Abstract
Porphyromonas gingivalis is a Gram‐negative black pigmenting anaerobe that is unable to synthesize heme [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. Porphyromonas gingivalis expresses several proteinaceous hemin‐binding sites, which are important in the binding/transport of heme/hemin from the host. It also synthesizes 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‐bisheme {[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‐bisheme 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 with 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‐bisheme on the cell surface and pigmentation is dependent on the presence of A‐LPS.
Highlights
The black pigmenting anaerobe Porphyromonas gingivalis is a major pathogen in chronic adult periodontal disease[1] and has recently been described as a “keystone pathogen” with wide-ranging effects critical for the development of dysbiosis and disease progression.[2]
The hemin binding properties of P. gingivalis have been a major area of study and interest for several years
Iron utilization systems in P. gingivalis are quite complex and several proteins have been implicated in hemin release from the host, to its transport and deposition on the bacterial cell surface
Summary
The black pigmenting anaerobe Porphyromonas gingivalis is a major pathogen in chronic adult periodontal disease[1] and has recently been described as a “keystone pathogen” with wide-ranging effects critical for the development of dysbiosis and disease progression.[2]. Hemin [Fe(III)-p rotoporphyrin IX-Cl] is an important requirement for growth of P. gingivalis[3,4] and as the organism is not able to synthesize protoporphyrin IX ring[5,6] and does not contain any siderophores,[7,8] the major source of heme [Fe(II)-protoporphyrin IX] is the host. We addressed the question whether the high abundance low-affinity hemin-binding site described by Tompkins et al.[22] may be one of the LPS of P. gingivalis To test this hypothesis, we examined a variety of isogenic mutant strains of P. gingivalis lacking Arg- gingipains, Lys-gingipain and defective in the biosynthesis of O-LPS and A-LPS for their ability to pigment and to bind hemin to whole cells and to LPS, de-phosphorylated LPS and de-lipidated LPS. We propose that the presence of A-LPS serves as a matrix for the deposition of μ-oxo-bisheme on the P. gingivalis cell surface
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