The dextranase added in current commercial dextranase-containing mouthwashes is largely from fungi. However, fungal dextranase has shown much higher optimum temperature than bacterial dextranase and relatively low activity when used in human oral cavities. Bacterial dextranase has been considered to be more effective and suitable for dental caries prevention. In this study, a dextranase (Dex410) from marine Arthrobacter sp. was purified and characterized. Dex410 is a 64-kDa endoglycosidase. The specific activity of Dex410 was 11.9 U/mg at optimum pH 5.5 and 45 °C. The main end-product of Dex410 was isomaltotriose, isomaltoteraose, and isomaltopentaose by hydrolyzing dextran T2000. In vitro studies showed that Dex410 effectively inhibited the Streptococcus mutans biofilm growth in coverage, biomass, and water-soluble glucan (WSG) by more than 80, 90, and 95 %, respectively. The animal experiment revealed that for short-term use (1.5 months), both Dex410 and the commercial mouthwash Biotene (Laclede Professional Products, Gardena, CA, USA) had a significant inhibitory effect on caries (p = 0.0008 and 0.0001, respectively), while for long-term use (3 months), only Dex410 showed significant inhibitory effect on dental caries (p = 0.005). The dextranase Dex410 from a marine-derived Arthrobacter sp. strain possessed the enzyme properties suitable to human oral environment and applicable to oral hygiene products.
The gene encoding a new extracellular amylopullulanase (type II pullulanase) was cloned from an extremely thermophilic anaerobic archaeon Thermococcus siculi strain HJ21 isolated previously from a deep-sea hydrothermal vent. The functional hydrolytic domain of the amylopullulanase (TsiApuN) and its MalE fusion protein (MTsiApuN) were expressed heterologously. The complete amylopullulanase (TsiApu) was also purified from fermentation broth of the strain. The pullulanase and amylase activities of the three enzymes were characterized. TsiApu had optimum temperature of 95°C for the both activities, while MTsiApuN and TsiApuN had a higher optimum temperature of 100°C. The residual total activities of MTsiApuN and TsiApuN were both 89% after incubation at 100°C for 1 h, while that of TsiApu was 70%. For all the three enzymes the optimum pHs for amylase and pullulanase activities were 5.0 and 6.0, respectively. By analyzing enzymatic properties of the three enzymes, this study suggests that the carboxy terminal region of TsiApu might interfere with the thermoactivity. The acidic thermoactive amylopullulanases MTsiApuN and TsiApuN could be further employed for industrial saccharification of starch.
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