AHL signal assay
The isolation and purification of AHLs were performed as described by Kim et al . (2004). The culture supernatants from time course cultures of P. ananatis PA13 and mutants were extracted with ethyl acetate (1:1). The ethyl acetate layer was dried, and the residue was dissolved in methanol. The ethyl acetate extracts were applied to C18 reversed-phase TLC plates (Merck) and developed with 60% methanol. The TLC plates were dried in a fume hood and overlaid with soft agar containing Chromobacterium violaceum CV026 cells cultured overnight. The plates were incubated at 28°C overnight.