Transcriptional Regulation of the Type VI Secretion System 1 Genes by Quorum Sensing and ToxR in Vibrio parahaemolyticus

Abstract

Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis, harbors two separate T6SSs on chromosomes 1 and 2, i.e., T6SS1 (VP1386-1420) and T6SS2 (VPA1025-1046). T6SS1 contains at least 7 putative operons: VP1386-1387, VP1388-1390, VP1392-1391, VP1393-1406, VP1400-1406, VP1409-1407, and VP1410-1420. V. parahaemolyticus AphA and OpaR are the two master regulators of quorum sensing (QS) system that are highly expressed at low cell density and high cell density, respectively. ToxR is a membrane-bound virulence regulatory protein conserved across the Vibrio family. In the present work, we show that ToxR coordinates with AphA and OpaR to repress T6SS1 expression in V. parahaemolyticus. OpaR binds to the promoters of VP1388-1390, VP1400-1406, and VP1409-1407 to repress their transcription, but it appears to negatively regulate VP1393-1406 transcription in an indirect manner. By contrast, AphA negatively regulated the above four T6SS1 operons in an indirect manner. In addition, ToxR binds to the promoters of VP1400-1406 and VP1409-1407 to inhibit their transcription, but it presents an indirect interaction with VP1388-1390 and VP1393-1406 promoters. Notably, the expression of ToxR also manifested in a QS-dependent manner and the highest expression occurred at LCD. Meanwhile, the highest expression of T6SS1 occurred at an OD600 value of 0.6 to 0.8 due to the tight regulation of ToxR and QS, suggesting T6SS1 functions only during the mid-logarithmic growth phase. These observations provide significant insight into the molecular mechanism of T6SS1 gene regulation by QS and ToxR in V. parahaemolyticus.

QsvR integrates into quorum sensing circuit to control Vibrio parahaemolyticus virulence

“…In V. parahaemolyticus , AphA activates the mouse lethality, cytotoxicity and hemolytic activity (Wang et al ., ), while OpaR regulates approximately 5.2% of the total number of genes (Gode‐Potratz and McCarter, ). AphA and OpaR coordinately regulate the T6SS (T6SS1 and T6SS2) (Wang et al ., ; Zhang et al ., ), T3SS1 and Vp‐PAI genes (present study). Therefore, the coordinated regulation of virulence genes by AphA and/or OpaR orthologs and/or other regulatory factors appears to be a universal mechanism in Vibrio species during QS signal transduction.…”

The regulatory network of Vibrio parahaemolyticus type VI secretion system 1

“…activation. In support of this model, OpaR was previously suggested to directly bind to promoter regions of V. parahaemolyticus T6SS1 operons, including the promoter of the operon encoding the positive downstream regulator, VP1407 (Zhang et al, 2017).…”

“…This result also implies the existence of a quorum‐sensing dependent, surface sensing/TfoY‐independent pathway for T6SS1 activation. In support of this model, OpaR was previously suggested to directly bind to promoter regions of V. parahaemolyticus T6SS1 operons, including the promoter of the operon encoding the positive downstream regulator, VP1407 (Zhang et al ., ).…”

“…Note that a previous study also implicated ToxR and AphA in the regulation of V. parahaemolyticus T6SS1 (Zhang et al ., ); however, we did not include them in our epistasis analyses because we could not detect any effect of these regulators on T6SS1 activity in our previous work (i.e. their deletion had no negative effect on T6SS1‐mediated secretion or antibacterial activity) (Salomon, Klimko, et al ., ).…”

Does quorum sensing interference affect the fitness of bacterial pathogens in the real world?

“…Translocation of toxic effectors to neighbouring cells through the type VI secretion system thus confers a significant fitness advantage to pathogenic bacteria by facilitating invasion of (host associated) microbial communities, thereby increasing host colonization and transmission to new hosts (Zhao et al ., ). Importantly, in several pathogens (e.g., Burkholderia thailandensis , Vibrio alginolyticus , V. cholerae , Vibrio parahaemolyticus and Yersinia pseudotuberculosis ), the type VI secretion system is under quorum sensing control (Zheng et al ., ; Zhang et al ., ; ; Majerczyk et al ., ; Yang et al ., ).…”