B. melitensis 16M genome analysis revealed the presence of six putative sigma factor-encoding genes: rpoD, rpoH1, rpoH2, rpoE1, rpoE2, and rpoN. We mutated all these genes except rpoD. Phenotypic analysis of the mutants reveals that a strain carrying an rpoH2 null mutation (⌬rpoH2) is impaired for growth at 21 and 42°C and shows increased sensitivity to hydrogen peroxide. Compared to the wild-type strain, the ⌬rpoH2 mutant is attenuated in all virulence models tested. Three other null mutants (⌬rpoH1, ⌬rpoE1, and ⌬rpoE2 mutants) are also defective for survival in mice at 4 weeks postinfection. We also demonstrated that rpoH2 deletion strongly reduces the expression of two major virulence factors in B. melitensis, the type IV secretion system and the flagellum.

Numerous pathogenic bacteria contain luxS, which is required for autoinducer-2 production. Here, we demonstrate that Neisseria meningitidis contains a functional copy of luxS that is necessary for full meningococcal virulence; strains with a luxS deletion are defective for bacteremia, a prerequisite of meningococcal pathogenesis.

RpoE1, an extracytoplasmic function sigma factor, is a repressor of the flagellar system in Brucella melitensis Unité de Recherche en Biologie Molé culaire (URBM), Faculté s Universitaires Notre-Dame de la Paix Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, BelgiumThe genome of Brucella melitensis contains genes coding for the sigma factors RpoD, RpoN, RpoH1, RpoH2, RpoE1 and RpoE2. Previously published data show that B. melitensis is flagellated and that an rpoE1 mutant overexpresses the flagellar protein FlgE. In this study, we demonstrate that mutation of rpoE1 causes an overexpression of the flagellar genes fliF, flgE, fliC, flaF and flbT, correlating with the production of a longer filament and thereby demonstrating that RpoE1 acts as a flagellar repressor. Moreover, mutation of rpoE1 increases the promoter activity of the flagellar master regulator ftcR, suggesting that RpoE1 acts upstream of ftcR. Together, these data show that RpoE1 represses the flagellar synthesis and filament length in B. melitensis. INTRODUCTIONBrucellae are Gram-negative, intracellular pathogenic bacteria that cause brucellosis in a variety of mammals, including humans. For a long time, they were considered as being unflagellated. However, a sheathed flagellum has recently been discovered in Brucella melitensis and flagellar mutants are found to be impaired for infection in vivo (Ferooz & Letesson, 2010;Fretin et al., 2005;Zygmunt et al., 2006).The bacterial flagellum is a complex organelle used for motility and consists of at least three structural elements, the basal body, the hook and the filament (Macnab, 1999). The basal body, working as a motor, is embedded within the cell envelope and is anchored in the cytoplasmic membrane via the MS-ring structure, while the hook and filament, which function as a universal joint and a propeller, respectively, extend outwards from the cells (Minamino et al., 2008).Sigma and anti-sigma factors play important roles in the regulation of the flagellar genes (Smith & Hoover, 2009). The genome of B. melitensis has revealed the presence of genes encoding six sigma factors (rpoD, rpoH1, rpoH2, rpoE1, rpoE2 and rpoN) (Delory et al., 2006). The rpoD gene encodes the housekeeping sigma factor, the rpoH1 and rpoH2 genes encode two s 32 homologues, rpoE1 and rpoE2 encode two extracytoplasmic function (ECF) sigma factors and the rpoN gene encodes a s 54 homologue. The phenotypic characterizations were done on the five nonessential sigma factor mutants DrpoH1, DrpoH2, DrpoE1, DrpoE2 and DrpoN (Delory et al., 2006). Interestingly, at early growth phase in rich liquid medium, DrpoE1 overproduces the flagellar hook protein FlgE, suggesting that the flagellar system synthesis could be downregulated by the ECF sigma factor RpoE1 in B. melitensis (Delory et al., 2006).In this study, we demonstrate that the ECF sigma factor RpoE1 is a flagellar repressor in B. melitensis and that RpoE1 controls the length of the flagellar filament. METHODSBacterial strains and culture conditions. All strains and plasmids used ...