Distinct domains of CheA confer unique functions in chemotaxis and cell length in Azospirillum brasilense Sp7

Jessica M. Gullett, Amber Bible, Gladys Alexandre

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Chemotaxis is the movement of cells in response to gradients of diverse chemical cues. Motile bacteria utilize a conserved chemotaxis signal transduction system to bias their motility and navigate through a gradient. A central regulator of chemotaxis is the histidine kinase CheA. This cytoplasmic protein interacts with membrane-bound receptors, which assemble into large polar arrays, to propagate the signal. In the alphaproteobacterium Azospirillum brasilense, Che1 controls transient increases in swimming speed during chemotaxis, but it also biases the cell length at division. However, the exact underlying molecular mechanisms for Che1- dependent control of multiple cellular behaviors are not known. Here, we identify specific domains of the CheA1 histidine kinase implicated in modulating each of these functions. We show that CheA1 is produced in two isoforms: a membraneanchored isoform produced as a fusion with a conserved seven-transmembrane domain of unknown function (TMX) at the N terminus and a soluble isoform similar to prototypical CheA. Site-directed and deletion mutagenesis combined with behavioral assays confirm the role of CheA1 in chemotaxis and implicate the TMX domain in mediating changes in cell length. Fluorescence microscopy further reveals that the membrane-anchored isoform is distributed around the cell surface while the soluble isoform localizes at the cell poles. Together, the data provide a mechanism for the role of Che1 in controlling multiple unrelated cellular behaviors via acquisition of a new domain in CheA1 and production of distinct functional isoforms.

Original languageEnglish
Article numbere00189-17
JournalJournal of Bacteriology
Volume199
Issue number13
DOIs
StatePublished - Jul 1 2017

Funding

This work was supported by National Science Foundation (NSF) grants MCB-0919819 and MCB 1330344, awarded to G.A. We acknowledge support from the University of Tennessee College of Arts and Sciences and the BCMB department to attend the ASM Scientific Writing and Publishing Institute, which provided assistance with scientific writing development. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. We thank Anastasia Aksenova for valuable input and technical assistance. We declare no conflict of interest.

Keywords

  • Azospirillum
  • Chemotaxis
  • Signal transduction

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