AUTHOR=Yang Guang , Li Boan , Jia Leili , Qiu Huaiyu , Yang Mingjuan , Zhu Binghua , Xie Jing , Qiu Shaofu , Li Peng , Ma Hui , Song Hongbin , Wang Ligui 

TITLE=A Novel sRNA in Shigella flexneri That Regulates Tolerance and Virulence Under Hyperosmotic Pressure

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2020.00483

DOI=10.3389/fcimb.2020.00483

ISSN=2235-2988

ABSTRACT=<p>Regulation of the environmental stress response and virulence of <italic>Shigella flexneri</italic> may involve multiple signaling pathways; however, these mechanisms are not well-defined. In bacteria, small regulatory RNAs (sRNAs) regulate bacterial growth, metabolism, virulence, and environmental stress response. Therefore, identifying novel functional sRNAs in <italic>S. flexneri</italic> could help elucidate pathogenic adaptations to host micro-environmental stresses and associated virulence. The aim of this study was to confirm the presence of an sRNA, <italic>Ssr54</italic>, in <italic>S. flexneri</italic> and to determine its functions and possible mechanism of action. <italic>Ssr54</italic> was found to regulate tolerance and virulence under hyperosmotic pressure. Its expression was verified by qRT-PCR and Northern blotting, and its genomic position was confirmed by 5′-rapid amplification of cDNA ends. <italic>Ssr54</italic> expression was significantly decreased (~ 80%) under hyperosmotic conditions (680 mM NaCl), and the survival rate of the <italic>Ssr54</italic> deletion strain increased by 20% under these conditions. This suggested that <italic>Ssr54</italic> has been selected to promote host survival under hyperosmotic conditions. Additionally, virulence assessment, including guinea pig Sereny test and competitive invasion assays in mouse lungs, revealed that <italic>Ssr54</italic> deletion significantly decreased <italic>S. flexneri</italic> virulence. Two-dimensional gel analyses suggest that <italic>Ssr54</italic> may modulate the expression of <italic>tolC, ompA</italic>, and <italic>treF</italic> genes, which may affect the virulence and survival of <italic>S. flexneri</italic> under osmotic pressures. Furthermore, <italic>treF</italic> expression has been shown to improve the survival of <italic>S. flexneri</italic> under osmotic pressures. These results suggest that <italic>Ssr54</italic> has a broad range of action in <italic>S. flexneri</italic> response to hyperosmotic environmental stresses and in controlling its virulence to adapt to environmental stresses encountered during host infection.</p>