Fig. 3.

P. aeruginosa colony appearance and PQS and C4HSL production by PA14ΔlasR grown in the presence of farnesol, hydrogen peroxide and the oxidative stress protectant NAC. (a) PA14 ΔlasR and ΔlasRrhlR : : TetR colonies were grown in the absence or presence of hydrogen peroxide and photographed after 48 h. Colonies were grown on agar plugs in a 96-well microtitre dish. (b) PA14ΔlasR grown as spotted colonies on agar plates containing vehicle alone, 250 μM farnesol, 10 mM NAC or the combination of 10 mM NAC and 250 μM farnesol. (c) PQS production by ΔlasR colonies grown for 14 h in the absence and presence of 5 and 10 mM NAC, 250 μM farnesol or the combination of 5 and 10 mM NAC and 250 μM farnesol. PQS production was determined by TLC analysis and PQS was identified by comparison with an authentic PQS standard (25 ng). (d) C4HSL levels were measured from ΔlasR colonies grown for 14 h in the absence and presence of 250 μM farnesol or farnesol with 10 mM NAC. Levels were determined by luciferase activity (RLU) generated by the reporter plasmid pSB536, which detects short-chain AHLs. The assay was validated using a titrated authentic C4HSL standard.