FIG. 4.

Decay of light emission of logarithmic-phase S. mutans cells at pH 6.0 with different substrate concentrations: 5 (•), 12,5 (∗), 25 (×), 50 (▴), 125 (■), and 250 (⧫) μM. The bioluminescent reaction in cells was triggered by the addition of different concentrations of d-luciferin, and the light emission of the cells was immediately measured with a microtitration plate luminometer. The values are the means of two independent measurements. The variation between the measurements was less than 10%. RLU, relative light units.