Many bacteria and archaea produce the polydisperse fructose polymer levan from sucrose upon biofilm formation via extracellular levansucrases (EC 2.4.1.10). We have investigated levansucrase-release and -activities as well as molecular size of the levan formed by the acetic acid bacterium Gluconobacter albidus TMW 2.1191 at varying environmental pH conditions to obtain insight in the ecological role of its constitutively expressed levansucrase and the produced levan. A buffer system was established enabling the recovery of levansucrase-containing supernatants from preincubated cell suspensions at pH 4.3-pH 5.7. The enzyme solutions were used to produce levans at different pH values and sucrose concentrations. Finally, the amounts and size distributions of the produced levans as well as the corresponding levansucrase activities were determined and correlated with each other. The data revealed that the levansucrase was released into the environment independently of its substrate sucrose, and that more levansucrase was released at pH ≥ 5.0. The glucose release and formation of high molecular weight levans (> 3.5 kDa) from 0.1 M initial sucrose was comparable between pH ~ 4.3-5.7 using equal amounts of released levansucrase. Hence, this type of levansucrase appears to be structurally adapted to changes in the extracellular pH and to exhibit a similar total activity over a wide acidic pH range, while it produced higher amounts of larger levan molecules at higher production pH and sucrose concentrations. These findings indicate the physiological adaptation of G. albidus TMW 2.1191 to efficient colonisation of sucrose-rich habitats via released levansucrases despite changing extracellular pH conditions in course of acid formation.

中文翻译：

---

深入了解浅白葡萄糖杆菌 TMW 2.1191 的 pH 依赖性细胞外蔗糖利用和伴随的果聚糖形成。


许多细菌和古细菌在通过细胞外果聚糖蔗糖酶形成生物膜时从蔗糖产生多分散果糖聚合物果聚糖（EC 2.4.1.10）。我们研究了醋酸菌 Gluconobacter albidus TMW 2.1191 在不同环境 pH 条件下的左聚蔗糖酶释放和活性以及左聚糖的分子大小，以深入了解其组成型表达的左聚蔗糖酶和产生的左聚糖的生态作用。建立了缓冲系统，能够从 pH 4.3-pH 5.7 预孵育的细胞悬浮液中回收含有果聚糖蔗糖酶的上清液。酶溶液用于在不同 pH 值和蔗糖浓度下生产果聚糖。最后，确定了产生的果聚糖的数量和尺寸分布以及相应的果聚糖蔗糖酶活性并相互关联。数据显示，左聚蔗糖酶独立于其底物蔗糖而释放到环境中，并且在pH≥5.0时释放更多的左聚蔗糖酶。使用等量释放的果聚糖蔗糖酶，葡萄糖的释放和从 0.1 M 初始蔗糖中形成高分子量果聚糖 (> 3.5 kDa) 在 pH ~ 4.3-5.7 之间是相当的。因此，这种类型的果聚糖蔗糖酶似乎在结构上适应了细胞外 pH 值的变化，并在较宽的酸性 pH 范围内表现出相似的总活性，同时它在较高的生产 pH 值和蔗糖浓度下产生更大量的较大果聚糖分子。这些发现表明，尽管在酸形成过程中细胞外 pH 条件发生了变化，但 G. albidus TMW 2.1191 通过释放的果聚糖蔗糖酶对富含蔗糖的栖息地进行了有效的定植。