The stringent response mediator Rsh is required for Brucella melitensis and Brucella suis virulence, and for expression of the type IV secretion system virB

Marie Dozot, Rose-Anne Boigegrain, Rose-May Delrue, Régis Hallez, Safia Ouahrani-Bettache, Isabelle Danese, Jean-Jacques Letesson, Xavier De Bolle, Stephan Köhler

Research output: Contribution to journalArticle


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.
Original languageEnglish
Pages (from-to)1791-802
Number of pages12
JournalCellular microbiology
Issue number11
Publication statusPublished - 2006


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