The Salmonella typhimurium virulence plasmid encodes a positive regulator of a plasmid-encoded virulence gene

Abstract

The 90-kb virulence plasmid of SalmoneUa typhimurium is necessary for invasion beyond the Peyer's patches to the mesenteric lymph nodes and spleens of orally inoculated mice. Two TnS insertions located on the left side of a previously identified 14-kb virulence region (P. A. Gulig and R. Curtiss m, Infect. Immun. 58:3262-3271, 1988) and mapping 272 bp from each other exhibited opposite effects on splenic infection of mice after oral inoculation. spvR23::TnS decreased splenic infection by 1,000-fold, whereas a spv-14::TnS mutant outcompeted wild-type S. typhimurium for splenic infection by 27-fold in mice fed mixtures of mutated and wild-type S. typhimurium. spvR23::Tn5 was complemented by a virulence plasmid subclone with an insert sequence encoding only an 891-bp open reading frame specifying a 33,000-molecular-weight protein. The amino acid sequence of this open reading frame had significant homology to members of the LysR family of positive regulatory proteins; thus, the gene was named spvR (salmonella plasmid virulence). To examine the possible regulatory effects of spvR on other virulence genes, we constructed a lacZ operon fusion in a downstream virulence gene, spvB. When spvR subcloned behind the lac promoter was provided on a separate plasmid in trans to the spvB-lacZ operon fusion, transcription of spvB increased 15-fold. spv-14::TnS, whih conferred a competitive advantage to S. typhimurium, increased the expression of a spvR-lacZ operon fusion in cis. spvR is therefore a positive regulator of spvB and an essential virulence gene of S. typhimurium. As opposed to having spvR subeloned behind the lac promoter, the wild-type spvR gene present on the virulence plasmid did not function to positively regulate spvB-lacZ in trans when salmonellae were grown to the log phase in L broth, suggesting that this regulatory system is activated in vivo during infection.Related high-molecular-weight plasmids of several serotypes and species of invasive salmonellae encode essential virulence functions (reviewed in reference 15). The 90-kb virulence plasmid of Salmonella typhimurium is responsible for invasion of salmonellae beyond the Peyer's patches of the small intestine to the mesenteric lymph nodes and spleens of mice after oral inoculation (18,40). The specific function(s) that the virulence plasmid confers to S. typhimurium to enable invasive infection has not been determined (15), although it has been suggested that the virulence plasmid may be involved in immunosuppression (23). Several groups have alluded to functions related to intracellular infection or macrophage resistance as being associated with the virulence plasmid; however, no direct proof has been published (15,18).The large size of the 90-kb virulence plasmid of S. typhimurium made it desirable to identify smaller specific regions of the plasmid that were involved in conferring virulence. Gulig and Curtiss used in vivo selection of virulence-conferring clones of the virulence plasmid to identify sequences associated with virulence in mice (19). S. t...

Regulation of plasmid virulence gene expression in Salmonella dublin involves an unusual operon structure

“…The loss of virulence after spvR mutation by transposon insertions has been repeatedly demonstrated (2,4,34). Taken together, these results suggest that SpvR mediates a coordinate regulation of the plasmid virulence genes in the course of infection that allows the microorganisms to respond to a specific hostile environment beyond the Peyer's patches in mesenteric lymph nodes, liver, and spleen.…”

“…Amino acid homology and recent published data suggested that spvR encodes a protein with a transcriptional activator function (4,8,25,40). To establish spvR-dependent regulation of spvA, spvB, spvC, and spvD, we analyzed their transcription with and without the presence of SpvR by comparing pSDL2 and pSD15-2.…”

IS200 fingerprint of Salmonella enterica serotype Typhimurium human strains isolated in Sardinia

“…All the strains that harboured a 100 kb plasmid, amplified a band of 890 bp (Table 2), with the exception of strain 68, corresponding to the spvR gene of the control sample, plasmid pGTR061, that carries the spv region [23].…”

Regulation of the spvR gene of the Salmonella typhimurium virulence plasmid during exponential-phase growth in intracellular salts medium and at stationary phase in L broth

“…The spv genes increase the growth rate of the salmonellae within host cells (Gulig & Doyle, 1993), specifically macrophages (Gulig et al, 1998). However, the exact mechanism(s) by which the spu genes increase the growth rate within host cells is not known, The spv genes consist of spuABCD, which are transcribed as an operon and spvR, which encodes the positive regulatory protein for the spv genes (Caldwell & Gulig, 1991;Matsui et al, 1991;Taira et al, 1991). SpvR is a member of the LysR family of positive activators and regulates the transcription of the spv genes by binding to sequences upstream of spvA and SPUR (Grob & Guiney, 1996;Grob et al, 1997).…”