FIG. 3.

Specific activity of H. pylori AI-2 is maximal in early log phase and decreases in late log phase. H. pylori Alston was grown for 31 h under microaerobic conditions in BBH. At 0, 5, 8, 10, 25, and 31 h, cell-free culture fluids were prepared. Cell density was measured by diluting and plating cell aliquots at each time point (line). AI-2 activity was assayed for the ability to stimulate expression of bioluminescence in the V. harveyi reporter strain BB170 (bars). Specific activity was determined by dividing the fold activation of luminescence values by the total number of bacterial cells present at each time point.