A systematic approach to study the pH-dependent release, productivity and product specificity of dextransucrases

Abstract

Background Dextransucrases are extracellular enzymes, which catalyze the formation of α-1→6-linked glucose polymers from sucrose. These enzymes are exclusively expressed by lactic acid bacteria, which commonly acidify the extracellular environment due to their physiology. Dextransucrases are thus confronted with steadily changing reaction conditions in regards to the environmental pH, which can further affect the amount of released dextransucrases. In this work, we studied the effect of the environmental pH on the release, the productivity and the product specificity of the dextransucrase expressed by Lactobacillus (L.) hordei TMW 1.1822. Dextransucrases were recovered as crude extracts at pH 3.5–pH 6.5 and then again used to produce dextrans at these pH values. The respectively produced dextran amounts and sizes were determined and the obtained results finally systematically correlated. Results Maximum dextran amounts were produced at pH 4.0 and pH 4.5, while the productivity of the dextransucrases significantly decreased at pH 3.5 and pH 6.5. The distribution of dextran amounts produced at different pH most likely reflects the pH dependent activity of the dextransucrases released by L. hordei, since different transglycosylation rates were determined at different pH using the same dextransucrase amounts. Moreover, similar hydrolysis activities were detected at all tested conditions despite significant losses of transglycosylation activities indicating initial hydrolysis prior to transglycosylation reactions. The molar masses and rms radii of dextrans increased up to pH 5.5 independently of the stability of the enzyme. The gelling properties of dextrans produced at pH 4.0 and pH 5.5 were different. Conclusions The presented methodological approach allows the controlled production of dextrans with varying properties and could be transferred and adapted to other microbes for systematic studies on the release and functionality of native sucrases or other extracellular enzymes.

Size-Dependent Variability in Flow and Viscoelastic Behavior of Levan Produced by Gluconobacter albidus TMW 2.1191

“…The yield, size and functional properties of levan from G. albidus TMW 2.1191 can be influenced by modulation of the environmental pH, as demonstrated in the present study and a previous study [20]. Similar findings were obtained for the dextran produced by Lactobacillus hordei TMW 1.1822 [33]. The environmental pH is, therefore, decisive to trigger the properties of uncharged, water-soluble high-molecular-weight exopolysaccharides produced by glucansucrases or fructansucrases [34].…”

Size-Dependent Rheological Variability of Levan Produced by Gluconobacter Albidus TMW 2.1191

“…The yield, size and functional properties of levan from G. albidus TMW 2.1191 can be influenced by modulation of the environmental pH as demonstrated in a previous study [19]. Similar findings were obtained for the dextran produced by Lactobacillus hordei TMW 1.1822 [30]. The environmental pH is hence decisive to trigger the properties of uncharged, water-soluble high-molecular weight exopolysaccharides produced by glucan-or fructansucrases [31].…”

Insights into the pH-dependent, extracellular sucrose utilization and concomitant levan formation by Gluconobacter albidus TMW 2.1191

“…However, little is known about the influencing factors of levansucrase release as well as of levansucrase activity, both of which are crucial for the efficiency of the complex production process of polydisperse levan taking place under continuously changing conditions. By application of the developed buffer system it was confirmed that the levansucrase is constitutively expressed by G. albidus TMW 2.1191 (without induction by its substrate sucrose) as reported for some dextransucrases secreted by water kefir LAB Schmid et al 2019). Higher volumetric levansucrase activities were detected in buffer supernatants at higher release pH (Fig.…”

“…A growth phase-dependent expression of levansucrases was also reported for the enteric bacterium Rahnella aquatilis (Seo et al 2002), at which it has to be considered that expression and secretion/release of sucrases are in fact independent processes. For instance, the water kefir isolate Lactobacillus hordei TMW 1.1822 releases its sucroseconverting dextransucrases in similar amounts into the environment in dependence of sucrose, but independently of the applied environmental release pH while accumulating the dextransucrases within the cell independent of sucrose Schmid et al 2019). In case of Lactobacillus hordei TMW 1.1822 it was further observed that the release pH affects the mean activity/productivity of the dextransucrase at different pH.…”