Intracellular rescuing of a B. melitensis 16M virB mutant by co-infection with a wild type strain

Abstract

Brucella is a broad-range, facultative intracellular pathogen that can survive and replicate in an endoplasmic reticulum (ER)-derived replication niche by preventing fusion of its membrane-bound compartment with late endosomes and lysosomes. This vacuolar hijacking was demonstrated to be dependent on the type IV secretion system VirB but no secreted effectors have been identified yet. A virB mutant is unable to reach its ER-derived replicative niche and does not multiply intracellularly. In this paper, we showed that, by co-infecting bovine macrophages or HeLa cells with the wild type (WT) strain of Brucella melitensis 16M and a deletion mutant of the complete virB operon, the replication of Δ virB is rescued in almost 20% of the co-infected cells. Furthermore, we demonstrated that co-infections with the WT strains of Brucella abortus or Brucella suis were equally able to rescue the replication of the B. melitensis Δ virB mutant. By contrast, no rescue was observed when the WT strain was given 1 h before or after the infection with the Δ virB mutant. Finally, vacuoles containing the rescued Δ virB mutant were shown to exclude the LAMP-1 marker in a way similar to the WT containing vacuoles.