Stochastic and Differential Activation of σB and PrfA in Listeria monocytogenes at the Single Cell Level under Different Environmental Stress Conditions

Abstract

During host infection, the foodborne pathogen Listeria monocytogenes must sense and respond to rapidly changing environmental conditions. Two transcriptional regulators, the alternative sigma factor B (σB) and the Positive Regulatory Factor A (PrfA), are key contributors to the transcriptomic responses that enable bacterial survival in the host gastrointestinal tract and invasion of host duodenal cells. Increases in temperature and osmolarity induce activity of these proteins; such conditions may be encountered in food matrices as well as within the host gastrointestinal tract. Differences in PrfA and σB activity between individual cells might affect the fate of a cell during host invasion, therefore, we hypothesized that PrfA and σB activities differ among individual cells under heat and salt stress. We used fluorescent reporter fusions to determine the relative proportions of cells with active σB or PrfA following exposure to 45°C heat or 4% NaCl. Activities of both PrfA and σB were induced stochastically, with fluorescence levels ranging from below detection to high among individual cells. The proportion of cells with active PrfA was significantly higher than the proportion with active σB under all tested conditions; under some conditions, nearly all cells had active PrfA. Our findings further support the growing body of evidence illustrating the stochastic nature of bacterial gene expression under conditions that are relevant for host invasion via food-borne, oral infection.

The σB signalling activation pathway in the enteropathogen Clostridioides difficile

“…Heterogeneous σ B activity has also been observed in L. monocytogenes in stressed and non‐stressed cells (Utratna et al, ; Utratna et al, ; Guldimann et al, ). This heterogeneity in σ B activity might lead to a specialized sub‐population resulting in ‘bet‐hedging’ strategy that would maximize the survival chances in adverse environments (Eldar and Elowitz, ; Guldimann et al, ). Interestingly, the existence of specialized sub‐population has been recently reported for toxin gene expression in C. difficile .…”

“…Thus, we assumed the iron-sulphur flavoprotein, CD2684, could contribute to σ B activation in C. difficile. Despite several attempts, we were unable to inactivate CD2684 by allele genetic exchange or ClosTron (Heap et al, 2007;Heap et al, 2010) suggesting that CD2684 could be essential in C. difficile. Thus, using the allele exchange strategy, we integrated the entire P tet element from pRPF185 upstream of the translational initiation codon of CD2684 into the chromosome of both the 630Δerm and the sigB mutant strains (Fig.…”

“…2C) while the expression of sigB under the control of its own promoter led only to a 10-fold overexpression (Table 1). Heterogeneous σ B activity has also been observed in L. monocytogenes in stressed and nonstressed cells (Utratna et al, 2012;Utratna et al, 2014;Guldimann et al, 2017). This heterogeneity in σ B activity might lead to a specialized sub-population resulting in 'bet-hedging' strategy that would maximize the survival chances in adverse environments (Eldar and Elowitz, 2010;Guldimann et al, 2017).…”

Listeria monocytogenes’in RNase III rncS Geninin Silinmesinin Stres Tepkisi, Biyofilm Oluşumu ve Virülansı Üzerine Etkileri

“…It can form biofilms that are resistant to the external environment in animal foods and on the surface of processing containers [3] . Many studies have found that the strong viability and pathogenicity of LM are closely associated to its environmental stress factors and virulence factors [4,5] . To survive in stress conditions, LM has to modulate its transcriptions of related genes constantly to adapt to the different environments.…”

“…To survive in stress conditions, LM has to modulate its transcriptions of related genes constantly to adapt to the different environments. Despite LM possesses many regulatory proteins to modulate gene expression, environmental stress factor Sigma B [4,5] , positive regulatory factor PrfA and response regulator VirR [6,7] appear to play predominant roles in LM survival and infection. In recent years, studies have found that noncoding RNAs (ncRNAs) in LM can form complex regulatory networks with regulatory molecules such as PrfA, Sigma B and VirR, which precisely regulate the virulence and stress response-related genes of LM at transcription, posttranscription, and translational levels [6,8] .…”