AUTHOR=Lin Zhiwei , Cai Xia , Chen Mingliang , Ye Lina , Wu Yang , Wang Xiaofei , Lv Zhihui , Shang Yongpeng , Qu Di 

TITLE=Virulence and Stress Responses of Shigella flexneri Regulated by PhoP/PhoQ

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02689

DOI=10.3389/fmicb.2017.02689

ISSN=1664-302X

ABSTRACT=<p>The two-component signal transduction system PhoP/PhoQ is an important regulator for stress responses and virulence in most Gram-negative bacteria, but characterization of PhoP/PhoQ in <italic>Shigella</italic> has not been thoroughly investigated. In the present study, we found that deletion of <italic>phoPQ</italic> (Δ<italic>phoPQ</italic>) from <italic>Shigella flexneri</italic> 2a 301 (<italic>Sf</italic>301) resulted in a significant decline (reduced by more than 15-fold) in invasion of HeLa cells and Caco-2 cells, and less inflammation (− or +) compared to <italic>Sf</italic>301 (+++) in the guinea pig Sereny test. In low Mg<sup>2+</sup> (10 μM) medium or pH 5 medium, the Δ<italic>phoPQ</italic> strain exhibited a growth deficiency compared to <italic>Sf</italic>301. The Δ<italic>phoPQ</italic> strain was more sensitive than <italic>Sf</italic>301 to polymyxin B, an important antimicrobial agent for treating multi-resistant Gram-negative infections. By comparing the transcriptional profiles of Δ<italic>phoPQ</italic> and <italic>Sf</italic>301 using DNA microarrays, 117 differentially expressed genes (DEGs) were identified, which were involved in Mg<sup>2+</sup> transport, lipopolysaccharide modification, acid resistance, bacterial virulence, respiratory, and energy metabolism. Based on the reported PhoP box motif [(T/G) GTTTA-5nt-(T/G) GTTTA], we screened 38 suspected PhoP target operons in <italic>S. flexneri</italic>, and 11 of them (<italic>phoPQ, mgtA, slyB, yoaE, yrbL, icsA, yhiWX, rstA, hdeAB, pagP</italic>, and <italic>shf</italic>–<italic>rfbU</italic>-<italic>virK</italic>-<italic>msbB2</italic>) were demonstrated to be PhoP-regulated genes based on electrophoretic mobility shift assays and β-galactosidase assays. One of these PhoP-regulated genes, <italic>icsA</italic>, is a well-known virulence factor in <italic>S. flexneri</italic>. In conclusion, our data suggest that the PhoP/PhoQ system modulates <italic>S. flexneri</italic> virulence (in an <italic>icsA</italic>-dependent manner) and stress responses of Mg<sup>2+</sup>, pH and antibacterial peptides.</p>