FIG. 7.

Influence of Fe-rich and Fe-limited spent culture supernatants on twitching motility under Fe-limiting (A) and Fe-replete (B) conditions. P. aeruginosa strains K1120 (RhIR⁺), K2590 (RhlI⁻), and K2873 (RhlR⁻) were inoculated onto Fe-limited (A) or Fe-replete (100 μM FeCl₃) (B) glucose minimal agar medium without (---) or with added (10% final concentration) spent culture supernatants from P. aeruginosa strains K1120 grown in Fe-rich (10 μM FeCl₃) glucose minimal medium (+ Fe/K1120), K1120 grown in Fe-limited glucose minimal medium (− Fe/K1120), and K2590 grown in Fe-limited glucose minimal medium (− Fe/K2590) as indicated. Following incubation at 37°C for 40 h, the twitching zones were stained and their diameters measured. Results shown represent the means ± standard deviations for a representative assay (16 individual twitching zones measured per strain and/or growth conditions on two separate plates) performed in duplicate. Results for RhlIR⁺ K2589 were indistinguishable from those for K1120 and are not shown.