H-NS is the major repressor of Salmonella Typhimurium Pef fimbriae expression

Abstract

Fimbriae play an important role in adhesion and are therefore essential for the interaction of bacteria with the environments they encounter. Most of them are expressed in vivo but not in vitro, thus making difficult the full characterization of these fimbriae. Here, we characterized the silencing of plasmid-encoded fimbriae (Pef) expression, encoded by the pef operon, in the worldwide pathogen Salmonella Typhimurium. We demonstrated that the nucleoid-associated proteins H-NS and Hha, and their respective paralogs StpA and YdgT, negatively regulate at pH 5.1 and pH 7.1 the transcription of the pef operon. Two promoters, PpefB and PpefA, direct the transcription of this operon. All the nucleoid-associated proteins silence the PpefB promoter and H-NS also targets the PpefA promoter. While Hha and YdgT are mainly considered as acting primarily through H-NS to modulate gene transcription, our results strongly suggest that Hha and YdgT silence pef transcription at acidic pH either by interacting with StpA or independently of H-NS and StpA. We also confirmed the previously described post-transcriptional repression of Pef fimbriae by CsrA titration via the fim mRNA and CsrB and CsrC sRNA. Finally, among all these regulators, H-NS clearly appeared as the major repressor of Pef expression. These results open new avenues of research to better characterize the regulation of these bacterial adhesive proteins and to clarify their role in the virulence of pathogens.

Pre-Growth Culture Conditions Affect Type 1 Fimbriae-Dependent Adhesion of Salmonella

“…From those, Pef is reported to be expressed in static conditions and an acidic medium [36]. T1F expression has been reported to prevent the expression of Pef [37]; therefore, a lack of T1F may induce Pef expression.…”

Transcriptional Regulation of the Multiple Resistance Mechanisms in Salmonella—A Review

“…To identify foreign genes, the H-NS system recognizes a prokaryotic AT-hook DNA binding motif, which is preferentially inserted into DNA sequences rich in AT pairs [152]. Thus, these proteins bind the newly acquired sequence and prevent the potentially harmful effects of their uncontrolled expression [151,153]. In macrophages, S. enterica degrades H-NS allowing the expression of HGT.…”

“…Conservation in amino acid sequences of both the Lon protease and in the H-NS itself suggests that gut microflora have a shared, discovered strategy of expression of alien genes suppressed by H-NS. The H-NS is protected before Lon when it is bound to DNA [ 153 ].…”

Recent Advances in Our Understanding of the Diversity and Roles of Chaperone-Usher Fimbriae in Facilitating Salmonella Host and Tissue Tropism

“…was associated with preferential binding to cell lines representing the host that the serovar was isolated from (e.g., Dublin and bovine cells) ( Yue et al, 2015 ), corroborating the results of previous studies that suggested that different fimH alleles allowed for selective binding to different host cell types ( Boddicker et al, 2002 ; Kisiela et al, 2012 ; Grzymajło et al, 2013 ). Last, fimbrial gene expression is a complex process that involves regulators encoded in the fimbrial gene cluster that directly regulate transcription of genes in the cluster ( Kolenda et al, 2019 ), as well as global regulators including H-NS ( Hurtado-Escobar et al, 2019 ), CsrA ( Sterzenbach et al, 2013 ), and HdfR ( García-Pastor et al, 2019 ). These complex regulatory pathways may also partially explain why strains representing different serovars show variable expression of fimbriae, and why deletion of these chaperone-usher fimbrial gene clusters in has varying effects on influencing virulence ( Azriel et al, 2017 ).…”