Role of the Omp25/Omp31 Family in Outer Membrane Properties and Virulence ofBrucella ovis

Abstract

The genes coding for the five outer membrane proteins (OMPs) of the Omp25/Omp31 family expected to be located in the outer membrane (OM) of rough virulent Brucella ovis PA were inactivated to evaluate their role in virulence and OM properties. The OM properties of the mutant strains and of the mutants complemented with the corresponding wild-type genes were analyzed, in comparison with the parental strain and rough B. abortus RB51, in several tests: (i) binding of anti-Omp25 and anti-Omp31 monoclonal antibodies, (ii) autoagglutination of bacterial suspensions, and (iii) assessment of susceptibility to polymyxin B, sodium deoxycholate, hydrogen peroxide, and nonimmune ram serum. A tight balance of the members of the Omp25/Omp31 family was seen to be essential for the stability of the B. ovis OM, and important differences between the OMs of B. ovis PA and B. abortus RB51 rough strains were observed. Regarding virulence, the absence of Omp25d and Omp22 from the OM of B. ovis PA led to a drastic reduction in spleen colonization in mice. While the greater susceptibility of the ⌬omp22 mutant to nonimmune serum and its difficulty in surviving in the stationary phase might be on the basis of its dramatic attenuation, no defects in the OM able to explain the attenuation of the ⌬omp25d mutant were found, especially considering that the fully virulent ⌬omp25c mutant displayed more important OM defects. Accordingly, Omp25d, and perhaps Omp22, could be directly involved in the penetration and/or survival of B. ovis inside host cells. This aspect, together with the role of Omp25d and Omp22 in the virulence both of B. ovis in rams and of other Brucella species, should be thoroughly evaluated in future studies.The genus Brucella comprises six classical species (Brucella melitensis, B. abortus, B. suis, B. ovis, B. canis, and B. neotomae) that infect terrestrial mammals (41), although in recent years an increasing number of Brucella strains have been isolated from marine mammals and proposed to be included in two new species, B. cetaceae and B. pinnipediae (9).Brucella spp. may have smooth or rough lipopolysaccharide (S-LPS or R-LPS) depending on the presence or absence, respectively, of O-polysaccharide chains. Rough mutants derived from smooth Brucella strains show an important reduction in virulence (1,26,30,40,45). Accordingly, the O-polysaccharide chains of LPS are thought to be necessary for the pathogenicity of Brucella strains bearing S-LPS. However, B. ovis and B. canis lack O chains in the LPS but are pathogenic for rams and dogs, respectively, and induce long-lasting infections with high levels of splenic colonization in laboratory animals (34). Since O chains mask other components of the Brucella spp. outer membrane (OM), OM proteins (OMPs) are more exposed at the bacterial surface of rough B. ovis and B. canis (4, 7) and their involvement in virulence in rough Brucella strains may be more relevant than in smooth Brucella strains.The Brucella spp. Omp25/Omp31 family comprises seven homologous OMPs. Omp25 and Omp31...

Quorum-Sensing and BvrR/BvrS Regulation, the Type IV Secretion System, Cyclic Glucans, and BacA in the Virulence of Brucella ovis: Similarities to and Differences from Smooth Brucellae

“…Nevertheless, B. ovis is a naturally R Brucella species that is virulent in its natural host and in laboratory animal models (9,33,51). This ability of B. ovis to infect the host despite the absence of O-PS in the OM, together with its tropism for the male genital tract, is indicative of virulence mechanisms differing, at least in part, from those employed by S Brucella species, which are able to colonize the placenta and typically induce abortions.…”

“…ovis has never been reported as a human pathogen and mainly infects rams. Little is known about the virulence of B. ovis, although some clues have been obtained from a study that deciphered the whole genome sequence (53) and from a small number of studies performed with individual genes (9,33,51). Additionally, it is known that-similarly to S Brucella and in contrast to R derivatives of S strains (45)-B. ovis enters the macrophage through cholesterol-rich lipid rafts (36).…”

“…Strains of the genus Brucella may be smooth (S) or rough (R), depending on the presence or absence, respectively, of O-polysaccharide (O-PS) chains in the LPS. O-PS masks other components of the bacterial surface (6), and since R mutant (M) strains derived from S strains are impaired in the interaction with phagocytes and are attenuated in animal models of infection (22,40,44), it is considered a key virulence factor in S Brucella species (such as B. melitensis, B. abortus, and B. suis).Nevertheless, B. ovis is a naturally R Brucella species that is virulent in its natural host and in laboratory animal models (9,33,51). This ability of B. ovis to infect the host despite the absence of O-PS in the OM, together with its tropism for the male genital tract, is indicative of virulence mechanisms differing, at least in part, from those employed by S Brucella species, which are able to colonize the placenta and typically induce abortions.…”

Intruders below the Radar: Molecular Pathogenesis of Bartonella spp

“…Three to five representatives are present in the genome of every Bartonella species, and homologs are widespread among Rhizobiales but rare beyond this taxon (reference 294 and personal observation). The Hbps show considerable sequence similarity to members of the OMP25/31 family of Brucella (75), which are apparently crucial for several aspects of pathogenesis, although their molecular function is not known (74,276). Furthermore, homologies to the well-known Neisseria Opa proteins, which are critical mediators of host cell interaction involving invasion and immunomodulation (372, 388), have been described (296).…”

Bartonella and Brucella--Weapons and Strategies for Stealth Attack

“…Hemin-binding proteins (Hbps in Bartonella and OMP25/31 in Brucella) constitute a family of porin-like outer membrane proteins that bind hemin (Battisti et al 2006;Dabo et al 2006;Delpino et al 2006;Caro-Hernandez et al 2007). Hemin is essential for Bartonella growth (Sander et al 2000), rendering these bacteria the most hemin-dependent microbes.…”