Bacterial Strains and Growth Conditions

The bacterial strains and plasmids used in this study are listed in Table 3. Bacteria were grown routinely in LB (10 g l^-1 of tryptone, 5 g l^-1 of yeast extract and 5 g l^-1 of NaCl). E. coli cells were grown at 37°C while P. putida was cultured at 30°C. Selection of P. putida cells was made onto M9 minimal medium plates [55 ] with citrate (2 g l^-1) as the sole carbon source. Antibiotics, when needed, were added at the following final concentration: ampicillin (Ap) 150 μg ml^-1 for E. coli and 500 μg ml^-1 for P. putida, kanamycin (Km) 50 μg ml^-1 and chloramphenicol (Cm) 30 μg ml^-1 for both species. 5-bromo-4-chloro-3-indolyl- β-D-galactopyranoside (Xgal) was added when required at 40 μg ml^-1. The Pu-lacZ fusion of P. putida MAD1 (Table 3) was induced by exposing cells to saturating m-xylene vapors.