Li C, Motaleb A, Sal M, Goldstein S F, Charon N W
Department of Microbiology and Immunology, Health Sciences Center, West Virginia University, Morgantown 26506-9177, USA.
J Mol Microbiol Biotechnol. 2000 Oct;2(4):345-54.
Spirochetes have a unique structure, and as a result their motility is different from that of other bacteria. They also have a special attribute: spirochetes can swim in a highly viscous, gel-like medium, such as that found in connective tissue, that inhibits the motility of most other bacteria. In spirochetes, the organelles for motility, the periplasmic flagella, reside inside the cell within the periplasmic space. A given periplasmic flagellum is attached only at one end of the cell, and depending on the species, may or may not overlap in the center of the cell with those attached at the other end. The number of periplasmic flagella varies from species to species. These structures have been shown to be directly involved in spirochete motility, and they function by rotating within the periplasmic space. The mechanics of motility also vary among the spirochetes. In Leptospira, a motility model developed several years ago has been extensively tested, and the evidence supporting this model is convincing. Borrelia burgdorferi swims differently, and a model of its motility has been recently put forward. This model is based on analyzing the motion of swimming cells, high voltage electron microscopy of fixed cells, and mutant analysis. To better understand spirochete motility on a more molecular level, the proteins and genes involved in motility are being analyzed. Spirochete periplasmic flagellar filaments are among the most complex of bacterial flagella. They are composed of the FlaA sheath proteins, and in many species, multiple FlaB core proteins. Allelic exchange mutagenesis of the genes which encode these proteins is beginning to yield important information with respect to periplasmic flagellar structure and function. Although we are at an early stage with respect to analyzing the function, organization, and regulation of many of the genes involved in spirochete motility, unique aspects have already become evident. Future studies on spirochete motility should be exciting, as only recently have complete genome sequences and tools for allelic exchange mutagenesis become available.
螺旋体具有独特的结构，因此它们的运动方式与其他细菌不同。它们还有一个特殊的特性：螺旋体能够在高度黏稠的凝胶状介质中游动，比如在结缔组织中发现的那种介质，而这种介质会抑制大多数其他细菌的运动。在螺旋体中，负责运动的细胞器——周质鞭毛，位于细胞内的周质空间中。一条给定的周质鞭毛仅附着在细胞的一端，并且根据物种的不同，它可能会也可能不会在细胞中央与附着在另一端的鞭毛重叠。周质鞭毛的数量因物种而异。这些结构已被证明直接参与螺旋体的运动，并且它们通过在周质空间内旋转来发挥作用。不同螺旋体的运动机制也有所不同。在钩端螺旋体中，几年前建立的一个运动模型已经得到了广泛测试，支持该模型的证据很有说服力。伯氏疏螺旋体的游动方式不同，最近有人提出了其运动模型。这个模型是基于对游动细胞的运动分析、固定细胞的高压电子显微镜观察以及突变分析得出的。为了在分子水平上更好地理解螺旋体的运动，正在对参与运动的蛋白质和基因进行分析。螺旋体的周质鞭毛丝是细菌鞭毛中最为复杂的之一。它们由FlaA鞘蛋白组成，并且在许多物种中，还包含多种FlaB核心蛋白。对编码这些蛋白质的基因进行等位基因交换诱变，已开始产生有关周质鞭毛结构和功能的重要信息。尽管在分析许多参与螺旋体运动的基因的功能、组织和调控方面我们仍处于早期阶段，但独特的方面已经显现出来。未来关于螺旋体运动的研究应该会很令人兴奋，因为直到最近才获得了完整的基因组序列和等位基因交换诱变工具。
