FIG. 4.

Aggregation as assessed by phase-contrast microscopy (scale bars, 10 μm). (A) Aggregates observed after 2 h in N. meningitidis comP, pilT, pilT2, pilU, pilV, pilX, and pilZ mutants. The WT strain and a nonpiliated pilD mutant were included as positive and negative controls, respectively. Aggregates restored in double pilXT and pilZT mutants are also shown. (B) Aggregation kinetics in pilT2 and pilV mutants. The WT strain was included as a control. Pictures were taken at 0, 10, and 45 min.