FIG 5.

FimV TPR3 regulates type II secretion through modulation of cAMP levels. fimV and fimV cyaB-R456L strains were transformed with arabinose-inducible expression vectors encoding full-length FimV (FimV) or a truncation mutant lacking TPR3 (FimV₆₈₉). As controls, the strains were also transformed with empty vector (pB), and representative high cAMP (cyaB-R456L) and low cAMP (cyaAB) strains were included. Cells were grown overnight and resuspended in PBS at an OD₆₀₀ of 0.6. The, 2 μl of resuspended cells was spotted onto Trypticase soy broth–1.5% agar supplemented with 0.1% (wt/vol) arabinose and 2% (wt/vol) skim milk, followed by incubation for 40 h at 30°C. Elastase secretion was visualized as a zone of clearance around the bacterial colony. Secretion for each strain was measured as the difference between the diameter of the zone of clearance and the diameter of the colony (average for n = 3). The images are representative of three experiments. Scale bar, 1 cm.