Transcriptional and Post-Transcriptional Modulation of SPI1 and SPI2 Expression by ppGpp, RpoS and DksA in Salmonella enterica sv Typhimurium.

Christopher J Rice,Neil Shearer,Arthur Thompson,Vinoy K Ramachandran,Dipshikha Chakravortty

doi:10.1371/journal.pone.0127523

Christopher J Rice, Neil Shearer + Show 3 more

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https://doi.org/10.1371/journal.pone.0127523

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Abstract

The expression of genes within Salmonella Pathogenicity Islands 1 and 2 (SPI1, SPI2) is required to facilitate invasion and intracellular replication respectively of S. Typhimurium in host cell lines. Control of their expression is complex and occurs via a variety of factors operating at transcriptional and post-transcriptional levels in response to the environmental stimuli found within the host. Several of the factors that modulate SPI1 and SPI2 expression are involved in the redistribution or modification of RNA polymerase (RNAP) specificity. These factors include the bacterial alarmone, ppGpp, the alternative sigma factor, RpoS, and the RNAP accessory protein, DksA. In this report we show not only how these three factors modulate SPI1 and SPI2 expression but also how they contribute to the ‘phased’ expression of SPI1 and SPI2 during progress through late-log and stationary phase in aerobic rich broth culture conditions. In addition, we demonstrate that the expression of at least one SPI1-encoded protein, SipC is subject to DksA-dependent post-transcriptional control.

Highlights

Pathogenic serovars of Salmonella infect both humans and animals, causing in humans either a self-limited gastroenteritis
In this study we show that RpoS, DksA and ppGpp play both antagonistic and complementary roles resulting in the modulation of Salmonella Pathogenicity Island 1 (SPI1) and SPI2 transcription during late-log and stationary phase growth in aerobic LB broth cultures
Whereas the absence of ppGpp resulted in decreased SPI1 encoded gene transcript levels at late log phase (LLP), early stationary phase (ESP), MSP and to a lesser extent at LSP (Fig 1B), in the ΔrpoS and ΔdksA strains, the transcript levels of most SPI1 encoded genes were increased at MSP and LSP (Fig 1B and 1C)

Summary

Introduction

Pathogenic serovars of Salmonella infect both humans and animals, causing in humans either a self-limited gastroenteritis Salmonella is the second most reported zoonotic infection in humans and the most frequent cause of food borne outbreaks in the EU [1]. Salmonella invades epithelial cells lining the small intestine, mediated by Salmonella Pathogenicity Island 1 (SPI1), encoding a type 3 secretion system (T3SS). SPI1 triggers the injection of effector proteins into the host cell to facilitate uptake of bacteria during the process of invasion. Intracellular Salmonella employ a second T3SS encoded within SPI2, which modifies the initial membrane-bound compartment or phagosome to form the ‘Salmonella containing vacuole’ (SCV) [2]. The SCV avoids fusion with lysosomes, enabling Salmonella to evade the PLOS ONE | DOI:10.1371/journal.pone.0127523. The SCV avoids fusion with lysosomes, enabling Salmonella to evade the PLOS ONE | DOI:10.1371/journal.pone.0127523 June 3, 2015

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