FIG. 3.

Phenotypic characteristics of P. fluorescens strain SS101, the massA mutant, the clpP mutant, clpP+pME6031 (empty-vector control), and clpP+pME6031-clpP. (A) Growth at 25°C. At each time point, the cell density was measured spectrophotometrically (600 nm), and the mean values for four replicates are given; the error bars represent the standard errors of the mean. (B) Surface tension of cell-free culture supernatant of strain SS101 and the different mutants shown in panel A. (C) Biofilm formation by strain SS101 and the different mutants in a polystyrene 96-well plate containing 200 μl growth medium; cells firmly attached to the walls of the wells were stained with crystal violet, and their density was quantified spectrophotometrically at 600 nm. The mean values of four replicates are given. For each of the mutants, asterisks indicate statistically significant (P < 0.05) differences relative to wild-type SS101. (D) Swarming motility of wild-type strain SS101 and mutants on soft (0.6% [wt/vol]) agar plates. Five microliters of washed overnight cultures of wild-type SS101 and mutants was spot inoculated in the center of a soft agar plate and incubated for 48 to 72 h at 25°C.