FIG 6.

(A) Detection of elastase in the extracellular medium. Shown is a Coomassie blue-stained gel of extracellular medium of different P. aeruginosa strains. LasB (or elastase) was observed at 33 kDa after 4, 6, and 24 h of growth at 37°C with aeration. Glucose and arabinose were added in the culture medium after 1 h 30 min of growth at a final concentration of 0.5%, allowing, respectively, repression or induction of the P_BAD promoter of pTS51 bearing qslA. In order to standardize the protein samples, the equivalent of 1 OD₆₀₀ unit was loaded. (B) Kinetics of proteolytic activity of elastase secreted by P. aeruginosa. Proteolysis of proteins contained in skim milk allowed formation of a halo all around the colonies of P. aeruginosa, depending on the quantity of elastase secreted. D40ZQ (PAO1 strain lacking all the xcp genes) and PA14 ΔxcpT were used as controls, showing that protease activity observed was massively dependent on this T2SS effector. Elastase activity was observed after 8, 10, 12, 14, 16, and 35 h of growth at 30°C.