Abstract
Listeria monocytogenes has evolved an extensive array of mechanisms for coping with stress and adapting to changing environmental conditions, ensuring its virulence phenotype expression. For this reason, L. monocytogenes has been identified as a significant food safety and public health concern. Among these adaptation systems are cold shock proteins (Csps), which facilitate rapid response to stress exposure. L. monocytogenes has three highly conserved csp genes, namely, cspA, cspB, and cspD. Using a series of csp deletion mutants, it has been shown that L. monocytogenes Csps are important for biofilm formation, motility, cold, osmotic, desiccation, and oxidative stress tolerance. Moreover, they are involved in overall virulence by impacting the expression of virulence-associated phenotypes, such as hemolysis and cell invasion. It is postulated that during stress exposure, Csps function to counteract harmful effects of stress, thereby preserving cell functions, such as DNA replication, transcription and translation, ensuring survival and growth of the cell. Interestingly, it seems that Csps might suppress tolerance to some stresses as their removal resulted in increased tolerance to stresses, such as desiccation for some strains. Differences in csp roles among strains from different genetic backgrounds are apparent for desiccation tolerance and biofilm production. Additionally, hierarchical trends for the different Csps and functional redundancies were observed on their influences on stress tolerance and virulence. Overall current data suggest that Csps have a wider role in bacteria physiology than previously assumed.
Highlights
This review focuses on knowledge of cold shock proteins (Csps)-family proteins functions, with emphasis on what is currently known about their role in stress response and virulence in L. monocytogenes
Csps seem to be crucial in maintaining cell invasiveness post-cold exposure, a situation most L. monocytogenes strains might encounter in foods before entering the host
Zhang et al proposed the presence of an autoregulatory switch that allows Csps to remodel their own 5’ untranslated leader regions (5’ UTR), fine-tuning their own expression based on cellular needs enabling dynamic regulation of overall translation [32]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Csps are RNA- and DNA-binding proteins used in bacteria for regulating expression of numerous genes, including those relevant in virulence and stress responses [25,26,27,28,29,30]. This Csp structure is highly conserved among different organisms including bacteria (reviewed by [31,44,45]) In terms of their molecular functional mechanisms, one of the major functions postulated for Csps is that they act as RNA chaperones minimizing or melting mRNA secondary structures, thereby facilitating initiation and progression of protein translation under adverse conditions, such as low temperatures. We review the roles of Csps in these processes or against these stressors as well as Csps contributions to virulence (Figure 2)
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