Kobayashi Ayumu, Nakamura Masamune, Tsujii Masaru, Makino Kohei, Nagayama Tatsuya, Nakamura Kensuke, Nanatani Kei, Kota Kera, Furuuchi Yuki, Kayamori Shunsuke, Furuta Tadaomi, Suzuki Iwane, Hayakawa Yoshihiro, Tanudjaja Ellen, Ishimaru Yasuhiro, Uozumi Nobuyuki
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan.
School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
Mol Microbiol. 2023 May;119(5):599-611. doi: 10.1111/mmi.15057. Epub 2023 Mar 29.
Phototrophic bacteria face diurnal variations of environmental conditions such as light and osmolarity that affect their carbon metabolism and ability to generate organic compounds. The model cyanobacterium, Synechocystis sp. PCC 6803 forms a biofilm when it encounters extreme conditions like high salt stress, but the molecular mechanisms involved in perception of environmental changes that lead to biofilm formation are unknown. Here, we studied two two-component regulatory systems (TCSs) that contain diguanylate cyclases (DGCs), which produce the second messenger c-di-GMP, as potential components of the biofilm-inducing signaling pathway in Synechocystis. Analysis of single mutants provided evidence for involvement of the response regulators, Rre2 and Rre8 in biofilm formation. A bacterial two-hybrid assay showed that Rre2 and Rre8 each formed a TCS with a specific histidine kinase, Hik12 and Hik14, respectively. The in vitro assay showed that Rre2 had DGC activity regardless of its de/phosphorylation status, whereas Rre8 required phosphorylation for DGC activity. Hik14-Rre8 likely functioned as an inducible sensing system in response to environmental change. Biofilm assays with Synechocystis mutants suggested that pairs of hik12-rre2 and hik14-rre8 responded to high salinity-induced biofilm formation. Inactivation of hik12-rre2 and hik14-rre8 did not affect the performance of the light reactions of photosynthesis. These data suggest that Hik12-Rre2 and Hik14-Rre8 participate in biofilm formation in Synechocystis by regulating c-di-GMP production via the DGC activity of Rre2 and Rre8.
光合细菌面临着诸如光照和渗透压等环境条件的昼夜变化，这些变化会影响它们的碳代谢以及产生有机化合物的能力。模式蓝细菌聚球藻属6803菌株（Synechocystis sp. PCC 6803）在遇到高盐胁迫等极端条件时会形成生物膜，但导致生物膜形成的环境变化感知所涉及的分子机制尚不清楚。在此，我们研究了两个包含二鸟苷酸环化酶（DGCs）的双组分调节系统（TCSs），二鸟苷酸环化酶可产生第二信使环二鸟苷单磷酸（c-di-GMP），作为聚球藻属生物膜诱导信号通路的潜在组成部分。对单突变体的分析为响应调节因子Rre2和Rre8参与生物膜形成提供了证据。细菌双杂交试验表明，Rre2和Rre8分别与特定的组氨酸激酶Hik12和Hik14形成一个双组分调节系统。体外试验表明，无论Rre2的去磷酸化/磷酸化状态如何，它都具有二鸟苷酸环化酶活性，而Rre8的二鸟苷酸环化酶活性需要磷酸化。Hik14-Rre8可能作为一种诱导感应系统来响应环境变化。聚球藻属突变体的生物膜试验表明，hik12-rre2和hik14-rre8对高盐诱导的生物膜形成有反应。hik12-rre2和hik14-rre8的失活并不影响光合作用光反应的性能。这些数据表明，Hik12-Rre2和Hik14-Rre8通过Rre2和Rre8的二鸟苷酸环化酶活性调节c-di-GMP的产生，从而参与聚球藻属的生物膜形成。
