title: Azospirillum brasilense Chemotaxis Depends on Two Signaling Pathways Regulating Distinct Motility Parameters.
abstract: The genomes of most motile bacteria encode two or more chemotaxis (Che) systems, but their functions have been characterized in only a few model systems. Azospirillum brasilense is a motile soil alphaproteobacterium able to colonize the rhizosphere of cereals. In response to an attractant, motile A. brasilense cells transiently increase swimming speed and suppress reversals. The Che1 chemotaxis pathway was previously shown to regulate changes in the swimming speed, but it has a minor role in chemotaxis and root surface colonization. Here, we show that a second chemotaxis system, named Che4, regulates the probability of swimming reversals and is the major signaling pathway for chemotaxis and wheat root surface colonization. Experimental evidence indicates that Che1 and Che4 are functionally linked to coordinate changes in the swimming motility pattern in response to attractants. The effect of Che1 on swimming speed is shown to enhance the aerotactic response of A. brasilense in gradients, likely providing the cells with a competitive advantage in the rhizosphere. Together, the results illustrate a novel mechanism by which motile bacteria utilize two chemotaxis pathways regulating distinct motility parameters to alter movement in gradients and enhance the chemotactic advantage.
  
  
  
  Chemotaxis provides motile bacteria with a competitive advantage in the colonization of diverse niches and is a function enriched in rhizosphere bacterial communities, with most species possessing at least two chemotaxis systems. Here, we identify the mechanism by which cells may derive a significant chemotactic advantage using two chemotaxis pathways that ultimately regulate distinct motility parameters.
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Tanmoy
authors.initials: T
authors.lastname: Mukherjee
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Dhivya
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Burriss
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA.|Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong, People's Republic of China.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Xie
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee, USA galexan2@utk.edu.
authors.forename: Gladys
authors.identifier: http://orcid.org/0000-0002-9238-4640
authors.initials: G
authors.lastname: Alexandre
mesh_terms: D015806:Azospirillum brasilense / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002633:Chemotaxis; D018517:Plant Roots / Q000382:microbiology; D015398:Signal Transduction; D014908:Triticum / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins