Identification and comparison of two closely related dextransucrases released by water kefir borne Lactobacillus hordei TMW 1.1822 and Lactobacillus nagelii TMW 1.1827

• Published in: Microbiology (Society for General Microbiology) Vol. 165; no. 9; pp. 956 - 966
• Main Authors: Bechtner, Julia, Wefers, Daniel, Schmid, Jonas, Vogel, Rudi F, Jakob, Frank
• Format: Journal Article
• Language: English
• Published: England 01.09.2019
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Fermentation; Glucosyltransferases - chemistry; Glucosyltransferases - metabolism; Kefir - microbiology; Lactobacillus - enzymology; Lactobacillus - isolation & purification; Sucrose - metabolism; Dextransucrase; Lactobacillus hordei; Lactobacillus nagelii; Native Enzymes; Water kefir
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.000825

Dextransucrases are extracellular enzymes, which are exclusively expressed by lactic acid bacteria (LAB) and produce α-1→6 linked glucose polymers from sucrose. In this study, two dextransucrases derived from water kefir borne TMW 1.1822 and TMW 1.1827 were identified and comparatively investigated. Differences between both proteins mainly arise from an additional C-terminal glucan-binding domain and the presence of a signal motif in the TMW 1.1827 dextransucrase. TMW 1.1822 released the enzyme only in the presence of its substrate sucrose in contrast to TMW 1.1827, while both strains functionally expressed the dextransucrases independently of sucrose. Both enzymes could be recovered as crude protein extracts in culture supernatants, as they are not covalently bound to the cell surface. This enabled the formation of dextrans at equal reaction conditions as well as their subsequent structural analysis in terms of molecular structure and molecular weight. The volumetric transglycosylation and hydrolysis activities were distinctly different for both enzymes, which produced -branched dextrans with a comparable degree of branching. Moreover, identical oligosaccharides were obtained for both dextrans upon -dextranase digestion, while some differences in the polysaccharide fine structures could be identified from the varying portions of certain oligosaccharides. Dextrans synthesized by the dextransucrase released by exhibited an averaged molecular weight ( ) of 7.9×10 Da, while those produced by the dextransucrase released by exhibited an of 6.1×10 Da. Moreover, glycosylation of glucansucrases by LAB was identified for the first time for the released dextransucrase of TMW 1.1827. Our study therefore reveals new molecular insights into how dextransucrases released by water kefir borne TMW 1.1822 and TMW 1.1827 contribute to the complex formation of the traditional beverage water kefir.