THE EFFECT OF GROWTH-RATE AND HEMIN ON THE VIRULENCE AND PROTEOLYTIC ACTIVITY OF PORPHYROMONAS-GINGIVALIS W50

Porphyromonas gingivalis strain W50 was grown under haemin-limitation and haemin-excess conditions in a chemostat at pH 7.5. The maximum spe cific growth rate (mu(max)) was determined at both haemin concentratio ns (mu(max) = 0.236+/-0.052 and 0.271+/-0.039 h-(1), respectively). Th is enabled dilution rates to be adjusted so that the virulence and enz yme activity of haemin-limited and haemin-replete cells could be compa red at identical relative growth rates (mu(rel)) of 0.25, 0.50 and 0.7 5 of their respective mu(max). The data showed that the fastest growin g cells were significantly more virulent than those grown more slowly, irrespective of haemin concentration. However, at each growth rate te sted, cells grown under haemin-excess conditions were always more viru lent than haemin-limited cells. Trypsin-like enzyme activity of whole cultures was also greater at each growth rate under haemin-excess cond itions while, conversely, collagenolytic activity was generally higher in haemin-limited cultures. Thus, although growth rate had an effect on the virulence and enzyme activity of P. gingivalis, the availabilit y of haemin for growth was the most significant factor.