Characterization of Extracellular Dextranase from a Novel HalophilicBacillus subtilis NRC-B233ba Mutagenic Honey Isolate under Solid State Fermentation

Mona A. Esawy,Sara H. Mansour,Naziha M. Hassanein,Eman F. Ahmed,Hesham A. El Enshasy

doi:10.1155/2012/860619

Abstract

Bacillus subtilis NRC-B233bwas isolated from Libyan honey sample proved to be a potent dextranase producer by applying solid state fermentation and utilizing corn flour as the sole carbon source. The optimized culture conditions for dextranase productions were 37°C, pH 10, 32 h, and 20% (v/w) moisture content. A unique character of this isolate is its ability to produce steady dextranase irrespective to the presence of NaCl in the medium. The addition of 0.175 Mm CrCl3 increased the enzyme production by about 4.5 fold. Further improvement in enzyme production was achieved by simple UV mutation which increased the enzyme production up to about 2842 U/g. The crude extract has been partially purified about 112-fold from crude extract by only two purification steps involving ultra-filtration. The partially purified dextranase showed its maximum activity at pH 9.2 and 70°C. It retained full activity (100%) at 75°C for one hour. Dextranase activity increased about 4 fold in the presence of 10% NaCl. This enzyme showed variable degradation effect on different types of dextran and its derivatives. The treatment of viscous sugar cane juice with the enzyme preparation resulted in clear visual dextran hydrolysis. These results suggest that the dextranase produced byBacillus subtilis NRC-B233bis industrially applicable.

Highlights

Honey can be considered as a reservoir for microbes that withstand the concentrated sugar, acidity
The culture grew well when the medium was supplemented with different concentrations of (NaCl 0-12%) but it did not grow at higher NaCl concentration (15% NaCl) and the maximum growth was observed at 4% NaCl
The 16S rRNA gene sequence analysis indicated that the isolate was Bacillus sp. with 98% identity to any of these three species Bacillus spp., or B. licheniformis, or B. subtilis and they clustered into a monophyletic line in a phylogenetic tree

Summary

Introduction

Honey can be considered as a reservoir for microbes that withstand the concentrated sugar, acidity. These microbes contribute to the antimicrobial characters of honey. The osmophilic feature of the honey could hypothesize the presence of moderate halophilic bacteria with new properties. A considerable attention has been given to the enzymes produced by moderately halophilic microorganisms and their biotechnological potentials [1, 2]. In spite of the fact that many moderately and extremely halophilic microorganisms have been well described, the apparent thermostable properties of their enzymes, especially from moderately halophilic bacteria, have not studied extensively [6]

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