The YfgL Lipoprotein Is Essential for Type III Secretion System Expression and Virulence of Salmonella enterica Serovar Enteritidis

Abstract

Salmonella enterica, like many gram-negative pathogens, uses type three secretion systems (TTSS) to infect its hosts. The three TTSS of Salmonella, namely, TTSS-1, TTSS-2, and flagella, play a major role in the virulence of this bacterium, allowing it to cross the intestinal barrier and to disseminate systemically. Previous data from our laboratory have demonstrated the involvement of the chromosomal region harboring the yfgL, engA, and yfgJ open reading frames in S. enterica serovar Enteritidis virulence. Using microarray analysis and real-time reverse transcription-PCR after growth of bacterial cultures favorable for either TTSS-1 or TTSS-2 expression, we show in this study that the deletion in S. enterica serovar Enteritidis of yfgL, encoding an outer membrane lipoprotein, led to the transcriptional down-regulation of most Salmonella pathogenicity island 1 (SPI-1), SPI-2, and flagellar genes encoding the TTSS structural proteins and effector proteins secreted by these TTSS. In line with these results, the virulence of the ⌬yfgL mutant was greatly attenuated in mice. Moreover, even if YfgL is involved in the assembly of outer membrane proteins, the regulation of TTSS expression observed was not due to an inability of the ⌬yfgL mutant to assemble TTSS in its membrane. Indeed, when we forced the transcription of SPI-1 genes by constitutively expressing HilA, the secretion of the TTSS-1 effector protein SipA was restored in the culture supernatant of the mutant. These results highlight the crucial role of the outer membrane lipoprotein YfgL in the expression of all Salmonella TTSS and, thus, in the virulence of Salmonella. Therefore, this outer membrane protein seems to be a privileged target for fighting Salmonella.Salmonella enterica infections are an important worldwide health problem. Salmonella serovars are responsible for diseases ranging from mild gastroenteritis to life-threatening systemic infections. During the course of infection, these serovars use many virulence factors, among which the type III secretion systems (TTSS) play a major role. TTSS-1, encoded by Salmonella pathogenicity island 1 (SPI-1), mainly allows intestinal epithelial cell invasion (57), thereby allowing the bacteria to cross the intestinal barrier. TTSS-2, encoded by SPI-2, is required for intracellular survival and multiplication (54) and, consequently, is important for systemic dissemination of the bacteria. The virulence phenotypes associated with SPI-1 and SPI-2 are dependent on the ability of the TTSS to deliver effector proteins into the host cell cytosol. Thus, bacteria hijack the eukaryotic cellular machinery for their own profit. The flagella, which share a common architectural design with TTSS, are involved in the motility of the bacteria and favor the interaction with the intestinal epithelium (31, 47). However, their role in Salmonella virulence remains controversial (26,27,47).We previously characterized a Salmonella enterica subsp. enterica serovar Enteritidis mutant which was altered in motility and in invasion of Cac...

TheKlebsiella pneumoniaeYfgL (BamB) lipoprotein contributes to outer membrane protein biogenesis, type-1 fimbriae expression, anti-phagocytosis, andin vivovirulence

“…26,27 , 34 In S. enterica serovar Enteritidis, the yfgL mutant had reduced invasivity for enterocytes compared to the wild-type strain. 34 Similarly, deletion of the yfgL gene in an adherent-invasive E. coli strain LF82 resulted in a decreased invasivity for intestinal epithelial cells.…”

“…22,24,25 YfgL (BamB) is an OM lipoprotein, which is anchored to the periplasmic face of the OM 22 and displays a role in membrane permeability and antibiotic resistance of E. coli and S. enterica serovar Enteritidis. 26,27 A previous study demonstrated that the Salmonella YfgL lipoprotein is essential for expression of the type-III secretion system. 27 Several putative secretion systems, but not a type-III secretion system, have already been identified in the K. pneumoniae NTUH-K2044 genome.…”

“…26,27 A previous study demonstrated that the Salmonella YfgL lipoprotein is essential for expression of the type-III secretion system. 27 Several putative secretion systems, but not a type-III secretion system, have already been identified in the K. pneumoniae NTUH-K2044 genome. 28 Additionally, some OM proteins contribute significantly to the virulence of K. pneumoniae, by conferring protection against host's innate immunity.…”

Cell invasion of poultry-associated Salmonella enterica serovar Enteritidis isolates is associated with pathogenicity, motility and proteins secreted by the type III secretion system

“…Mutations in the genes encoding secretory effector proteins or genes that regulate their expression lead to virulence attenuation in S. Enteritidis (Amy et al, 2004;Fardini et al, 2007;Parker & GuardPetter, 2001). At least two low invasive isolates, C19 and C45, tested here showed impaired secretion of SipA and SipD proteins (Fig.…”

Rck of Salmonella enterica, subspecies enterica serovar Enteritidis, mediates Zipper-like internalization

“…GFP-Cdc42 was generated by subcloning wild-type Cdc42 from pRK5-myc Cdc42 into pEGFP-C2 (CLONTECH Laboratories Inc; BamHI and EcoRI restriction sites). The rck mutant of LA5 strain was obtained using the lambda-Red mutagenesis system, modified as previously described [43,44]. The sequences of P1 and P2 primers used for this strain construction are listed in Table 3.…”