Effect of protoporphyrin IX limitation on porphyromonas gingivalis

Porphyromonas gingivalis has been shown to require hemin or hemoglobin for in vitro growth. We have previously shown that protoporphyrin IX and inorganic iron can replace the hemin requirement, suggesting that the hemin requirement of this microorganism is actually a porphyrin requirement. We examined the effect of protoporphyrin IX limitation to P. gingivalis strain A7A1-28 in the presence of sufficient iron on growth characteristics, proteolytic enzyme production, virulence in a mouse abscess model, and expression of membrane proteins. Bacterial cells were grown in medium varying between 0 to 5 μM protoporphyrin IX. Protoporphyrin IX levels < 0.25 μM reduced growth by at least 50%. Protoporphyrin IX availability did not affect proteolytic enzyme production or virulence in a mouse abscess model. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane preparations demonstrated that protoporphyrin IX limitation induced the expression of new proteins at 42, 34, 30, 29, and 18 kDa and suppressed the production of proteins at 47,27,17, and 15 kDa. These studies suggest that in vivo protoporphyrin availability may modulate membrane protein expression and in turn affect host immune responses against P. gingivalis.