Arch Microbiol (2009) 191:501–507 DOI 10.1007/s00203-009-0475-x 123 ORIGINAL PAPER Characterization of chsA, a new gene controlling the chemotactic response in Azospirillum brasilense Sp7 Ricardo Carreño-López · Araceli Sánchez · Nohemí Camargo · Claudine Elmerich · Beatriz Eugenia Baca Received: 16 September 2008 / Revised: 7 March 2009 / Accepted: 27 March 2009 / Published online: 24 April 2009  Springer-Verlag 2009 Abstract We report, here, the characterization of a mutant strain of Azospirillum brasilense Sp7 impaired in surface motility and chemotactic response. Presence of Xagella in the mutant strain was conWrmed by western blot analysis, using antisera raised against the polar and lateral Xagellins, and by electron microscopy. Genetic comple- mentation and nucleotide sequencing led to the identiWca- tion of a new gene, named chsA. The deduced translation product, ChsA protein, contained a PAS sensory domain and an EAL domain. As ChsA displayed characteristic sig- naling protein architecture, it is thought that this protein is a component of the signaling pathway controlling chemo- taxis in Azospirillum. Keywords Azospirillum brasilense · ChsA signaling protein · Chemotactic response Introduction Azospirillum brasilense, a nitrogen-Wxing -proteobacte- rium promotes growth of various grasses and cereals (Dobbelaere et al. 2001). The bacterium possesses a single polar Xagellum and multiple lateral Xagella. The polar Xagellum is responsible for the swimming motility in liq- uid media, whereas the lateral Xagella are responsible for surface motility also referred to as swarming motility (Hall and Krieg 1983; Moens et al. 1995). A. brasilense exhibits chemotaxis toward a variety of oxidizable sub- strates including sugars, amino acids and organic acids, oxygen, and redox molecules (Alexandre et al. 2000; Barak et al. 1983). Non-Xagellated mutants as well as a mutant strain impaired in chemotactic response showed reduced colonization of the root system suggesting that active movement of Azospirillum is important for the ini- tiation of root colonization (Vande Broek et al. 1998). Several of the che genes encoding central transduction pathways in chemotaxis in other bacterial species (cheA, -W, -Y, -B and -R) were identiWed in Azospirillum (Hauwa- erts et al. 2002; Bible et al. 2008). Evidence for the exis- tence of a putative methyl-accepting chemotaxis protein (Potrich et al. 2001), as well as the identiWcation of a che- moreceptor-like protein (Tlp1), which mediates energy taxis in A. brasilense was also reported (Greer-Phillips et al. 2004). The present study reports the genetic characterization of a mutant strain impaired in surface motility and chemotaxis. This led to the identi Wcation of chsA, diVer- ent from genes previously characterized as being involved in chemotaxis in Azospirillum. The ChsA deduced translation product contains a sensory PAS domain and an EAL domain suggesting it may be part of the signaling pathway controlling chemotaxis in Azospirillum. An abstract of this work presented at the 15th Interna- tional nitrogen-Wxation conference has been published in the conference proceedings book (Carreño-López et al. 2008). Communicated by Ursula Priefer. R. Carreño-López · A. Sánchez · N. Camargo · B. E. Baca (&) Centro de Investigaciones en Ciencias Microbiológicas, Benemérita Universidad Autónoma de Puebla, 72000 Puebla, Mexico e-mail: ebaca@siu.buap.mx C. Elmerich Département de Microbiologie, BMGE, Institut Pasteur, Paris, France