AUTHOR=Wang Ligui , Yang Guang , Qi Lihua , Li Xiang , Jia Leili , Xie Jing , Qiu Shaofu , Li Peng , Hao RongZhang , Wu Zhihao , Du Xinying , Li Wuju , Song Hongbin 

TITLE=A Novel Small RNA Regulates Tolerance and Virulence in Shigella flexneri by Responding to Acidic Environmental Changes

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2016.00024

DOI=10.3389/fcimb.2016.00024

ISSN=2235-2988

ABSTRACT=<p><italic>Shigella flexneri</italic> is an important cause of bacillary dysentery in developing countries. Small regulatory RNAs (sRNAs) play essential roles in diverse cellular processes. We found a novel sRNA <italic>Ssr1</italic> based on RT-PCR, northern blot, and 5′RACE in <italic>S. flexneri</italic>. <italic>Ssr1</italic> responds to acidic environmental changes, as shown by a strong linear correlation between the pH value and <italic>Ssr1</italic> expression (<italic>R</italic> = 0.785, <italic>P</italic> &lt; 0.05) using the qRT-PCR method. Deletion of <italic>Ssr1</italic> results in growth retardation at pH values ranging from 5.0 to 7.0 (<italic>P</italic> &lt; 0.05), and the survival rate was reduced by 22% in acidic conditions (pH 3.0). Additionally, virulence was significantly increased in an <italic>Ssr1</italic> mutant strain, as revealed in a murine lung invasion model and survival model assays. By using the sTarPicker method and proteomic analysis, we considered that DnaK, which is a major factor that confers acidic stress tolerance, may be a direct target of <italic>Ssr1</italic>. We also found that <italic>Ssr1</italic> may enhance virulence by directly targeting OmpA; this leads to altered expression of genes in the type three secretion system (T3SS). This work provides new insight into the mechanism of adaptation to environmental stress and into the pathogenesis of <italic>Shigella</italic>.</p>