Molecular Genetics of Prokaryotes, Institute of Biology III, University of Freiburg, Freiburg, Germany.
Research Core Unit Metabolomics, Hannover Medical School, Hannover, Germany.
Photochem Photobiol Sci. 2020 May 1;19(5):631-643. doi: 10.1039/c9pp00489k. Epub 2020 Apr 7.
The cyanobacterial phytochrome Cph2 is a light-dependent diguanylate cyclase of the cyanobacterium Synechocystis 6803. Under blue light, Cph2-dependent increase in the cellular c-di-GMP concentration leads to inhibition of surface motility and enhanced flocculation of cells in liquid culture. However, the targets of second messenger signalling in this cyanobacterium and its mechanism of action remained unclear. Here, we determined the cellular concentrations of cAMP and c-di-GMP in wild-type and Δcph2 cells after exposure to blue and green light. Inactivation of cph2 completely abolished the blue-light dependent increase in c-di-GMP content. Therefore, a microarray analysis with blue-light grown wild-type and Δcph2 mutant cells was used to identify c-di-GMP dependent alterations in transcript accumulation. The increase in the c-di-GMP content alters expression of genes encoding putative cell appendages, minor pilins and components of chemotaxis systems. The mRNA encoding the minor pilins pilA5-pilA6 was negatively affected by high c-di-GMP content under blue light, whereas the minor pilin encoding operon pilA9-slr2019 accumulates under these conditions, suggesting opposing functions of the respective gene sets. Artificial overproduction of c-di-GMP leads to similar changes in minor pilin gene expression and supports previous findings that c-di-GMP is important for flocculation via the function of minor pilins. Mutational and gene expression analysis further suggest that SyCRP2, a CRP-like transcription factor, is involved in regulation of minor pilin and putative chaperone usher pili gene expression.
蓝藻藻青蛋白 Cph2 是集胞藻 6803 的一种光依赖性双鸟苷酸环化酶。在蓝光下，Cph2 依赖性的细胞中二鸟苷酸（c-di-GMP）浓度增加导致表面运动抑制和液体培养中细胞絮凝增强。然而，该蓝藻中二信使信号的靶标及其作用机制仍不清楚。在这里，我们在暴露于蓝光和绿光后，测定了野生型和Δcph2 细胞中的 cAMP 和 c-di-GMP 的细胞浓度。cph2 的失活完全消除了 c-di-GMP 含量的蓝光依赖性增加。因此，使用经过蓝光生长的野生型和Δcph2 突变细胞的微阵列分析来鉴定 c-di-GMP 依赖性转录物积累的改变。c-di-GMP 含量的增加改变了编码假定细胞附属物、小菌毛和趋化系统组件的基因的表达。在蓝光下，高 c-di-GMP 含量会负调控编码小菌毛 pilA5-pilA6 的 mRNA，而在这些条件下，编码小菌毛的操纵子 pilA9-slr2019 积累，表明各自基因集具有相反的功能。人工过表达 c-di-GMP 会导致小菌毛基因表达发生类似变化，并支持先前的发现，即 c-di-GMP 通过小菌毛的功能对絮凝很重要。突变和基因表达分析进一步表明，CRP 样转录因子 SyCRP2 参与小菌毛和假定伴侣菌毛基因表达的调节。
