.
In this study we focused on isolation of halophilic bacteria from honey Bacillus subtilis NRC-B233 as new source for dextranase production.
The mutagenic honey isolate produced a novel halophilic low molecular
weight constitutive dextranase characterized by unique features, like thermostability and pH stability.
Further, cheap medium like corn flour would be a superior alternative to the already available expensive dextran, since 30-40 % of the
production cost of industrial enzymes is accounted by the cost of the growth medium.