The supernatant and pellet samples were kept at −25 °C until further use. Enzymatic activity was assayed in triplicate using the dinitrosalicylic acid (DNS) method (Sumner & Howell, 1935). One unit of dextransucrase activity is defined as the amount of enzyme that catalyzes the formation of 1 μmol fructose min−1 at 30 °C in 20 mM sodium acetate buffer (pH 5.4) with 292 mM sucrose. Supernatant and cell-associated fractions find more from Weissella cultures were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Each sample (30 μL) was mixed with NuPAGE® LDS sample buffer 4 × (10 μL) (Invitrogen, France) and incubated at 70 °C for 10 min to denature the

enzymes reversibly. Electrophoresis was performed on NuPAGE® 3–8% Tris-acetate gel with Selleckchem Ixazomib the XCell Surelock Minicell system (Invitrogen) at room temperature at constant voltage (150 V). After migration, proteins were stained with the Colloidal Blue Staining kit (Invitrogen). For in situ detection of dextransucrase activity, the gel was first washed three times with

sodium acetate buffer (20 mM sodium acetate, pH 5.4, 0.05 g L−1 CaCl2 and 0.1% v/v Triton X-100) for a total of 60 min to renaturate dextransucrase. It was then incubated overnight in the same buffer supplemented with sucrose (10% w/v). Thereafter, dextransucrase activity was revealed by periodic acid-Schiff staining (Schiff’s reagent, Sigma-Aldrich) of the polymer formed (Miller & Robyt, 1986). The molecular mass was estimated with the Precision Plus Protein Standards all blue purchased from BioRad Laboratories. The supernatant of W. cibaria K39 harvested from the glucose medium culture was concentrated up to fivefold with a Centricon (30 kDa cut-off, Millipore)

to reach a protein concentration around 1 g L−1, as determined by the Bradford method (Bradford, 1976), and subjected to SDS-PAGE. The proteins were stained with colloidal blue Coomassie and silver staining (ProteoSilver Plus Silver Stain kit, Sigma-Aldrich), which is more sensitive. however In addition, zymogram was performed to specifically detect dextransucrase activity. The unique band detected at 180 kDa was excised from the Coomassie blue-stained gel in sterile conditions and stored in ultrapure water at 4 °C. Protein sequencing was conducted by Eurogentec by the ESI-MS-MS analysis (Liege Science Park, Belgium). Weissella total DNA was prepared according to Robert et al. (2009) or using a DNA extraction kit (DNeasy Blood and Tissue kit, Qiagen) from overnight cultures grown in MRS medium. PCR amplifications were carried out using a Gradient Master Thermocycler (Eppendorf). Reactions were performed in a total volume of 20 μL containing 1 μL of template DNA (approximatively 5–10 ng), 1 × reaction buffer, 0.2 mM dNTP, 1.5 mM MgCl2, appropriate concentration of oligonucleotide primers (Sigma or Eurogentec) and 0.75 U RedGoldstar Taq polymerase (Eurogentec).