Advances in Rickettsia Pathogenicity

Balraj, P.; Renesto, Patricia; Raoult, Didier

doi:10.1111/j.1749-6632.2009.04517.x

Cited by 27 publications

(22 citation statements)

References 91 publications

(222 reference statements)

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“…This family is currently composed of two genera, Rickettsia and Orientia ; in both, bacteria are mainly associated with arthropod hosts and often infect vertebrates [1]. Infection with Rickettsia and Orientia in vertebrates is mediated by blood-sucking arthropods such as ticks and lice [2]. Due to their great medical significance, the molecular mechanisms underlying rickettsial infections have been investigated extensively [3], [4].…”

Section: Introductionmentioning

confidence: 99%

Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae

et al. 2012

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BackgroundThe order Rickettsiales comprises Gram-negative obligate intracellular bacteria (also called rickettsias) that are mainly associated with arthropod hosts. This group is medically important because it contains human-pathogenic species that cause dangerous diseases. Until now, there has been no report of non-phagotrophic photosynthetic eukaryotes, such as green plants, harboring rickettsias.Methodology/Principal FindingsWe examined the bacterial endosymbionts of two freshwater volvocalean green algae: unicellular Carteria cerasiformis and colonial Pleodorina japonica. Epifluorescence microscopy using 4′-6-deamidino-2-phenylindole staining revealed the presence of endosymbionts in all C. cerasiformis NIES-425 cells, and demonstrated a positive correlation between host cell size and the number of endosymbionts. Strains both containing and lacking endosymbionts of C. cerasiformis (NIES-425 and NIES-424) showed a >10-fold increase in cell number and typical sigmoid growth curves over 192 h. A phylogenetic analysis of 16 S ribosomal (r)RNA gene sequences from the endosymbionts of C. cerasiformis and P. japonica demonstrated that they formed a robust clade (hydra group) with endosymbionts of various non-arthropod hosts within the family Rickettsiaceae. There were significantly fewer differences in the 16 S rRNA sequences of the rickettsiacean endosymbionts between C. cerasiformis and P. japonica than in the chloroplast 16 S rRNA or 18 S rRNA of the host volvocalean cells. Fluorescence in situ hybridization demonstrated the existence of the rickettsiacean endosymbionts in the cytoplasm of two volvocalean species.Conclusions/SignificanceThe rickettsiacean endosymbionts are likely not harmful to their volvocalean hosts and may have been recently transmitted from other non-arthropod organisms. Because rickettsias are the closest relatives of mitochondria, incipient stages of mitochondrial endosymbiosis may be deduced using both strains with and without C. cerasiformis endosymbionts.

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Section: Introductionmentioning

confidence: 99%

Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae

et al. 2012

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“…Although previous studies have demonstrated that antibodies against Adr1 in R. conorii and Adr2 in R. prowazekii can prevent rickettsiae from entering host cells [39], [41], the functions of the 5 novel SEPs of R. rickettsii remain to be described. To assay the potential effects of specific antibodies against these SEPs on the interaction of R. rickettsii with vascular endothelial cells, sera from mice immunized with each of the 5 rSEPs were applied to neutralize R. rickettsii in vitro .…”

Section: Discussionmentioning

confidence: 98%

“…Rickettsial adhesins Adr1 and Adr2 were respectively identified in two strong spots in the SEP profile of R. rickettsii . Both of these proteins have been previously recognized in R. prowazekii [39], R. conorii [40], and R. heilongjiangensis [16], and shown to participate in rickettsial adhesion and entry into the host cells [39]–[41] since antibody to Adr1 in R. conorii and antibody to Adr2 in R. prowazekii could efficiently inhibit rickettsia invasion of host cells [39], [41]. OmpW was previously identified in R. heilongjiangensis [16] and is typically localized to the outer membrane of Gram-negative bacteria and associated with bacterial resistance to various forms of environmental stress [42].…”

Section: Discussionmentioning

confidence: 99%

Identification of Novel Surface-Exposed Proteins of Rickettsia rickettsii by Affinity Purification and Proteomics

