Brucella, a facultative intracellular bacterium, can survive and replicate in various cell types such as epithelial cell, fibroblasts and macrophage. Macrophage is the most important sites for the survival of Brucella in vivo. The mechanisms of pathogenesis are difficult to address, since the unknown virulence genes are still exist. RNA-seq is available to study transcriptional changes that occur during disease as a way to identify important virulence-related genes. Here we described and analyzed the transcriptional change of avirulent strain Brucella melitensis M5-90 (B. melitensis M5-90) during macrophage infection using RNA-seq technology. We detected 601 significant changed genes of which 428 were upregulated after infection. The upregulated gene L31 which involved in ribosome KEGG pathway was selected to illustrate its effect on virulence in a vaccine strain B. melitensis M5-90 and a virulent strain B. melitensis M28. Deletion of L31 significant attenuates the spleen colonization in model of M5-90 or M28 infection mouse at 7, 21 and 35 days post-infection (P < 0.05). We further examine the role of L31 in a macrophage cell infection model, and the result showed a significant reduction of intracellular M28ΔL31 cells at 48 h post-infection (P < 0.001). In total, our study provided a view of transcriptional landscape of B. melitensis M5-90 intracellular, and found L31 gene is required for the full virulence of B. melitensis.
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