Fig. 1.

Nalidixic acid disk tests and UV tests of wild type and insertion mutants. A. Overnight cultures of each strain in LB were diluted to an OD₅₆₀ of approximately 1.0 and 200 μL of the diluted cultures were added to 3.0 mL of top agar. The top agar mixture was then poured onto an LB plate containing X-gal at 60 μg/mL. Four circular glass fiber filters (GF/C; approximately 1 cm in diameter) were placed onto the cooled plate. A solution of nalidixic acid was then delivered to the filter disks (0, 2, 4 or 8 uL of a 5 mg/ml stock in 10 mM NaOH, corresponding to 0, 10, 20 or 40 μg), starting from the top left position and continuing clockwise on each plate. The plates were incubated overnight at 37°C and photographed the next morning. The strain name is given above each plate, along with the gene interrupted by the transposon in parentheses (except for parental JH39, which has no transposon, and W16, which has not been sequenced). B. Overnight cultures of each strain were spotted (8 μL) in duplicate onto LB plates containing X-gal at 60 μg/mL. After four hours of incubation at 37°C, half the plate was exposed to UV (52.5 J/m², from a General Electric G15T8 germicidal bulb) while the other half was protected with a sheet of cardboard. The plates were then wrapped in foil to protect them from light and incubated for an additional four hours at 37°C. The plates were then stored at 4°C and photographed the next day.