Figure 2. Transient production of long-chain AHLs by B. melitensis in liquid culture.

The B. melitensis QS reporter strain was grown in 2YT and cell density was determined when fluorescence intensity of GFP(ASV) was assessed by flow cytometry (5×10⁴ events acquired). (A) Growth curve of the B. melitensis QS reporter strain. Numbers represent the 4 distinct phases of growth. OD₆₀₀, optical density at 600nm. (B) Histograms of GFP(ASV) fluorescence intensity representative of the growth phases represented in A. The B. melitensis control strain was used as a negative control. In (B2), the peak of GFP(ASV) fluorescence intensity due to endogenous AHLs was compared with results obtained after a 4h-incubation of the B. melitensis QS reporter strain with synthetic C12-HSL or 3-oxo-C12-HSL (bacteria from the early log phase were used). The insets show differential interference contrast (DIC) and FITC fluorescence microscopy of (from top to bottom) the negative control strain, the QS reporter strain in the absence of exogenous AHL and incubated with C12-HSL 0.1nM, with C12-HSL 1nM, and with 3-oxo-C12-HSL 0.1 nM respectively. Results are representative of three independent experiments.