Brandt Julia U, Born Friederike-Leonie, Jakob Frank, Vogel Rudi F
Technische Universität München, Lehrstuhl für Technische Mikrobiologie, Gregor-Mendel-Straße 4, 85354, Freising, Germany.
BMC Microbiol. 2017 Aug 10;17(1):172. doi: 10.1186/s12866-017-1070-y.
Kozakia baliensis NBRC 16680 secretes a gum-cluster derived heteropolysaccharide and forms a surface pellicle composed of polysaccharides during static cultivation. Furthermore, this strain exhibits two colony types on agar plates; smooth wild-type (S) and rough mutant colonies (R). This switch is caused by a spontaneous transposon insertion into the gumD gene of the gum-cluster, resulting in a heteropolysaccharide secretion deficient, rough phenotype. To elucidate, whether this is a directed switch triggered by environmental factors, we checked the number of R and S colonies under different growth conditions including ethanol and acetic acid supplementation. Furthermore, we investigated the tolerance of R and S strains against ethanol and acetic acid in shaking and static growth experiments. To get new insights into the composition and function of the pellicle polysaccharide, the polE gene of the R strain was additionally deleted, as it was reported to be involved in pellicle formation in other acetic acid bacteria.
The number of R colonies was significantly increased upon growth on acetic acid and especially ethanol. The morphological change from K. baliensis NBRC 16680 S to R strain was accompanied by changes in the sugar contents of the produced pellicle EPS. The R:ΔpolE mutant strain was not able to form a regular pellicle anymore, but secreted an EPS into the medium, which exhibited a similar sugar monomer composition as the pellicle polysaccharide isolated from the R strain. The R strain had a markedly increased tolerance towards acetic acid and ethanol compared to the other NBRC 16680 strains (S, R:ΔpolE). A relatively high intrinsic acetic acid tolerance was also observable for K. baliensis DSM 14400, which might indicate diverse adaptation mechanisms of different K. baliensis strains in altering natural habitats.
The results suggest that the genetically triggered R phenotype formation is directly related to increased acetic acid and ethanol tolerance. The polE gene turned out to be involved in the formation of a cell-associated, capsular polysaccharide, which seems to be essential for increased ethanol/acetic tolerance in contrast to the secreted gum-cluster derived heteropolysaccharide. The genetic and morphological switch could represent an adaptive evolutionary step during the development of K. baliensis NBRC 16680 in course of changing environmental conditions.
巴厘岛科扎基亚菌（Kozakia baliensis）NBRC 16680在静置培养过程中分泌一种源自糖胶簇的杂多糖，并形成由多糖组成的表面菌膜。此外，该菌株在琼脂平板上表现出两种菌落类型；光滑的野生型（S）和粗糙的突变菌落（R）。这种转变是由转座子自发插入糖胶簇的gumD基因引起的，导致杂多糖分泌缺陷的粗糙表型。为了阐明这是否是由环境因素触发的定向转变，我们检查了在包括添加乙醇和乙酸在内的不同生长条件下R和S菌落的数量。此外，我们在振荡和静置生长实验中研究了R和S菌株对乙醇和乙酸的耐受性。为了深入了解菌膜多糖的组成和功能，R菌株的polE基因被额外删除，因为据报道它参与了其他醋酸菌的菌膜形成。
在乙酸尤其是乙醇上生长时，R菌落的数量显著增加。巴厘岛科扎基亚菌NBRC 16680从S型到R型的形态变化伴随着所产生的菌膜胞外多糖糖含量的变化。R:ΔpolE突变菌株不再能够形成规则的菌膜，但向培养基中分泌了一种胞外多糖，其糖单体组成与从R菌株分离的菌膜多糖相似。与其他NBRC 16680菌株（S、R:ΔpolE）相比，R菌株对乙酸和乙醇的耐受性明显增强。巴厘岛科扎基亚菌DSM 14400也表现出相对较高的固有乙酸耐受性，这可能表明不同的巴厘岛科扎基亚菌株在改变自然栖息地时有不同的适应机制。
结果表明，基因触发的R表型形成与乙酸和乙醇耐受性的增加直接相关。结果表明，polE基因参与了细胞相关的荚膜多糖的形成，与分泌的源自糖胶簇的杂多糖相比，它似乎是提高乙醇/乙酸耐受性所必需的。这种遗传和形态转变可能代表了巴厘岛科扎基亚菌NBRC 16680在不断变化的环境条件下进化过程中的一个适应性进化步骤。
