FIG. 2.
UV-irradiated L. pneumophila expresses elevated levels of the competence gene comEA. The JR32 strain bearing the comEA-gfp reporter plasmid was exposed to increasing doses of 254-nm UV radiation (0, 2.5, 5.0, 7.5, and 10 J/m2) and then inoculated into rich medium in microtiter plates at low (A600 = 0.02, equivalent to OD600 = 0.1 [A and B]) or high (A600 = 0.2, equivalent to OD600 = 0.1 [C and D]) cell densities. Bacterial growth (A600 [A and C]) and comEA-gfp expression relative to cell density (GFP/OD, arbitrary units [B and D]) were measured every 10 min over a 24-h period. (E) Microscopic observation of individual L. pneumophila cells after exposure to UV radiation and norfloxacin. The JR32 strain bearing the comEA-gfp reporter plasmid was treated with a single dose of UV radiation (7.5 J/m2) or with a chronic exposure to norfloxacin. After a 24-h growth period, the bacteria were observed using white-light microscopy (top row) and fluorescence microscopy (bottom row). All photographs were taken with the same exposure time.