Haemin (iron protoporphyrin IX) is an essential growth factor for the periodontal pathogen, Porphyromonas gingivalis. Iron protoporphyrin IX (IPP IX) binding to the avirulent P. gingivalis beige variant (W50/BE1) and the black-pigmenting parent wild-type strain W50 was quantified. W50/BE1 grown in a chemostat under haemin excess-bound IPP IX under both oxidising and reducing conditions but with both lower capacity and avidity than either the haemin-limited- and haemin-excess-grown parent strain W50. Rosenthal plots for W50/BE1 indicated cooperative binding. W50/BE1 cells expressed a 32 kDa outer membrane haemin-binding protein when grown under conditions of haemin excess, and this strain might serve as a useful source from which to isolate this protein. The reduced IPP IX binding ability of W50/BE1 may be the rate-limiting factor for haem uptake and explain the reduced virulence and slower rate of pigmentation of this strain.
Smalley, J. W., Birss, A. J., McKee, A. S., & Marsh, P. D. (1996). Haemin binding as a factor in the virulence of Porphyromonas gingivalis. FEMS Microbiology Letters, 141(1), 65–70. https://doi.org/10.1016/0378-1097(96)00209-1