The probiotic Lactobacillus brevis KB290 is a natural producer of cell-bound exopolysaccharide (EPS), and the plasmid-encoded glycosyltransferase genes are responsible for this EPS production. KB290 forms unique rugose colonies inside an agar medium; this characteristic is useful for detecting and enumerating KB290 in the gut or feces. However, the genetic elements associated with this morphology remain unclear. Here, we aimed to investigate the relation between the plasmid eps genes and rugose colony morphology in KB290. The plasmid-cured mutants formed smooth colonies, and the rugose colony morphology was restored after complementation with the eps genes. The eps genes were successfully cloned and expressed in other L. brevis and L. plantarum strains. In these transformant strains, the presence of the EPS, consisting of glucose and N-acetylglucosamine, correlated with rugose colonies, indicating that EPS is responsible for rugose colony formation. To the best of our knowledge, this is the first report identifying the genetic factors influencing rugose colonies in Lactobacillus strains. This rugose colony formation may serve as a useful selective marker for KB290 in routine laboratory and research settings and can be used to detect the spontaneous loss of plasmids in this strain.

中文翻译：

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益生菌短乳杆菌KB290中通过质粒编码基因产生的细胞结合胞外多糖产生与皱纹菌落形态之间的关系。

益生菌短乳杆菌KB290是细胞结合胞外多糖（EPS）的天然产生者，而质粒编码的糖基转移酶基因则负责这种EPS的产生。KB290在琼脂培养基中形成独特的皱纹菌落。此特征对于检测和枚举肠道或粪便中的KB290非常有用。但是，与这种形态有关的遗传因素仍然不清楚。在这里，我们旨在调查质粒eps290基因和KB290中的皱纹菌落形态之间的关系。质粒固化的突变体形成平滑的菌落，并且在与eps基因互补后恢复了皱纹菌落的形态。eps基因已成功克隆并在其他短乳杆菌和植物乳杆菌菌株中表达。在这些转化株中，EPS的存在 由葡萄糖和N-乙酰氨基葡萄糖组成，与皱纹菌落相关，表明EPS负责皱纹菌落的形成。据我们所知，这是第一个鉴定影响乳杆菌菌株中皱纹菌落的遗传因素的报告。这种皱纹菌落的形成可在常规实验室和研究环境中用作KB290的有用选择标记，并可用于检测该菌株中质粒的自发丢失。