Desulfovibrio fairfieldensis-Derived Outer Membrane Vesicles Damage Epithelial Barrier and Induce Inflammation and Pyroptosis in Macrophages

Sulfate-reducing bacteria Desulfovibrio fairfieldensis is an opportunistic pathogen that widely exists in the human intestine and can cause severe infectious diseases. However, the mechanisms contributing to its pathogenesis remain of great interest. In this study, we aim to investigate the outer membrane vesicles (OMVs) secreted by D. fairfieldensis and their pathogenic effect. The OMVs separated by ultracentrifugation were spherical and displayed a characteristic bilayer lipid structure observed by transmission electron microscopy, with an average hydrodynamic diameter of 75 nm measurement using the particle size analyzer. We identified 1496 and 916 proteins from D. fairfieldensis and its OMVs using label-free non-target quantitative proteomics, respectively. The 560 co-expressed proteins could participate in bacterial life activities by function prediction. The translocation protein TolB, which participates in OMVs biogenesis and transporting toxins was highly expressed in OMVs. The OMVs inhibited the expression of tight junction proteins OCCLUDIN and ZO-1 in human colonic epithelial cells (Caco-2). The OMVs decreased the cell viability of monocyte macrophages (THP-1-Mφ) and activated various inflammatory factors secretion, including interferon-γ (IFN-γ), tumor necrosis factor (TNF-α), and many interleukins. Further, we found the OMVs induced the expression of cleaved-gasdermin D, caspase-1, and c-IL-1β and caused pyroptosis in THP-1-Mφ cells. Taken together, these data reveal that the D. fairfieldensis OMVs can damage the intestinal epithelial barrier and activate intrinsic inflammation.