Brucellosis 2003 proceedings - PHIDIAS

Short Oral Communications
Immunology, pathogenesis and host-pathogen interaction
PO8- CHARACTERIZATION OF QUORUM SENSING MOLECULAR ACTORS
FROM Brucella melitensis 16M.
C. Deschamps, R-M Delrue, J.J. Letesson and X. De Bolle. Unité de Recherche en Biologie
Moléculaire (URBM), Laboratoire d’Immunologie et de Microbiologie, Facultés Universitaires Notre-
Dame de la Paix, Namur, Belgium.
The regulation of gene expression by Quorum Sensing is based on 3 actors:
(i) a diffusible pheromone that increases in concentration as a function of cell density,
(ii) an enzyme catalyzing pheromone production (synthase) and (iii) a transcriptional
regulator which, when associated with pheromone, can regulate target genes.
Quorum Sensing allows bacteria to communicate and coordinate gene expression
and therefore controls the behaviour of an entire community.
In culture supernatant of B. melitensis 16M, we previously identified a N-acyl
homoserine lactone (HSL) type pheromone suggesting that Brucella have a Quorum
Sensing system. This pheromone negatively regulates the transcription of the virB
operon encoding type IV secretion system involved in Brucella pathogenicity.
Therefore study of this communication system might give insights into Brucella
virulence.
Two coding sequences, babR and vjbR encoding Quorum Sensing regulators
homologues have been identified by different screenings in B. melitensis. It has been
shown that VjbR is an activator of the virB operon. The expression level of babR,
vjbR and virB is analysed quantitatively during bacterial growth in wild type, BabR or
VjbR mutant backgrounds with or without HSL. For this study, we used promoter of
interest-luxAB reporter fusions on a replicative plasmid in Brucella. Until now, no HSL
synthase has been identified in Brucella. Based on sequence similarities, an
homologue of a novel HSL synthase, HdtS in Pseudomonas fluorescens, has been
identified in the genome of B. melitensis. We investigate the production of HSL by
this putative synthase in Brucella.
PO9- VirB2 IS REQUIRED FOR THE FUNCTION OF THE Brucella abortus TYPE
IV SECRETION SYSTEM.
Andreas B. den Hartigh, Hortensia G. Rolán and Renée M. Tsolis. Texas A&M University System
Health Science Center, Departement of Medical Microbiology and Immunology, College Station, TX,
USA.
The Brucella Type IV secretion system (T4SS) is encoded by the virB1 –
virB12 genes. We found previously that transposon insertions in the virB1 3’ region or
in virB10 render Brucella unable to initiate persistent infection in mice. In
Agrobacterium VirB2 has been shown to form a pilus with which VirB1 has been
shown to associate. In order to determine whether these putative pilus-associated
proteins are required for virulence and for function of the T4SS, we generated polar
and non-polar mutants of virB1 and virB2, and tested them for virulence. Our
preliminary results show that both polar and non-polar virB2 mutants are significantly
attenuated for growth in macrophages and in mice. These findings suggest that VirB2
is essential for the function of the B. abortus T4SS.
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Brucellosis 2003 International Research Conference