Optical properties of microbial cells ans sensing the light direction in phototaxis

推动光合作用的阳光是地球上生命最重要的能源来源。光合蓝藻是叶绿体的祖先，它们仍然是几乎所有生境中非常重要的初级生产者。我们目前对蓝藻的生理和代谢的理解很大程度上是基于纯实验室培养的悬浮液的研究。此外，近年来的研究主要集中在这些富氧光养生物的光合作用和生物技术应用分析上。我们最近分析了蓝藻细胞的微光学特性，并揭示了这些物理细胞特性对感光光方向的重要性。此外，越来越多的证据表明，叶绿体的光学特性可能对优化弱光环境下的光合作用光收获很重要。球形蓝藻胞囊藻6803利用IV型菌毛在表面上移动或远离光源。单个细菌细胞就像一个非常有效的微透镜，将光源的清晰图像聚焦到细胞的另一侧（未被照亮）。这个明亮的光点局部触发了迄今为止尚未探索的信号转导链，然后控制细胞响应光源的运动。我们与其他微生物的初步调查表明，这种微光学效应并不局限于球形蓝藻，甚至光养生物。我们推测这些微光学效应可能对光传感、与环境的相互作用和紫外光损伤具有重要意义。为此，我们希望通过新的光学方法来探索蓝藻细胞的物理特性，并揭示从光感受器到运动机制的信号转导途径。在接近光波长的尺度上探测光学效应需要专门的物理知识。因此，我们开发了一个高度跨学科的项目，结合了物理学和（照片）生物学的互补技能。在第一种方法中，我们将使用物理和生物方法来测量非常小的细胞的光学特性。更一般地说，我们的目标是开发一种在单细胞尺度上以高光学分辨率探测分子对光刺激的反应的新方法。这将是产生单细胞生物定向光传感综合模型的基础。

Sunlight, which drives photosynthesis, is the most important energy supplier for life on Earth. Photosynthetic cyanobacteria are the ancestors of chloroplasts and they are still very important primary producers in almost all habitats. Our current understanding of the physiology and the metabolism of cyanobacteria is largely based on studies of pure lab-grown cultures in suspension. Moreover, studies in recent years have mainly focused on the analysis of photosynthesis and biotechnological applications of these oxygenic phototrophs. We recently analysed the micro-optic properties of cyanobacterial cells and revealed the importance of these physical cellular characteristics for sensing light direction for phototaxis. In addition, there is emerging evidence that the optical properties of chloroplasts might be important for optimizing photosynthetic light harvesting in low light environments. The spherical cyanobacterium Synechocystis 6803 moves on surfaces using type IV pili towards or away from a light source. The single bacterial cell acts as a very effective micro-lens, focusing a sharp image of the light source close to the opposite (non-illuminated) side of the cell. This bright light spot locally triggers a so far unexplored signal transduction chain, which then controls movement of the cell in response to the light source. Our preliminary investigations with other microorganisms indicate that such micro-optic effects are not confined to spherical cyanobacteria or even to phototrophs. We hypothesize that these micro-optic effects may have important implications for light-sensing, interaction with the environment and UV photodamage. For this proposal, we wish to explore physical properties of cyanobacterial cells by new optical methods and to reveal the signal transduction pathway from the photoreceptors to the motility machinery. Probing optical effects at scales close to wavelength of light requires specialized physical expertise. Therefore we have developed a highly interdisciplinary project combining complementary skills in physics and (photo)biology. In a first approach we will use physical and biological methods to measure the optical properties of very small cells. More generally, we aim to develop a new way to probe molecular responses to optical stimulation at the single-cell scale with high optical resolution. This will be the base for the generation of a comprehensive model for directional light sensing in single-celled organisms.