Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China.
PLoS One. 2011;6(8):e23701. doi: 10.1371/journal.pone.0023701. Epub 2011 Aug 23.
EnvZ and OmpR constitute the bacterial two-component signal transduction system known to mediate osmotic stress response in a number of gram-negative bacteria. In an effort to understand the mechanism through which Shewanella oneidensis senses and responds to environmental osmolarity changes, structure of the ompR-envZ operon was determined with Northern blotting assay and roles of the EnvZ/OmpR two-component system in response to various stresses were investigated with mutational analysis, quantitative reverse transcriptase PCR (qRT-PCR), and phenotype microarrays. Results from the mutational analysis and qRT-PCR suggested that the EnvZ/OmpR system contributed to osmotic stress response of S. oneidensis and very likely engaged a similar strategy employed by E. coli, which involved reciprocal regulation of two major porin coding genes. Additionally, the ompR-envZ system was also found related to cell motility. We further showed that the ompR-envZ dependent regulation of porin genes and motility resided almost completely on ompR and only partially on envZ, indicating additional mechanisms for OmpR phosphorylation. In contrast to E. coli lacking ompR-envZ, however, growth of S. oneidensis did not show a significant dependence on ompR-envZ even under osmotic stress. Further analysis with phenotype microarrays revealed that the S. oneidensis strains lacking a complete ompR-envZ system displayed hypersensitivities to a number of agents, especially in alkaline environment. Taken together, our results suggest that the function of the ompR-envZ system in S. oneidensis, although still connected with osmoregulation, has diverged considerably from that of E. coli. Additional mechanism must exist to support growth of S. oneidensis under osmotic stress.
EnvZ 和 OmpR 构成了细菌双组分信号转导系统，已知该系统介导许多革兰氏阴性细菌的渗透胁迫反应。为了了解 Shewanella oneidensis 感应和响应环境渗透压变化的机制，我们通过 Northern 印迹分析确定了 ompR-envZ 操纵子的结构，并通过突变分析、定量逆转录 PCR（qRT-PCR）和表型微阵列研究了 EnvZ/OmpR 二组分系统在应对各种应激时的作用。突变分析和 qRT-PCR 的结果表明，EnvZ/OmpR 系统有助于 S. oneidensis 的渗透胁迫反应，并且很可能采用了与大肠杆菌相似的策略，涉及到两个主要孔蛋白编码基因的相互调节。此外，我们还发现 ompR-envZ 系统与细胞运动有关。我们进一步表明，ompR-envZ 依赖于孔蛋白基因和运动的调节几乎完全依赖于 ompR，而仅部分依赖于 envZ，表明 OmpR 磷酸化的其他机制。然而，与缺乏 ompR-envZ 的大肠杆菌不同，即使在渗透胁迫下，S. oneidensis 的生长也没有表现出对 ompR-envZ 的显著依赖性。通过表型微阵列的进一步分析表明，缺乏完整的 ompR-envZ 系统的 S. oneidensis 菌株对许多试剂表现出敏感性，尤其是在碱性环境中。总之，我们的结果表明，尽管 ompR-envZ 系统在 S. oneidensis 中的功能仍然与渗透压调节有关，但与大肠杆菌的功能已经有了很大的不同。必须存在其他机制来支持 S. oneidensis 在渗透压胁迫下的生长。
