Global gene expression of a murein (Braun) lipoprotein mutant of Salmonella enterica serovar Typhimurium by microarray analysis A.A. Fadl a , C.L. Galindo a , J. Sha a , G.R. Klimpel a , V.L. Popov b , A.K. Chopra a, ⁎ a Department of Microbiology and Immunology, 301 University Blvd, University of Texas Medical Branch, Galveston, Texas 77555-1070, United States b Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-1070, United States Received 12 October 2005; received in revised form 23 January 2006; accepted 25 January 2006 Available online 29 March 2006 Received by D.L. Court Abstract Braun/murein lipoprotein (Lpp) is one of the major outer membrane components of gram-negative enteric bacteria involved in inflammatory responses and septic shock. In previous studies, we reported that two copies of the lipoprotein (lpp) gene (designated as lppA and lppB) existed on the chromosome of Salmonella enterica serovar Typhimurium. Deletion of both lppA and lppB genes rendered Salmonella defective in invasion, motility, induction of cytotoxicity, and production of inflammatory cytokines/chemokines. The lppAB double-knockout (DKO) mutant was attenuated in mice, and animals immunized with this mutant were protected against subsequent challenge with lethal doses of wild-type (wt) S. Typhimurium. To better understand how deletion of the lpp gene might affect Salmonella virulence, we performed global transcriptional profiling of the genes in the wt and the lppAB DKO mutant of S. Typhimurium using microarrays. Our data revealed alterations in the expression of flagellar genes, invasion-associated type III secretion system genes, and transcriptional virulence gene regulators in the lppAB DKO mutant compared to wt S. Typhimurium. These data correlated with the lppAB DKO mutant phenotype and provided possible mechanism(s) of Lpp-associated attenuation in S. Typhimurium. Although these studies were performed in in vitro grown bacteria, our future research will be targeted at global transcriptional profiling of the genes in in vivo grown wt S. Typhimurium and its Lpp mutant. © 2006 Elsevier B.V. All rights reserved. Keywords: DNA microarrays; Virulence genes; Bacterial attenuation 1. Introduction Salmonella enterica serovar Typhimurium is an invasive bacterium that causes gastroenteritis and septicemia due to the consumption of contaminated food (Mishu et al., 1994). S. Typhimurium colonizes intestinal mucosa, with fecal shedding of the organisms providing a source of infection for other animals and humans (Barrow et al., 1988; Wallis and Galyov, 2000). Subsequent to colonization, salmonellae transcytose M cells and intestinal epithelial cells and are phagocytized by resident macrophages, where they multiply and further invade internal organs, such as the liver and spleen (Collins and Carter, 1974; Hsu, 1989; Mastroeni et al., 1995). S. Typhimurium invasion of epithelial cells is mediated by translocation of pathogenicity island-1 (SPI-1) effector proteins into the cytosol of host cells (Hayward et al., 2002). The effector proteins activate signal transduction pathways that lead to actin polymerization and cell membrane ruffling, resulting in the uptake of bacteria in membrane-bound vesicles (Finlay et al., 1991; Garcia-del Portillo and Finlay, 1994; Zhou and Galan, 2001; Cardenas et al., 2004). One of the most serious complications of S. Typhimurium infection is septic shock, which is mediated by lipopolysaccha- ride (LPS) (Morrison and Ryan, 1987; Glauser et al., 1991). Recently, we reported that Braun/murein lipoprotein (Lpp), one of the most abundant components of the outer membrane of gram-negative bacteria of the family enterobacteriaceae (Braun and Hantke, 1974), contributed significantly to septic shock development by inducing production of tumor necrosis factor- alpha (TNF-α) and interleukin (IL)-6 in primary macrophages Gene 374 (2006) 121 – 127 www.elsevier.com/locate/gene Abbreviations: Lpp, lipoprotein; lpp, lipoprotein gene; lppAB DKO, lppA and lppB double-knockout isogenic mutants; wt, wild type; SPI-1, Salmonella pathogenicity island-1; TTSS, type III secretion system; IL-6, interleukin-6; TNF-α, tumor necrosis factor alpha; TLR, toll-like receptor. ⁎ Corresponding author. Tel.: +1 409 747 0578; fax: +1 409 747 6869. E-mail address: achopra@utmb.edu (A.K. Chopra). 0378-1119/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gene.2006.01.034