Visualization of lipase activity in biofilms of P. aeruginosa. Membrane filter biofilms (PIA + Ca2+, 24 h, 36°C) of the parent strain P. aeruginosa SG81, the lipA overexpression strain SG81lipA+, the lipA defect mutant SG81ΔlipA and their corresponding complementation strain SG81ΔlipA::lipA were stained using the lipase substrate ELF®-97-palmitate. Shown are CLSM micrographs (optical section in the vertical middle of the biofilms) at a 400-fold magnification. For cell staining SYTO 9 (green) were used. Lipase activity, red; cells, green; overlay, yellow. The bars indicate 20 μm.