Gong

Xiong

et al. 2014

PLoS ONE

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Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, is the most pathogenic member among Rickettsia spp. Surface-exposed proteins (SEPs) of R. rickettsii may play important roles in its pathogenesis or immunity. In this study, R. rickettsii organisms were surface-labeled with sulfo-NHS-SS-biotin and the labeled proteins were affinity-purified with streptavidin. The isolated proteins were separated by two-dimensional electrophoresis, and 10 proteins were identified among 23 protein spots by electrospray ionization tandem mass spectrometry. Five (OmpA, OmpB, GroEL, GroES, and a DNA-binding protein) of the 10 proteins were previously characterized as surface proteins of R. rickettsii. Another 5 proteins (Adr1, Adr2, OmpW, Porin_4, and TolC) were first recognized as SEPs of R. rickettsii herein. The genes encoding the 5 novel SEPs were expressed in Escherichia coli cells, resulting in 5 recombinant SEPs (rSEPs), which were used to immunize mice. After challenge with viable R. rickettsii cells, the rickettsial load in the spleen, liver, or lung of mice immunized with rAdr2 and in the lungs of mice immunized with other rSEPs excluding rTolC was significantly lower than in mice that were mock-immunized with PBS. The in vitro neutralization test revealed that sera from mice immunized with rAdr1, rAdr2, or rOmpW reduced R. rickettsii adherence to and invasion of vascular endothelial cells. The immuno-electron microscopic assay clearly showed that the novel SEPs were located in the outer and/or inner membrane of R. rickettsii. Altogether, the 5 novel SEPs identified herein might be involved in the interaction of R. rickettsii with vascular endothelial cells, and all of them except TolC were protective antigens.

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“…prowazekii (RP828) and R . conorii Adr2(RC1282) described a protein modeled after the Neisseria meningitidis NspA [24]. This initial analysis depicted a protein containing 10 trans-membrane β-strands and five extracellular domains.…”

Section: Discussionmentioning

confidence: 99%

Expression of Rickettsia Adr2 protein in E. coli is sufficient to promote resistance to complement-mediated killing, but not adherence to mammalian cells

2017

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Bacteria exposed to host serum are subject to the antibacterial effects to the complement system. However, pathogenic microorganisms have evolved mechanisms of evading this immune attack. We have previously demonstrated that at least two R. conorii antigens, RC1281/Adr1 and OmpB β-peptide, contribute to the evasion of complement-mediated killing by binding the complement regulatory proteins vitronectin and factor H. RC1282/Adr2, a protein related to Adr1, is predicted to share similar structural features, suggesting that this protein may also contribute to evasion of complement-mediated killing. Interestingly, the R. prowazekii Adr1 and Adr2(RP828) proteins were originally found to interact with host cell surface proteins, suggesting their putative roles as adhesins in this pathogenic rickettsial species. In this study, we expressed both R. conorii and R. prowazekii Adr2 on the surface of a non-adherent, serum-sensitive strain of E. coli to examine the potential role of this protein to mediate evasion of complement-mediated killing and adherence to host cells. We demonstrate that, similar to R. conorii Adr1, R. conorii and R. prowazekii Adr2 are sufficient to mediate serum resistance and to promote interaction with the host complement regulator vitronectin. Furthermore, we demonstrate that expression of Adr2 in a non-adherent strain of E. coli is insufficient to mediate adherence to cultured mammalian endothelial cells. Together, our data demonstrate that the R. conorii and R. prowazekii Adr2 protein does not participate in the interactions with mammalian cells, but rather, participates in the evasion of killing by complement.

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Advances in Rickettsia Pathogenicity

Cited by 27 publications

References 91 publications

Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae

Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae

Identification of Novel Surface-Exposed Proteins of Rickettsia rickettsii by Affinity Purification and Proteomics

Expression of Rickettsia Adr2 protein in E. coli is sufficient to promote resistance to complement-mediated killing, but not adherence to mammalian cells

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