C12-3-oxo-AHL measurement produced by P. putida WCS358, by lon protease mutant derivative P. putida IBE4 and lon mutant containing a plasmid expressing the Lon protease, P. putida IBE4 (pBBRlon). C12-3-oxo-AHL was extracted from spent supernatants, AHL levels were measured with P. putida SM17 (prsaL220) with a volume of extract corresponding to an amount of 5 × 108 cfu as described in the Methods section. C12-3-oxo-AHL levels are proportional to β-galactosidase activity (Miller Units). Standard deviation bars are given on the mean value of three independent cultures. Statistical analysis was performed with Anova resulting in a significant main effect of the mutation with F(2,12) = 20.45 and p < .001. The same measurement was also performed using 1 μM of synthetic C12-3-oxo-AHL (obtained from P. Williams, University of Nottingham, UK).