Oxygen‐dependent regulation of SPI1 type three secretion system by small RNAs in Salmonella enterica serovar Typhimurium

• Published in: Molecular microbiology 2019-03, Vol.111 (3), p.570-587
• Main Authors: Kim, Kyungsub, Golubeva, Yekaterina A., Vanderpool, Carin K., Slauch, James M.
• Format: Article
• Language: English
• Subjects: 5' Untranslated Regions; Aeration; Animals; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Clonal deletion; Diarrhea; DNA Mutational Analysis; Epithelial cells; Gene Deletion; Gene Expression; Gene Expression Regulation, Bacterial - drug effects; Gene Regulatory Networks; Inflammation; Intestine; Mice; Nucleic Acid Hybridization; Oral infection; Oxygen; Oxygen - metabolism; Pathogenicity; Pathogens; Phenotypes; Regulation; RNA, Messenger - metabolism; RNA, Small Untranslated - genetics; RNA, Small Untranslated - metabolism; Salmonella; Salmonella typhimurium - drug effects; Salmonella typhimurium - genetics; Secretion; Transcription; Transcription Factors - genetics; Transcription Factors - metabolism; Translation; Type III Secretion Systems - biosynthesis; Type III Secretion Systems - genetics
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14174

Summary Salmonella Typhimurium induces inflammatory diarrhea and uptake into intestinal epithelial cells using the Salmonella pathogenicity island 1 (SPI1) type III secretion system (T3SS). Three AraC‐like regulators, HilD, HilC and RtsA, form a feed‐forward regulatory loop that activates transcription of hilA, encoding the activator of the T3SS structural genes. Many environmental signals and regulatory systems are integrated into this circuit to precisely regulate SPI1 expression. A subset of these regulatory factors affects translation of hilD, but the mechanisms are poorly understood. Here, we identified two sRNAs, FnrS and ArcZ, which repress hilD translation, leading to decreased production of HilA. FnrS and ArcZ are oppositely regulated in response to oxygen, one of the key environmental signals affecting expression of SPI1. Mutational analysis demonstrates that FnrS and ArcZ bind to the hilD mRNA 5′ UTR, resulting in translational repression. Deletion of fnrS led to increased HilD production under low‐aeration conditions, whereas deletion of arcZ abolished the regulatory effect on hilD translation aerobically. The fnrS arcZ double mutant has phenotypes in a mouse oral infection model consistent with increased expression of SPI1. Together, these results suggest that coordinated regulation by these two sRNAs maximizes HilD production at an intermediate level of oxygen. Salmonella is a leading cause of gastrointestinal disease worldwide. Proper temporal and spatial expression of the Salmonella SPI1 type three secretion system is critical for invasion of the host intestinal epithelium. Here, we show that two oxygen‐dependent sRNAs, FnrS and ArcZ, regulate production of the invasion machinery, tuning SPI1 expression to a particular oxygen level consistent with that at the epithelial surface.