Fig. 2

Activation of the sigX promoter by culture supernatants. Test biofilms (8 h old) of the reporter strain S. mutans SMP _sigX GFP were used to test the activity of culture supernatants. Fluorescence intensity was determined after 3 h of incubation. a The reporter biofilm detected XIP in the medium above a concentration of 0.5 μM. b Fluorescence in the reporter biofilm was induced by culture supernatants from biofilms of S. mutans and A. act. cultivated together for 6 – 12 h, but not from single species biofilms or dual species biofilms at 4 h and 24 h of co-cultivation. c The reporter biofilm was challenged with culture supernatants from dual special biofilms of A. act with mutants of S. mutans carrying deletions of QS genes. Deletion of comS rendered culture supernatants inactive. d Effect of deletions of histidine kinases from two-component signal transduction systems of S. mutans on the activity of culture supernatants from biofilms with A. act. Deletion of liaS renders culture supernatants inactive. e-f Analysis of the ΔliaS mutant of S. mutans. e Culture supernatants from biofilms of S. mutans ΔliaS and A. act. cultivated separately or together for 4 – 24 h did not induce fluorescence in the reporter biofilm. f XIP induced expression of sigX in the wild-type S. mutans, but not in the ΔliaS mutant. Expression of sigX was determined by q-RT-PCR of sigX in the absence or presence of 0.5 μM XIP. The data were normalized to sigX expression in an uninduced S. mutans wild-type biofilm. Mean and standard deviation of three experiments are shown for a–e, and of two independent experiments (I and II) in f