Single Cell Analysis of Bistable Expression of Pathogenicity Island 1 and the Flagellar Regulon in Salmonella enterica.

María Antonia Sánchez-Romero,Josep Casadesús

doi:10.3390/microorganisms9020210

Abstract

Bistable expression of the Salmonella enterica pathogenicity island 1 (SPI-1) and the flagellar network (Flag) has been described previously. In this study, simultaneous monitoring of OFF and ON states in SPI-1 and in the flagellar regulon reveals independent switching, with concomitant formation of four subpopulations: SPI-1OFF FlagOFF, SPI-1OFF FlagON, SPI-1ON FlagOFF, and SPI-1ON FlagON. Invasion assays upon cell sorting show that none of the four subpopulations is highly invasive, thus raising the possibility that FlagOFF cells might contribute to optimal invasion as previously proposed for SPI-1OFF cells. Time lapse microscopy observation indicates that expression of the flagellar regulon contributes to the growth impairment previously described in SPI-1ON cells. As a consequence, growth resumption in SPI-1ON FlagON cells requires switching to both SPI-1OFF and FlagOFF states.

Highlights

Island 1 and the Flagellar Regulon in Invasion of epithelial cells by Salmonella enterica requires the activity of effectors secreted through the type III secretion system (T3SS) of pathogenicity island 1 (SPI-1)
We show that expression of the flagellar regulon contributes to the growth impairment of SPI-1ON cells
The resulting strain (SV8533, sipB::gfp fliC::mCherry) was used to monitor the pattern of SPI-1 and flagellar expression using fluorescence microscopy and flow cytometry in cultures grown in invasive conditions (LB under oxygen limitation)

Summary

Introduction

Island 1 and the Flagellar Regulon in Invasion of epithelial cells by Salmonella enterica requires the activity of effectors secreted through the type III secretion system (T3SS) of pathogenicity island 1 (SPI-1). The mechanism that controls SPI-1 bistability remains unknown but probably depends on complex interactive networks and feedback loops involving SPI-1 regulators [4]. Some such regulators control crosstalk between SPI-1 and other gene networks, and an example is the flagellar regulon [4,5,6]. Growth retardation associated to SPI-1 expression confers increased antibiotic resistance to SPI-1ON cells [8]

Methods

Results

Discussion

Conclusion