Involvement of AtoSC two-component system in Escherichia coli flagellar regulon

The AtoSC two-component system in Escherichia coli is a key regulator of many physiological processes. We report here the contribution of AtoSC in E. coli motility and chemotaxis. AtoSC locus deletion in Δ atoSC cells renders cells not motile or responsive against any chemoattractant or repellent independently of the AtoSC inducer’s presence. AtoSC expression through plasmid complemented the Δ atoSC phenotype. Cells expressing either AtoS or AtoC demonstrated analogous motility and chemotactic phenotypes as Δ atoSC cells, independently of AtoSC inducer’s presence. Mutations of AtoC phosphate-acceptor sites diminished or abrogated E. coli chemotaxis. trAtoC, the AtoC constitutive active form which lacks its receiver domain, up-regulated E. coli motility. AtoSC enhanced the transcription of the flhDC and fliAZY operons and to a lesser extent of the flgBCDEFGHIJKL operon. The AtoSC-mediated regulation of motility and chemotactic response required also the expression of the CheAY system. The AtoSC inducers enhanced the AtoSC-mediated motility and chemotaxis. Acetoacetate or spermidine further promoted the responses of only AtoSC-expressing cells, while Ca 2+ demonstrated its effects independently of AtoSC. Histamine regulated bacterial chemotaxis only in atoSC + cells in a concentration-dependent manner while reversed the AtoSC-mediated effects when added at high concentrations. The trAtoC-controlled motility effects were enhanced by acetoacetate or spermidine, but not by histamine. These data reveal that AtoSC system regulates the motility and chemotaxis of E. coli , participating in the transcriptional induction of the main promoters of the chemotactic regulon and modifying the motility and chemotactic phenotypes in an induction-dependent mechanism.