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In Pseudomonas aeruginosa PAO1, expression of elastase is dependent upon an interaction between the positive transcriptional activator LasR and the autoinducer molecule N(3‐oxododecanoyl)‐l‐homoserine lactone (OdDHL), the synthesis of which is directed by LasI. Previously we have shown that in PAN067, an elastase‐negative mutant of PAO1, elastase production can be restored to some extent by addition of exogenous N(3‐oxohexanoyl)‐l‐homoserine lactone (OHHL). Here we report that PAN067 is also defective in the production of alkaline protease, haemolysin, cyanide, pyocyanin and autoinducer(s). As neither addition of exogenous OdDHL nor introduction of IasR restored PAN067 to the parental phenotype, we sought to complement PAN067 with PAO1 DNA. From a cosmid library, a 2 kb DNA fragment was identified which re‐established production of autoinducer(s) and exoproducts in PAN067 …