AUTHOR=Guo Rui Hong , Lim Ju Young , Tra My Duong Nu , Jo Se Jin , Park Jung Up , Rhee Joon Haeng , Kim Young Ran 

TITLE=Vibrio vulnificus RtxA1 Toxin Expression Upon Contact With Host Cells Is RpoS-Dependent

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2018.00070

DOI=10.3389/fcimb.2018.00070

ISSN=2235-2988

ABSTRACT=<p>The expression of virulence genes in bacteria is known to be regulated by various environmental and host factors. <italic>Vibrio vulnificus</italic>, an estuarine bacterium, experiences a dramatic environmental change during its infection process. We reported that <italic>V. vulnificus</italic> 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 <italic>V. vulnificus</italic> cytotoxicity and mouse lethality. The growth of <italic>rpoS</italic> mutant strain was comparable to that of wild-type in heart infusion (HI) media and DMEM with HeLa cell lysate. An <italic>rpoS</italic> mutation resulted in decreased cytotoxicity, which was restored by <italic>in trans</italic> complementation. Interestingly, host contact increased the expression and secretion of <italic>V. vulnificus</italic> RtxA1 toxin, which was decreased and delayed by the <italic>rpoS</italic> mutation. Transcription of the cytotoxic gene <italic>rtxA1</italic> and its transporter <italic>rtxB1</italic> was significantly increased after host factor contact, whereas the activity was decreased by the <italic>rpoS</italic> mutation. In contrast, the <italic>rpoS</italic> mutation showed no effect on the transcriptional activity of a cytolytic heamolysin gene (<italic>vvhA</italic>). Additionally, the LD<sub>50</sub> of the <italic>rpoS</italic> 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 <italic>V. vulnificus</italic> RtxA1 toxin and its transporter upon host contact.</p>