Department of Engineering Science, Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo, Japan.
Institute of Biology III, University of Freiburg, Freiburg, Germany.
Elife. 2022 May 10;11:e73405. doi: 10.7554/eLife.73405.
Many cyanobacteria, which use light as an energy source via photosynthesis, show directional movement towards or away from a light source. However, the molecular and cell biological mechanisms for switching the direction of movement remain unclear. Here, we visualized type IV pilus-dependent cell movement in the rod-shaped thermophilic cyanobacterium using optical microscopy at physiological temperature and light conditions. Positive and negative phototaxis were controlled on a short time scale of 1 min. The cells smoothly moved over solid surfaces towards green light, but the direction was switched to backward movement when we applied additional blue light illumination. The switching was mediated by three photoreceptors, SesA, SesB, and SesC, which have cyanobacteriochrome photosensory domains and synthesis/degradation activity of the bacterial second messenger cyclic dimeric GMP (c-di-GMP). Our results suggest that the decision-making process for directional switching in phototaxis involves light-dependent changes in the cellular concentration of c-di-GMP. Direct visualization of type IV pilus filaments revealed that rod-shaped cells can move perpendicular to the light vector, indicating that the polarity can be controlled not only by pole-to-pole regulation but also within-a-pole regulation. This study provides insights into previously undescribed rapid bacterial polarity regulation via second messenger signalling with high spatial resolution.
许多利用光合作用将光作为能源的蓝藻表现出朝向或远离光源的定向运动。然而，用于切换运动方向的分子和细胞生物学机制尚不清楚。在这里，我们使用光学显微镜在生理温度和光照条件下可视化了杆状嗜热蓝藻中依赖于 IV 型菌毛的细胞运动。正、负趋光性可以在 1 分钟的短时间尺度内得到控制。细胞在固体表面上平稳地向绿光移动，但当我们施加额外的蓝光照射时，方向会切换到向后移动。这种切换是由三个光受体 SesA、SesB 和 SesC 介导的，它们具有细菌第二信使环二鸟苷酸（c-di-GMP）的合成/降解活性和蓝藻菌视紫红质感光结构域。我们的结果表明，趋光性中定向切换的决策过程涉及细胞内 c-di-GMP 浓度的光依赖性变化。对 IV 型菌毛丝的直接可视化显示，杆状细胞可以垂直于光矢量移动，这表明极性不仅可以通过极对极调节来控制，也可以通过极内调节来控制。这项研究提供了对以前未描述的通过第二信使信号进行快速细菌极性调控的新见解，具有高空间分辨率。
