The putative type 4 secretion system effector BspD is involved in maintaining envelope integrity of the pathogen .

UNLABELLED

Brucellosis is a debilitating disease caused by the Gram-negative, facultative intracellular zoonotic pathogen En route to its intracellular replicative niche, encounters various stressful environments that may compromise envelope integrity. Here we show that the proposed type 4 secretion system (T4SS) effector BspD is a conserved protein of the Rhizobiales, which does not show signs of co-evolution with the presence of a T4SS or a certain lifestyle. We further present data indicating that BspD is critical for the envelope integrity of in the stationary phase and in the presence of EDTA, a compound known to destabilize the outer membrane. Deletion of resulted in abnormal bacterial morphologies, indicating its involvement in maintaining envelope integrity. Additionally, the absence of BspD led to the formation of fewer and smaller intracellular microcolonies in a macrophage infection model. From our observations, we propose that BspD of is critical for preserving the integrity of the bacterial envelope, particularly under stressful conditions, which may enhance 's ability to survive within host cells.

IMPORTANCE

Brucellosis, caused by the intracellular pathogen , poses a significant health threat. Understanding how adapts to stressful environments is crucial. This study unveils BspD, a conserved protein within the Rhizobiales order, as a key player in maintaining 's envelope integrity. Remarkably, BspD's presence within the Rizobiales appears independent of the presence of a T4SS or a specific lifestyle. Deletion of resulted in compromised envelope integrity, abnormal bacterial morphologies, and reduced intracellular microcolony formation. These findings underscore BspD's critical role, particularly in stressful conditions like the stationary phase and EDTA exposure, and highlight its significance for the survival of within host cells. This elucidation deepens our understanding of pathogenesis and may inform future therapeutic strategies against brucellosis.