The Origin of Rod Shape in Bacteria

生物学中一个尚待理解的基本问题是，细胞形状是如何遗传的？ 编码和酶促生成。球体和杆是最常见的形状， 有壁细菌由肽聚糖形成的细菌细胞壁在很大程度上决定了细胞的形状。当细菌 通过二分裂（分裂）繁殖，两个子细胞的形状已经由它们的 母细胞因此，很难使用健康的细菌细胞来探索细胞形状的起源。以 粘球菌细菌萌发期间球到棒形态转变的优势 xanthus，我们建议探讨潜在的机制，产生和维持的杆状细胞 形状. M. xanthus在不同的生命阶段在杆和球之间来回变化。罗德- 异形营养细胞彻底降解细胞壁，收缩成大小一致的球形细胞， 成熟为孢子。与芽孢杆菌的内生孢子形成不同，整个M. xanthus细胞转化为孢子。 以M. xanthus发芽，细胞重建它们的壁，并重新建立杆形状，而没有预先存在 模板这种独特的形态学转变提供了一个难得的机会，可视化从头细胞壁 合成（CWS）和细菌形态发生。为了解M. 因此，我们提出三个具体目标。首先，为了揭示萌发过程中从头CWS的机制， 我们将检验这样一个假设，即细胞壁生长的一种确定的模式是杆的建立所必需的。 形状第二，为了阐明MreB细胞骨架支持杆状的机制， 发芽，我们将测试的假设，MreB决定杆的形状，通过引导运动的CWS 机械.第三，揭示细胞极性对萌发过程中CWS和杆状的调控机制 孢子，我们将测试的假设，即细胞极性的建立是必要的球杆 过渡由于肽聚糖细胞壁在细菌中广泛保守，我们希望我们的结果 与m. xanthus将揭示形态发生的基本机制，这是很难研究在其他 细菌

A fundamental question in biology that remains to be understood is how cell shapes are genetically encoded and enzymatically generated. Spheres and rods are among the most common shapes adopted by walled bacteria. The bacterial cell wall, formed by peptidoglycan, largely determines cell shape. When bacteria reproduce by binary fission (division), the shapes of the two daughter cells are already determined by their mother cell. For this reason, it is difficult to explore the origin of cell shape using healthy bacterial cells. Taking advantage of a sphere-to-rod morphological transition during the germination of the bacterium Myxococcus xanthus, we propose to explore the mechanisms underlying the generation and maintenance of rod-like cell shapes. Cells of M. xanthus change back and forth between rods and spheres at different life stages. Rod- shaped vegetative cells thoroughly degrade their walls and shrink into uniformly sized spherical cells that then mature into spores. Unlike endospore formation in Bacillus species, whole M. xanthus cells convert to spores. As the spores of M. xanthus germinate, cells rebuild their walls and reestablish rod shape without preexisting templates. This unique morphological transition provides a rare opportunity to visualize de novo cell wall synthesis (CWS) and bacterial morphogenesis. To understand the mechanism of morphogenesis in M. xanthus, we propose three specific aims. First, to reveal the mechanism of de novo CWS during germination, we will test the hypothesis that a defined pattern of cell wall growth is required for the establishment of rod shape. Second, to elucidate the mechanism by which the MreB cytoskeleton supports rod shape during germination, we will test the hypothesis that MreB determines rod shape by guiding the motion of the CWS machinery. Third, to reveal the mechanism by which cell polarity regulates CWS and rod shape in germinating spores, we will test the hypothesis that the establishment of cell polarity is necessary for the sphere-to-rod transition. Because the peptidoglycan cell wall is widely conserved among bacteria, we expect that our results with M. xanthus will reveal fundamental mechanisms of morphogenesis, which is difficult to study in other bacteria.