OmpR Regulates the Two-Component System SsrA-SsrB in Salmonella Pathogenicity Island 2

Abstract

Salmonella pathogenicity island 2 (SPI-2) encodes a putative, two-component regulatory system, SsrA-SsrB, which regulates a type III secretion system needed for replication inside macrophages and systemic infection in mice. The sensor and regulator homologs, ssrAB (spiR), and genes within the secretion system, including the structural gene ssaH, are transcribed after Salmonella enters host cells. We have studied the transcriptional regulation of ssrAB and the secretion system by using gfp fusions to the ssrA and ssaH promoters. We found that early transcription of ssrA, after entry into macrophages, is most efficient in the presence of OmpR. An ompR mutant strain does not exhibit replication within cultured macrophages. Furthermore, footprint analysis shows that purified OmpR protein binds directly to the ssrA promoter region. We also show that minimal medium, pH 4.5, induces SPI-2 gene expression in wild-type but not ompR mutant strains. We conclude that the type III secretion system of SPI-2 is regulated by OmpR, which activates expression of ssrA soon after Salmonella enters the macrophage.

Comparison of live and inactivated Salmonella Typhimurium vaccines containing different combinations of SPI-1 and SPI-2 antigens in poultry

“…SPI-2 genes are, on the other hand, expressed at a high level in the stationary phase of growth when the availability of nutrients become limiting. This is consistent with the intracellular conditions encountered by S. Typhimurium (Deiwick et al, 1999;Lee et al, 2000). Since SPI-1 and SPI-2 encoded proteins are expressed in vivo, these proteins may represent important antigens for the immune system of a host.…”

Differential interaction of Salmonella enterica serovars with lettuce cultivars and plant-microbe factors influencing the colonization efficiency

“…The genes related to a sugar-like carbon source were OtsA (trehalose-6-phosphate synthase), which utilizes glucose-6-phosphate as substrate (Gizver et al, 1988), UhpC (hexose phosphate utilization protein), which is a sensor for external glucose-6-phosphate) (Schwjppe et al, 2003), MetE (methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase), a vitamin B 12 -independent enzyme (Urbanowski and Stauffer, 1989), DsrA (putative anti-silencer RNA), a regulator of transcription to express RcsA promoter, which in its turn is responsible for capsular polysaccharide synthesis (Sledjeski and Gottesman, 1995), RseA (sigma-E factor regulatory protein), which is involved in the storage of sigma which is released during stress (Ades et al, 1999), SsaH and SsaM (putative effector proteins), both regulators of secretion of the type III secretion system (Lee et al, 2000) and SpaO, involved in surface presentation of antigens, secretory proteins. Other genes that were differentially expressed were related to specific limiting factors like iron (gene SitD) or anaerobic respiration (TtrA).…”

FliC-Specific CD4+ T Cell Responses Are Restricted by Bacterial Regulation of Antigen Expression

“…SPI1 genes are required for invasion by extracellular bacteria (12), and SPI2 genes encode one set of gene products required for intracellular replication and systemic infection (13). SPI1 and SPI2 genes are regulated in response to a variety of environmental signals including, but not limited to osmolarity (14 -16), pH (14,15,17), Mg 2ϩ depletion (7), oxygen tension (14), phosphate starvation (18), bile (19), cationic microbial peptides (20), and intestinal short-chain fatty acids (21). In fact, it has been estimated that ϳ20% of all Salmonella coding sequences, including those required for metabolism, ion transport, resistance to antimicrobial peptides, and motility, are differentially regulated by Salmonella during growth in macrophages (22).…”