crosstalk between virulence loci regulation of salmonella enterica pathogenicity island 1 (spi-1) by products of the std fimbrial operon毒性基因座调控之间的串扰沙门氏菌致病性岛1(spi-1)性病fimbrial操纵子的产品.pdf

Crosstalk between Virulence Loci: Regulation of Salmonella enterica Pathogenicity Island 1 (SPI-1) by Products of the std Fimbrial Operon ´ ´ Javier Lopez-Garrido, Josep Casadesus* ´ Departamento de Genetica, Universidad de Sevilla, Sevilla, Spain Abstract Invasion of intestinal epithelial cells is a critical step in Salmonella infection and requires the expression of genes located in Salmonella pathogenicity island 1 (SPI-1). A key factor for SPI-1 expression is DNA adenine (Dam) methylation, which activates synthesis of the SPI-1 transcriptional activator HilD. Dam-dependent regulation of hilD is postranscriptional (and therefore indirect), indicating the involvement of unknown cell functions under Dam methylation control. A genetic screen has identified the std fimbrial operon as the missing link between Dam methylation and SPI-1. We show that all genes in the std operon are part of a single transcriptional unit, and describe three previously uncharacterized ORFs (renamed stdD, stdE, and stdF). We present evidence that two such loci (stdE and stdF) are involved in Dam-dependent control of Salmonella SPI- 1: in a Dam2 background, deletion of stdE or stdF suppresses SPI-1 repression; in a Dam+ background, constitutive expression of StdE and/or StdF represses SPI-1. Repression of SPI-1 by products of std operon explains the invasion defect of Salmonella Dam2 mutants, which constitutively express the std operon. Dam-dependent repression of std in the ileum may be required to permit invasion, as indicated by two observations: constitutive expression of StdE and StdF reduces invasion of epithelial cells in vitro (1,000 fold) and attenuates Salmonella virulence in the mouse model (.60 fold). In turn, crosstalk between std and SPI-1 may