The stringent response mediator Rsh is required for Brucella melitensis and Brucella suis virulence, and for expression of the type IV secretion system virB.
Physiological adaptation of intracellular bacteria is critical for timely interaction with eukaryotic host cells. One mechanism of adaptation, the stringent response, is induced by nutrient stress via its effector molecule (p)ppGpp, synthesized by the action of RelA/SpoT homologues. The intracellular pathogen Brucella spp., causative agent of brucellosis, possesses a gene homologous to relA/spoT, named rsh, encoding a (p)ppGpp synthetase as confirmed by heterologous complementation of a relA mutant of Sinorhizobium meliloti. The Rsh deletion mutants in Brucella suis and Brucella melitensis were characterized by altered morphology, and by reduced survival under starvation conditions and in cellular and murine models of infection. Most interestingly, we evidenced that expression of virB, encoding the type IV secretion system, a major virulence factor of Brucella, was Rsh-dependent. All mutant phenotypes, including lack of VirB proteins, were complemented with the rsh gene of Brucella. In addition, RelA of S. meliloti functionally replaced Brucella Rsh, describing the capacity of a gene from a plant symbiont to restore virulence in a mammalian pathogen. We therefore concluded that in the intramacrophagic environment encountered by Brucella, Rsh might participate in the adaptation of the pathogen to low-nutrient environments, and indirectly in the VirB-mediated formation of the final replicative niche.
Dozot
Marie
M
Research Unit in Molecular Biology, University of Namur, 61 rue de Bruxelles, B-5000 Namur, Belgium.
Boigegrain
Rose-Anne
RA
Delrue
Rose-May
RM
Hallez
Régis
R
Ouahrani-Bettache
Safia
S
Danese
Isabelle
I
Letesson
Jean-Jacques
JJ
De Bolle
Xavier
X
Köhler
Stephan
S
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D017347:Brucella melitensis / Q000235:genetics* / Q000472:pathogenicity; D041021:Brucella suis / Q000235:genetics* / Q000472:pathogenicity; D002006:Brucellosis / Q000382:microbiology; D002478:Cells, Cultured; D017353:Gene Deletion; D015870:Gene Expression / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005816:Genetic Complementation Test / Q000379:methods; D006159:Guanosine Tetraphosphate / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation / Q000235:genetics; D012756:Sheep; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D014157:Transcription Factors; D037521:Virulence Factors; D006159:Guanosine Tetraphosphate