FIG. 2.

RbsB inhibits V. harveyi BB170 bioluminescence induced by A. actinomycetemcomitans AI-2 (A) and V. harveyi AI-2 (B) in a dose-dependent manner. Purified RbsB protein (0.3 to 5,000 ng per ml) was incubated with partially purified AI-2 from A. actinomycetemcomitans or with conditioned AI medium from an overnight V. harveyi culture for 30 min at 30°C. After subsequent addition of V. harveyi BB170 cells, bioluminescence was measured at hourly intervals by using a Wallac Victor³ microtiter plate reader. The data shown represent the 6-h time point after the addition of AI-2, at which time the positive control (V. harveyi BB170 cells exposed to conditioned AI medium from an overnight V. harveyi culture) exhibited approximately 1,100- to 1,300-fold induction of bioluminescence over that of the negative-control reaction mixture containing sterile AI medium. Reactions were performed in triplicate.