FIG. 3.

Mutation in fliL results in cells that are locked into an elongated morphotype. The morphology of the wild-type (wt) and fliL (fliL) strains was examined by phase-contrast light microscopy after incubation (8 h at 37°C) in LB broth and on L agar. Wild-type cells differentiated to the swarmer cell morphotype when grown on L agar but not in LB broth (left column). In contrast, the FliL-defective strain differentiated into elongated cells, reminiscent of wild-type swarmer cells but lacking flagella, in liquid medium (LB broth; right top micrograph), a condition that does not induce differentiation in the wild type. The FliL⁻ strain also produced elongated cells that were significantly longer than wild-type swarmer cells (mean FliL⁻ cell length = 69.3 ± 10 μm versus 45.3 ± 9.1 μm for wild-type cells) when grown on agar-gelled LB. Bars = 25 μm.