The influence of haemin levels on growth and enzyme production by Porphyromonas gingivalis in continuous culture.

Porphyromonas gingivalis was grown in continuous culture in brain heart infusion medium with haemin (5 microgm 1(-1) to 10 mg 1(-1)). Growth was haemin-limited up to 400 microgm 1(-1), and steady-state growth could not be obtained in the absence of haemin. It was confirmed that protoporphyrin IX could replace the haemin requirement. The results indicate that P. gingivalis has more than one uptake system for haemin, one of which is high affinity. The effect of haemin on hydrolytic enzyme production revealed a complex picture. Trypsin-like protease activity peaked at 200 microgm 1(-1) with a substantial and highly significant reduction at high (2 and 10 mg 1(-1)) concentrations of haemin. Alkaline phosphatase also peaked around 100 to 400 microgm 1(-1) while N-acetyl-beta-glucosaminidase was not greatly affected except that a greater proportion of enzyme was secreted into the medium at the lowest haemin concentration. In general, haemin-limitation enhanced export of the hydrolytic enzymes to the extracellular vesicle fraction. Protoporphyrin IX at 2 mg 1(-1) caused a highly significant reduction i the production of all three enzymes.