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.