FIG 1.

Experimental device. A polycarbonate cell culture bottle filled with 20 ml of KB and inoculated with bacteria is placed on a fixed vertical stand. The device and associated cameras are maintained within a 28°C incubator. The flask is scanned vertically every 5 min with a 600-nm laser beam with a 1-mm section. Light passing through the flask is collected by a photodiode. To obtain a measurement of the optical density in the flask along a vertical profile, the laser and linked photodiode are coupled to a motorized device that ensures smooth vertical translation. Three cameras are located around the flask. The first (camera 1) obtains a side-view image of the liquid phase of the medium using bright-field illumination. The second (camera 2), also fixed perpendicular to the flask, monitors fluorescence associated with pyoverdin (excitation of 405/emission of 450 nm). The third (camera 3) is oriented with a 45° angle and captures growth at the ALI using bright-field illumination.