| Summary: | A GH49 dextranase gene DexKQ was cloned from marine bacteria <i>Arthrobacter oxydans</i> KQ11. It was recombinantly expressed using an <i>Escherichia coli</i> system. Recombinant DexKQ dextranase of 66 kDa exhibited the highest catalytic activity at pH 9.0 and 55 °C. kcat/Km of recombinant DexKQ at the optimum condition reached 3.03 s<sup>−1</sup> μM<sup>−1</sup>, which was six times that of commercial dextranase (0.5 s<sup>−1</sup> μM<sup>−1</sup>). DexKQ possessed a <i>K</i>m value of 67.99 µM against dextran T70 substrate with 70 kDa molecular weight. Thin-layer chromatography (TLC) analysis showed that main hydrolysis end products were isomalto-oligosaccharide (IMO) including isomaltotetraose, isomaltopantose, and isomaltohexaose. When compared with glucose, IMO could significantly improve growth of <i>Bifidobacterium longum</i> and <i>Lactobacillus rhamnosus</i> and inhibit growth of <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. This is the first report of dextranase from marine bacteria concerning recombinant expression and application in isomalto-oligosaccharide preparation.
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