Lehrstuhl für Technische Mikrobiologie, Technische Universität München, Gregor-Mendel-Straße 4, 85354 Freising, Germany.
Karlsruhe Institute of Technology (KIT), Institute of Applied Biosciences, Department of Food Chemistry and Phytochemistry, 76131 Karlsruhe, Germany.
Int J Biol Macromol. 2018 Feb;107(Pt A):874-881. doi: 10.1016/j.ijbiomac.2017.09.063. Epub 2017 Sep 20.
Despite several hurdles, which hinder bacterial growth in beer, certain bacteria are still able to spoil beer. One type of spoilage is characterized by an increased viscosity and slimy texture caused by exopolysaccharide (EPS) formation of lactic acid bacteria (LAB). In this study, we characterize for the first time EPS production in a beer-spoiling strain (TMW 1.2112) of Lactobacillus brevis, a species commonly involved in beer spoilage. The strain's growth dynamics were assessed and we found an increased viscosity or ropiness in liquid or on solid media, respectively. Capsular polysaccharides (CPS) and released EPS from the cells or supernatant, respectively, were analyzed via NMR spectroscopy and methylation analysis. Both are identical β-(1→3)-glucans, which are ramified with β-glucose residues at position O2. Therefore, we assume that this EPS is mainly produced as CPS and partially released into the surrounding medium, causing viscosity of e.g. beer. CPS formation was confirmed via an agglutination test. A plasmid-located glycosyltransferase-2 was found as responsible for excess β-glucan formation, chromosomal glucanases were proposed for its degradation. The glycosyltransferase-2 gene could also be specifically identified in beer-spoiling, slime-producing Lactobacillus rossiae and Lactobacillus parabuchneri strains, suggesting it as promising marker gene for the early detection of β-glucan-producing Lactobacilli in breweries.
尽管有几个障碍会阻碍啤酒中细菌的生长,但某些细菌仍然能够使啤酒变质。一种变质类型的特征是由于形成了乳酸菌(LAB)的胞外多糖(EPS)而导致的粘度增加和粘稠质地。在这项研究中,我们首次对短乳杆菌(Lactobacillus brevis)啤酒变质菌株(TMW 1.2112)的 EPS 生产进行了特征描述,该菌株通常与啤酒变质有关。评估了该菌株的生长动态,我们发现其在液体或固体培养基中的粘度或粘性分别增加。通过 NMR 光谱和甲基化分析分别分析了细胞或上清液中的荚膜多糖(CPS)和释放的 EPS。它们都是相同的β-(1→3)-葡聚糖,在 O2 位置分支有β-葡萄糖残基。因此,我们假设这种 EPS 主要作为 CPS 产生,并部分释放到周围介质中,从而导致例如啤酒的粘度增加。通过凝集试验证实了 CPS 的形成。发现位于质粒上的糖基转移酶-2 负责过量β-葡聚糖的形成,提出了染色体葡聚糖酶对其进行降解。该糖基转移酶-2 基因也可以在啤酒变质、产粘液的罗斯氏乳杆菌(Lactobacillus rossiae)和毕赤氏乳杆菌(Lactobacillus parabuchneri)菌株中特异性识别,表明其作为在啤酒厂中早期检测产β-葡聚糖乳杆菌的有前途的标记基因。