Fig. 1

Overview of the experimental setups used to characterize dextran production at different pH. Cells were grown in 53 mL mMRS medium (without sucrose) for 18 h, split up to 7.5 mL samples, centrifuged and re-dissolved in 7.5 mL buffer (0.1 M Na₂HPO₄/0.1 M citric acid + 0.1 M sucrose) of the desired pH values, respectively. In setup (a), dextransucrase containing supernatants were collected at pH 3.5 to 6.5, while in setup (b) the release pH for all samples was kept constant at pH 4.5. After 3.0 h of incubation in these buffers, the cells were removed by centrifugation and the supernatants were sterile-filtered. 7.5 mL buffer of the required pH to reach the final production pH were added, followed by 24 h of incubation and subsequent dextran quantification. Bars indicate the produced dextran amounts in g/L, which were either determined gravimetrically (isolated dextran) or via calculation of the totally produced amount using the calculated transglycosylation activity (24 h). Data are expressed with mean ± SD of three biological replicates