Methods for Functional Characterization of the Type IX Secretion System of Porphyromonas gingivalis

The type IX secretion system (T9SS) is a protein secretion system for gingipain proteases and is found on the cell surface of Porphyromonas gingivalis. Proteins secreted by T9SS contain a signal peptide, functional domains, an immunoglobulin (Ig)-like domain, and a C-terminal domain (CTD). Thirty genes on the P. gingivalis chromosome encode proteins that possess the CTD, which is important for T9SS-mediated translocation to the cell surface across the outer membrane. In T9SS mutant strains, proteins accumulate as precursors in the cell and therefore exhibit a phenotype similar to that of secreted protein-deficient mutants. Black pigment productivity and hemagglutination are phenotypic features of P. gingivalis associated with the activity of gingipains. In P. gingivalis T9SS mutants, unprocessed gingipains with high molecular weights accumulate in the cell, and colony pigmentation and hemagglutination are not observed in the same phenotype as a gingipain null mutant.