Figure 4. Kinetics of metK, luxI, luxS and iaaM gene expression involved in AI-1, AI-2 and IAA production by D. chrysanthemi strain CFBP 2048^T.

AI-1 and AI-2 biosynthetic pathways are described in the legend to Fig. 3. A third signal, the indole-3-acetic acid (IAA) is synthesized by the indole-3-acetamine (IAM) pathway, in which l-tryptophan is first converted to IAM by the key enzyme of this pathway, the IaaM tryptophan-2-monooxygenase. IAM is then converted to IAA by IaaM hydrolase [36], [54]. Abundances of metK (checkered bars), luxI (white bars), luxS (black bars) and iaaM (grey bars) mRNAs were determined by RT-PCR experiments on RNA extracts from cells grown in PGA minimal medium (A) or M9 minimal medium supplemented with l-tryptophan (500 µg/ml) (B) and harvested at mid-exponential phase (1), late exponential phase (2), during the transition from exponential to stationary phases (3) or early stationary growth phase (4) followed by electrophoresis on 1% (m/v) agarose gels. Results were expressed as a ratio: synthase transcripts vs. 16S transcripts. The corresponding kinetics of AI-1 and AI-2 activities and IAA production in the supernatant of potato soft-rot Dickeya strain are shown at the top.