Production of a Novel Halophilic Dextranase from a Honey Isolate, Bacillus subtilis NRC-B233 under Solid-state Fermentation

A GRAM-POSITIVE, sporulating halophilic bacteria, designated NRC-B233, was isolated from the honey produced in Saudi Arabia. It was identified by the 16-23S intergenic region as Bacillus subtilis NRC-B233. Screening of the wastes and agro-products for dextranase production under solid state fermentation showed that corn flour was the best substrate (61.323 U/g). The optimum conditions for dextranase productions were 37°C, pH 9, 32 hr incubation period, and 200 % moisture content. The most favorable nitrogen and carbon sources for enzyme production were 2% peptone and 5% starch (1076.768, 1553.364 U/g). respectively. A unique character of this isolate is its ability to continuously produce dextranase in the absence and presence of NaCl 5-20 g/l. The addition of 0.175 Mm CrCl3 increased the dextranase production about 4.5 fold. The enzyme has been partially purified about 112-fold from crude extract by only two purification steps involving ultra-filtration. The purified dextranase showed its maximum activity at pH 9.2 and 70ºC. It retained full activity (100%) at 75ºC for one hour. Dextranase activity increased about four-fold in the presence of 10% NaCl. On the other hand, CaCl2 (0.050M), EDTA (0.100M), and KCl (0.100M) had great influence in enzyme activity. The enzyme showed variable degradation effects on different types of dextran and its derivatives.
These results suggest that the dextranase secreted by Bacillus subtilis NRC-B233 is industrially important from the perspectives of its activity at across pH range (5.0–10.0), its thermo-activity in addition to its halophilic character and its ability to degrade different types of α -1,4 and α-1,6 glycosidic linkages.