Hemin Binding by Porphyromonas gingivalis strains is dependent on the presence of A-LPS

Summary

Porphyromonas gingivalis is a Gram-negative black pigmenting anaerobe unable to synthesise haem (Fe (II)-protoporphyrin IX) or hemin (Fe(III)-protoporphyrin IX-Cl) which are important growth/virulence-factors, and must therefore derive them from the host P. gingivalis expresses several proteinaceous hemin -binding-sites which are important in the binding/ transport of haem/hemin from the host. P. gingivalis also synthesises several virulence factors, namely cysteine-proteases Arg- and Lys-gingipains and two lipopolysaccharides (LPS), O-LPS and A-LPS. The gingipains are required for the production of the black pigment, μ-oxo-bishaem ([Fe(III)PPIX]₂ O), which is derived from hemoglobin and deposited on the bacterial cell-surface leading to the characteristic black colonies when grown on blood agar. In this study we investigated the role of LPS in the deposition of μ-oxo-bishaem on the cell-surface.

A P. gingivalis mutant defective in the biosynthesis of Arg-gingipains, namely rgpA/rgpB produces brown colonies on blood agar and mutants defective in Lys-gingipain (kgp) and LPS biosynthesis namely porR, waaL, wzy and pg0129 (α-1, 3 -mannosyltransferase) produce non-pigmented colonies. However, only those mutants lacking A-LPS showed reduced hemin-binding when cells in suspension were incubated with hemin. Using native, de-O-phosphorylated and de-lipidated LPS from P. gingivalis W50 and porR strains, we demonstrated that hemin-binding to O-polysaccharide (PS) and to the lipid A moiety of LPS was reduced compared to hemin-binding to A-PS. We conclude that A-LPS in the outer-membrane of P. gingivalis serves as a scaffold/ anchor for the retention of μ-oxo-bishaem on the cell surface and pigmentation is dependent on the presence of A-LPS.

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