Lehrstuhl für Technische Mikrobiologie, Technische Universität München, Freising, Germany.
Karlsruhe Institute of Technology (KIT), Institute of Applied Biosciences, Karlsruhe, Germany.
Int J Biol Macromol. 2018 Aug;115:236-242. doi: 10.1016/j.ijbiomac.2018.04.068. Epub 2018 Apr 13.
Water kefir granules are supposed to mainly consist of dextrans produced by Lactobacillus (L.) hilgardii. Still, other microorganisms such as L. hordei, L. nagelii, Leuconostoc (Lc.) citreum and Saccharomyces (S.) cerevisiae are commonly isolated from water kefir granules, while their contribution to the granule formation remains unknown. We studied putative functions of these microbes in granule formation, upon development of a simplified model system containing hydrophilic object slides, which mimics the hydrophilic surface of a growing kefir granule. We found that all tested lactic acid bacteria produced glucans, while solely those isolated from the four different L. hordei strains induced yeast aggregation on the hydrophilic slides. Therefore, structural differences between these glucans were investigated with respect to their size distributions and their linkage types. Beyond the finding that all glucans were identified as dextrans, those of the four L. hordei strains were highly similar among each other regarding portions of linkage types and size distributions. Thus, our study suggests the specific size and structural organization of the dextran produced by L. hordei as the main cause for inducing S. cerevisiae aggregation and network formation on hydrophilic surfaces and thus as crucial initiation of the stepwise water kefir granule growth.
水发酵粒主要由乳杆菌（Lactobacillus）（L.）hilgardii 产生的葡聚糖组成。然而，其他微生物，如 L. hordei、L. nagelii、Leuconostoc（Lc.）citreum 和 Saccharomyces（S.）cerevisiae，通常从水发酵粒中分离出来，但其对粒形成的贡献尚不清楚。我们研究了这些微生物在颗粒形成中的可能作用，开发了一种简化的模型系统，其中包含亲水物体载玻片，模拟正在生长的发酵粒的亲水表面。我们发现所有测试的乳酸菌都产生葡聚糖，而仅从四种不同的 L. hordei 菌株中分离出的那些会在亲水载玻片上诱导酵母聚集。因此，我们研究了这些葡聚糖的大小分布和键合类型，以了解它们之间的结构差异。除了发现所有葡聚糖均被鉴定为葡聚糖外，这四种 L. hordei 菌株的葡聚糖在键合类型和大小分布的部分方面非常相似。因此，我们的研究表明，L. hordei 产生的葡聚糖的特定大小和结构组织是诱导 S. cerevisiae 聚集和在亲水表面形成网络的主要原因，从而是水发酵粒逐步生长的关键起始步骤。
