LIAS and cystic fibrosis: Inactivation of either las or rhl QS does not significantly affect the growth of PAO1 under phosphate limiting conditions (Fig. 3A) except for a slight lag in ΔrhlI. It has been reported that the rhl system can work independently of las regulation through the observation that LasRI null mutants are frequently isolated from CF patients29,39,47.To assess if these systems can work independently, we examined the gene expression of QS regulatory and virulence associated genes using the PAO1 QS mutants.