The Porphyromonas gingivalis lipid A 1-phosphatase LpxE requires a functional type IX secretion system for its activity.

Background: Porphyromonas gingivalis 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 P. gingivalis, 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. Objective: This study aimed to investigate whether other T9SS outer membrane proteins are required for correct OMV biogenesis. Design: We examined gingipain activity, gingipain secretion, A-LPS production, OMV morphology, and lipid A structure in P. gingivalis W50, T9SS mutant strains, and a lipid A 1-phosphatase (ΔlpxE) mutant strain. Results: 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. Conclusion: This study provides insight into a new mechanism that links type IX cargo sorting with OMV blebbing, which may also be present in other Bacteroidota that colonise the gut and oral cavity.