In Situ Raman Analysis of Biofilm Exopolysaccharides Formed in Streptococcus mutans and Streptococcus sanguinis Commensal Cultures.

This study probed in vitro the mechanisms of competition/coexistence between Streptococcus sanguinis (known for being correlated with health in the oral cavity) and Streptococcus mutans (responsible for aciduric oral environment and formation of caries) by means of quantitative Raman spectroscopy and imaging. In situ Raman assessments of live bacterial culture/coculture focusing on biofilm exopolysaccharides supported the hypothesis that both species engaged in antagonistic interactions. Experiments of simultaneous colonization always resulted in coexistence, but they also revealed fundamental alterations of the biofilm with respect to their water-insoluble glucan structure. Raman spectra (collected at fixed time but different bacterial ratios) showed clear changes in chemical bonds in glucans, which pointed to an action by Streptococcus sanguinis to discontinue the impermeability of the biofilm constructed by Streptococcus mutans. The concurrent effects of glycosidic bond cleavage in water-insoluble α - 1,3-glucan and oxidation at various sites in glucans' molecular chains supported the hypothesis that secretion of oxygen radicals was the main "chemical weapon" used by Streptococcus sanguinis in coculture.

In Vitro Enzymatic Polymerization of α-1,6-Graft-α-1,3-glucan and Structural Analysis of Gel Formation.

α-1,6-Graft-α-1,3-glucan comprises a main-chain of α-1,6-glucan and side-chains of α-1,3-glucan. It was synthesized by a one-pot in vitro enzymatic polymerization of sucrose and dextran (α-1,6-glucan) of different molecular weights. In the presence of the high-molecular-weightdextran (Mw ≥ 650 000), the graft glucan formed a self-standing hydrogel without any cross-linker. It was possible to control the number of α-1,3-glucan side-chains by controlling the molecular weight and concentration of the dextran. Consequently, it was possible to control the compression strength of the obtained gels. Hydrogels of the graft glucan were formed by physically cross-linking the α-1,3-glucan side-chains. These physical gels are potentially useful biomaterials with high biocompatible, because the graft glucan is composed of glucose alone.

High Tensile Strength Regenerated α-1,3-Glucan Fiber and Crystal Transition.

α-1,3-Glucan is a linear and crystalline polysaccharide which is synthesized by in vitro enzymatic polymerization from sucrose. A previous study reported that regenerated fibers of α-1,3-glucan were prepared using a wet-spinning method. However, the mechanical properties were poorer than cellulose regenerated fibers. Then, in this study, the mechanical properties of the regenerated α-1,3-glucan fiber were improved by the transformation of the crystal structure and stretching. The regenerated fiber stretched in water and dehydrated by heating showed high tensile strength (18 cN/tex) that is comparable with that of viscose rayon. Moreover, the crystal structures of the regenerated fibers were investigated using wide-angle X-ray diffraction (WAXD). To date, four crystal polymorphs of α-1,3-glucan from polymorph I to IV have been reported. This study revealed that the regenerated α-1,3-glucan fibers had two different polymorphs, polymorph II (hydrated form) and polymorph III (anhydrous form), depending on post-treatment methods of stretching and annealing procedures. Furthermore, the obtained distinctive 2D-WAXD patterns suggested that polymorph III is identical to polymorph IV.