Induction of luminescence in V. harveyi by CM from S. pyogenes . (A) Induction of luminescence in V. harveyi reporter strain BB170 by CM of wild-type and luxS-deficient mutants. RDN29: wild-type M1 strain, EC460: RDN29 (pEC82), EC478: isogenic luxS-deficient mutant, EC489: EC478 (pEC82), EC490: EC478 complemented with pEC83. THY medium and CM of DH5-α (AI-2 deficient) were used as negative controls; CM of BB170 was used as positive control. CM were prepared from cultures at late-logarithmic phase of growth. The luminescence values expressed in specific light units (SLU = RLU (relative light units)/OD620 nm) (y axis) are plotted versus time (h) (x axis). Data shown are representative of three independent experiments. Similar data were obtained with CM of the RDN02 (M19 serotype) derivative strains. (B) Fold induction of V. harveyi BB170 luminescence by CM of RDN29 and EC478. CM was prepared from cultures at mid-logarithmic (ML), late-logarithmic (LL), early-stationary (ST-1) and stationary phase (ST-2) of growth. Fold induction corresponds to the SLU values obtained with the CM of the analyzed strains versus those obtained with the CM of the negative control THY. Fold induction was calculated after ~4 h of induction when the cell density begins to rise. Induction of luminescence with late-logarithmic CM from the luxS-deficient mutant was ~60 fold lower compared to CM from the parent wild-type strain. The average values and standard deviations of three independent experiments are shown. Similar data were obtained with CM of the RDN02 derivative strains.