A light-triggered behavioural switch in cyanobacterial motility

蓝细菌是一种光合作用的原核生物。它们是所有植物和藻类叶绿体的祖先。除了将它们用作产氧光合作用的模式生物外，由于它们在生物技术应用方面的潜力，公众对它们的兴趣越来越大。与所有光养生物一样，光感对于蓝藻适应不同的环境条件至关重要。因此，它们必须选择最佳的光条件来吸收光子用于光合能量供应，同时避免强光和紫外光胁迫。这就需要在不同光照条件下进行有效的适应策略。集胞藻6803的光感受器Cph 2通过两个不同的感光模块感受四种不同的颜色。光信号被转导至合成或降解第二信使分子c-di-GMP的酶活性效应子模块。根据这种分子的浓度，蓝细菌决定是否向光源移动或诱导生物膜形成。我们已经证明，多域传感器Cph 2改变了蓝光下蓝藻细胞中的c-di-GMP水平，从而抑制了对这些不利的光条件的趋光性。虽然红光/远红光吸收光敏色素模块的结构已经解决，但我们仍然不了解这部分光开关的生物功能。在项目提案中，我们希望阐明Cph 2感测到的不同光信号如何整合并传输到控制蓝藻运动的c-di-GMP相关信号转导链的下游组件。此外，我们希望确定未知的c-di-GMP效应蛋白，并分析其在调节运动中的作用。我们将使用重组蛋白的光谱分析，蛋白质相互作用的研究，光遗传学工具和趋光性测试与各种突变株的监管和结构元件，以解开潜在的分子机制的Cph 2为基础的信号转导过程中的蓝藻模型菌株。

Cyanobacteria are phototrophic prokaryotes performing plant-like photosynthesis. They are the ancestors of all plant and algae chloroplasts. Besides using them as model organisms for oxygenic photosynthesis there is an increasing interest in the public because of their potential for biotechnological applications. Like for all phototrophs light sensing is of crucial importance for cyanobacteria to acclimate to different environmental conditions. Accordingly, they have to choose the optimal light conditions to absorb photons for photosynthetic energy supply and at the same time to avoid high- and UV-light stress. This requires efficient acclimation strategies for grow under different light conditions. The photoreceptor Cph2 from Synechocystis sp. PCC 6803 senses four different colours by harbouring two distinct photosensory modules. The light signals are transduced to the enzymatically active effector modules which synthesize or degrade the second messenger molecule c-di-GMP. Depending on the concentration of this molecule cyanobacteria decide whether to move towards a light source or to induce biofilm formation. We have demonstrated that the multi-domain sensor Cph2 alters the c-di-GMP level in cyanobacterial cells under blue light, thus inhibiting phototaxis towards these unfavourable light conditions. Though the structure of the red/far-red absorbing phytochrome module has been solved, we still do not understand the biological function of this part of the light switch. In the project proposal we want to elucidate how the different light signals sensed by Cph2 are integrated and transmitted to downstream components of a c-di-GMP related signal transduction chain that controls cyanobacterial motility. Further we want to identify the unknown c-di-GMP effector proteins and to analyze their roles in regulating motility. We will use spectroscopic analysis of recombinant proteins, protein interaction studies, optogenetic tools and phototaxis tests with various mutant strains of regulatory and structural elements to unravel the underlying molecular mechanism of Cph2 based signaling processes in the cyanobacterial model strain.