College of Pharmacy and Research Institute of Drug Development, Chonnam National University, Gwangju, South Korea.
Department of Molecular Medicine, Chonnam National University, Gwangju, South Korea.
Front Cell Infect Microbiol. 2018 Mar 15;8:70. doi: 10.3389/fcimb.2018.00070. eCollection 2018.
The expression of virulence genes in bacteria is known to be regulated by various environmental and host factors. , an estuarine bacterium, experiences a dramatic environmental change during its infection process. We reported that RtxA1 toxin caused acute cell death only when close contact to host cells was allowed. A sigma factor RpoS is a very important regulator for the maximal survival of pathogens under stress conditions. Here, we studied the role of RpoS in cytotoxicity and mouse lethality. The growth of mutant strain was comparable to that of wild-type in heart infusion (HI) media and DMEM with HeLa cell lysate. An mutation resulted in decreased cytotoxicity, which was restored by complementation. Interestingly, host contact increased the expression and secretion of RtxA1 toxin, which was decreased and delayed by the mutation. Transcription of the cytotoxic gene and its transporter was significantly increased after host factor contact, whereas the activity was decreased by the mutation. In contrast, the mutation showed no effect on the transcriptional activity of a cytolytic heamolysin gene (). Additionally, the LD of the mutant was 15-fold higher than that of the wild-type in specific pathogen-free CD-1 female mice. Taken together, these results show that RpoS regulates the expression of RtxA1 toxin and its transporter upon host contact.
细菌的毒力基因表达已知受到各种环境和宿主因素的调节。作为一种河口细菌，在感染过程中经历了剧烈的环境变化。我们曾报道过，只有当与宿主细胞密切接触时，RtxA1 毒素才会导致急性细胞死亡。σ因子 RpoS 是病原体在应激条件下最大生存的重要调节剂。在这里，我们研究了 RpoS 在细胞毒性和小鼠致死性中的作用。突变株的生长在心脏输注（HI）培养基和含有 HeLa 细胞裂解物的 DMEM 中与野生型相当。一个 rpoS 突变导致细胞毒性降低，通过互补恢复了毒性。有趣的是，宿主接触增加了 RtxA1 毒素的表达和分泌，而 rpoS 突变则降低和延迟了毒素的表达和分泌。在宿主因子接触后，细胞毒性基因和其转运蛋白的转录显著增加，而活性则被 rpoS 突变降低。相比之下，rpoS 突变对细胞溶解素基因（）的转录活性没有影响。此外，在无特定病原体 CD-1 雌性小鼠中，突变株的 LD50 比野生型高 15 倍。综上所述，这些结果表明，RpoS 在与宿主接触时调节 RtxA1 毒素及其转运蛋白的表达。
