Motility of YB3558, YB3559 and ctrA401. The swarm assay was performed as described in the Methods. The non-motile rpoN mutant and the polar development mutant ΔpodJ are included. YB3558 displays an intermediate swarming defect, between ΔpodJ and wild-type levels, similar to a ctrA temperature sensitive lethal allele grown under permissive conditions. Complementation of YB3558 with a wild-type ctrA gene under native control (YB3559) does not restore the swarming phenotype.