The Predicted ABC Transporter AbcEDCBA Is Required for Type IV Secretion System Expression and Lysosomal Evasion by <i>Brucella ovis</i>

<div><p><i>Brucella ovis</i> is a major cause of reproductive failure in rams and it is one of the few well-described <i>Brucella</i> species that is not zoonotic. Previous work showed that a <i>B. ovis</i> mutant lacking a species-specific ABC transporter (Δ<i>abcBA</i>) was attenuated in mice and was unable to survive in macrophages. The aim of this study was to evaluate the role of this ABC transporter during intracellular survival of <i>B. ovis</i>. In HeLa cells, <i>B. ovis</i> WT was able to survive and replicate at later time point (48 hpi), whereas an Δ<i>abcBA</i> mutant was attenuated at 24 hpi. The reduced survival of the Δ<i>abcBA</i> mutant was associated with a decreased ability to exclude the lysosomal marker LAMP1 from its vacuolar membrane, suggesting a failure to establish a replicative niche. The Δ<i>abcBA</i> mutant showed a reduced abundance of the Type IV secretion system (T4SS) proteins VirB8 and VirB11 in both rich and acid media, when compared to WT <i>B. ovis</i>. However, mRNA levels of <i>virB1</i>, <i>virB8</i>, <i>hutC,</i> and <i>vjbR</i> were similar in both strains. These results support the notion that the ABC transporter encoded by <i>abcEDCBA</i> or its transported substrate acts at a post-transcriptional level to promote the optimal expression of the <i>B. ovis</i> T4SS within infected host cells.</p>