Figure 3. The decrease in Brucella AHLs activity during in vitro growth is linked to aibP expression.

(A) The relative amount of aibP mRNA (black forms) during vegetative growth of B. melitensis (open forms) in 2YT medium was determined by qRT-PCR. Result is representative of three independent experiments. Error bars represent standard deviation from biological triplicates. OD₆₀₀, optical density at 600nm; RQ, relative quantity. (B) The activity of endogenous long-chain AHLs was followed using the QS reporter system. B. melitensis wt (black forms) and ▵aibP (open forms) QS reporter strains were grown in 2YT and cell density was determined (triangle) for each culture when GFP(ASV) fluorescence intensity was evaluated (square). The activity of endogenous long-chain AHL(s) at each time is expressed as the geometric mean of GFP(ASV) fluorescence intensity measured by flow cytometry (5×10⁴ events acquired). The B. melitensis control strain was used as a negative control (not shown). Insert: the scale of the graph was modified for analysis in the wt strain. Results are representative of three independent experiments. Error bars represent standard deviation from biological triplicates.