**Wei Ren 1,2,3, Ruanhong Cai 2,4, Wanli Yan 1,3,5, Mingsheng Lyu 1,3,5, Yaowei Fang 1,3,5 and Shujun Wang 1,3,5,\***


Received: 18 November 2017; Accepted: 31 January 2018; Published: 7 February 2018

**Abstract:** This study evaluated the ability of a dextranase from a marine bacterium *Catenovulum* sp. (Cadex) to impede formation of *Streptococcus mutans* biofilms, a primary pathogen of dental caries, one of the most common human infectious diseases. Cadex was purified 29.6-fold and had a specific activity of 2309 U/mg protein and molecular weight of 75 kDa. Cadex showed maximum activity at pH 8.0 and 40 ◦C and was stable at temperatures under 30 ◦C and at pH ranging from 5.0 to 11.0. A metal ion and chemical dependency study showed that Mn2+ and Sr2+ exerted positive effects on Cadex, whereas Cu2+, Fe3+, Zn2+, Cd2+, Ni2+, and Co2+ functioned as inhibitors. Several teeth rinsing product reagents, including carboxybenzene, ethanol, sodium fluoride, and xylitol were found to have no effects on Cadex activity. A substrate specificity study showed that Cadex specifically cleaved the α-1,6 glycosidic bond. Thin layer chromatogram and high-performance liquid chromatography indicated that the main hydrolysis products were isomaltoogligosaccharides. Crystal violet staining and scanning electron microscopy showed that Cadex impeded the formation of *S. mutans* biofilm to some extent. In conclusion, Cadex from a marine bacterium was shown to be an alkaline and cold-adapted endo-type dextranase suitable for development of a novel marine agent for the treatment of dental caries.

**Keywords:** marine agent; *Catenovulum*; alkaline and cold-adapted dextranase; isomaltoogligosaccharides; biofilm; dental caries
