Growth stimulation of Porphyromonas endodontalis by hemoglobin and protoporphyrin IX

Porphyromonas endodontalis, like other Porphyromonas species, has a complex set of nutritional requirements. In addition to being an obligate anaerobe , the bacterium must be grown in a complex medium consisting of amino acids , reducing agents and heme compounds. P. endontalis accumulates high concen trations of heme pigments to the extent that colonies appear black on blood agar. This accumulation of heme and the need for these compounds has been characterized as iron requirements by these species. However. in our studie s, P. endodontalis demonstrated growth dependence on hemoglobin or protopor phyrin IX but not on free iron. Iron added to other heme compounds actually decreased growth stimulation by porphyrin-containing compounds. P. endodon talis actively transported free iron, but this process did not appear to be critical for growth. The maximum stimulation of growth by protoporphyrin I X, under conditions of iron deprivation, suggests that P. endodontalis requ ires the porphyrin moiety as a growth factor.