UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA.
UT-ORNL Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
Biochim Biophys Acta Biomembr. 2019 Jul 1;1861(7):1338-1345. doi: 10.1016/j.bbamem.2019.05.009. Epub 2019 May 14.
Bacterial membranes are complex mixtures of lipids and proteins, the combination of which confers biophysical properties that allows cells to respond to environmental conditions. Carotenoids are sterol analogs that are important for regulating membrane dynamics. The membrane of Pantoea sp. YR343 is characterized by the presence of the carotenoid zeaxanthin, and a carotenoid-deficient mutant, ΔcrtB, displays defects in root colonization, reduced secretion of indole-3-acetic acid, and defects in biofilm formation. Here we demonstrate that the loss of carotenoids results in changes to the membrane lipid composition in Pantoea sp. YR343, including increased amounts of unsaturated fatty acids in the ΔcrtB mutant membranes. These mutant cells displayed less fluid membranes in comparison to wild type cells as measured by fluorescence anisotropy of whole cells. Studies with artificial systems, however, have shown that carotenoids impart membrane rigidifying properties. Thus, we examined membrane fluidity using spheroplasts and vesicles composed of lipids extracted from either wild type or mutant cells. Interestingly, with the removal of the cell wall and membrane proteins, ΔcrtB vesicles were more fluid than vesicles made from lipids extracted from wild type cells. In addition, carotenoids appeared to stabilize membrane fluidity during rapidly changing temperatures. Taken together, these results suggest that Pantoea sp. YR343 compensates for the loss of carotenoids by changing lipid composition, which together with membrane proteins, results in reduced membrane fluidity. These changes may influence the abundance or function of membrane proteins that are responsible for the physiological changes observed in the ΔcrtB mutant cells.
细菌膜是由脂质和蛋白质组成的复杂混合物，其组合赋予了赋予细胞对环境条件做出响应的生物物理特性。类胡萝卜素是固醇类似物，对于调节膜动力学非常重要。 Pantoea sp. YR343 的膜的特征在于存在类胡萝卜素玉米黄质，并且类胡萝卜素缺陷突变体ΔcrtB 在根定植、吲哚-3-乙酸分泌减少和生物膜形成缺陷方面表现出缺陷。在这里，我们证明类胡萝卜素的缺失导致 Pantoea sp. YR343 中膜脂组成发生变化，包括ΔcrtB 突变体膜中不饱和脂肪酸的含量增加。与野生型细胞相比，这些突变细胞显示出较少的流动膜，如通过全细胞荧光各向异性测量。然而，使用人工系统的研究表明，类胡萝卜素赋予膜刚性特性。因此，我们使用来自野生型或突变细胞提取的脂质制成的原生质体和囊泡来检查膜流动性。有趣的是，去除细胞壁和膜蛋白后，与从野生型细胞提取的脂质制成的囊泡相比，ΔcrtB 囊泡具有更高的流动性。此外，类胡萝卜素似乎在快速变化的温度下稳定了膜流动性。总之，这些结果表明，Pantoea sp. YR343 通过改变脂质组成来补偿类胡萝卜素的缺失，这与膜蛋白一起导致膜流动性降低。这些变化可能会影响负责观察到的ΔcrtB 突变体细胞中生理变化的膜蛋白的丰度或功能。
