Tsr or Tar alone supports swarming in E. coli. (A) Swarming motility is observed in wild-type (RP437) bacteria (a), but not in RP437 lacking all four transducers (HCB429) (b). Plasmids expressing Tsr (pJC3) (c) or Tar (pNT201) (d), but not those expressing Trg (pLA1) (e) or Tap (pCG1) (f), restore swarming in HCB429. (B) Swimming motility in the same strains as in A. As described in Methods, 20 μM IPTG was used to induce protein expression from plasmids. Plates in A were incubated for 16 h, whereas those in B were incubated for 12 h at 30°C.