The <i>Porphyromonas gingivalis</i> lipid A 1-phosphatase LpxE requires a functional type IX secretion system for its activity

<b>Background:</b> <i>Porphyromonas gingivalis</i> is a Gram-negative bacterium that plays a central role in the development of periodontal disease. It uses a type IX secretion system (T9SS) to export virulence factors to the bacterial surface where they are attached to A-LPS, one of the two forms of lipopolysaccharide (LPS) produced in <i>P. gingivalis</i>, and then packaged into outer membrane vesicles (OMVs). We previously showed that 1-P dephosphorylation of the lipid A component of LPS is regulated by the T9SS outer membrane protein PorV, and this is linked to membrane destabilisation and OMV blebbing/formation. <b>Objective:</b> This study aimed to investigate whether other T9SS outer membrane proteins are required for correct OMV biogenesis. <b>Design:</b> We examined gingipain activity, gingipain secretion, A-LPS production, OMV morphology, and lipid A structure in <i>P. gingivalis</i> W50, T9SS mutant strains, and a lipid A 1-phosphatase (Δ<i>lpxE</i>) mutant strain. <b>Results:</b> A functional T9SS is required for LpxE activity and correct vesicle formation, and this is likely through the function of an exported type IX-cargo protein. <b>Conclusion:</b> This study provides insight into a new mechanism that links type IX cargo sorting with OMV blebbing, which may also be present in other <i>Bacteroidota</i> that colonise the gut and oral cavity.