FIG. 8.
Bioassay of C4-HSL production by P. aeruginosa during growth under Fe-limited and Fe-replete conditions. Aliquots (500 μl) of cell-free spent culture supernatants of P. aeruginosa K1120 (RhlI+) and K2590 (RhlI−) grown overnight in Fe-limited (− Fe/K1120 and − Fe/K2590) or Fe-replete (100 μM FeCl3) (+ Fe/K1120 and + Fe/K2590) glucose minimal medium were incubated with E. coli harboring the C4-HSL-responsive rhlA-lacZ fusion plasmid. After 6 h of incubation at room temperature, E. coli was assayed for β-galactosidase activity (reporter in Miller units [MU]) as an indirect measure of C4-HSL. The values shown represent the means ± standard deviations for two independent experiments performed in duplicate and are normalized to 1 ml of supernatant from a culture with an A600 of 1.