title: Bacillus subtilis Early Colonization of Arabidopsis thaliana Roots Involves Multiple Chemotaxis Receptors.
abstract: Colonization of plant roots by Bacillus subtilis is mutually beneficial to plants and bacteria. Plants can secrete up to 30% of their fixed carbon via root exudates, thereby feeding the bacteria, and in return the associated B. subtilis bacteria provide the plant with many growth-promoting traits. Formation of a biofilm on the root by matrix-producing B. subtilis is a well-established requirement for long-term colonization. However, we observed that cells start forming a biofilm only several hours after motile cells first settle on the plant. We also found that intact chemotaxis machinery is required for early root colonization by B. subtilis and for plant protection. Arabidopsis thaliana root exudates attract B. subtilis in vitro, an activity mediated by the two characterized chemoreceptors, McpB and McpC, as well as by the orphan receptor TlpC. Nonetheless, bacteria lacking these chemoreceptors are still able to colonize the root, suggesting that other chemoreceptors might also play a role in this process. These observations suggest that A. thaliana actively recruits B. subtilis through root-secreted molecules, and our results stress the important roles of B. subtilis chemoreceptors for efficient colonization of plants in natural environments. These results demonstrate a remarkable strategy adapted by beneficial rhizobacteria to utilize carbon-rich root exudates, which may facilitate rhizobacterial colonization and a mutualistic association with the host.
  
  
  
  Bacillus subtilis is a plant growth-promoting rhizobacterium that establishes robust interactions with roots. Many studies have now demonstrated that biofilm formation is required for long-term colonization. However, we observed that motile B. subtilis mediates the first contact with the roots. These cells differentiate into biofilm-producing cells only several hours after the bacteria first contact the root. Our study reveals that intact chemotaxis machinery is required for the bacteria to reach the root. Many, if not all, of the B. subtilis 10 chemoreceptors are involved in the interaction with the plant. These observations stress the importance of root-bacterium interactions in the B. subtilis lifestyle.
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Rosalie
authors.initials: R
authors.lastname: Allard-Massicotte
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Laurence
authors.initials: L
authors.lastname: Tessier
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Lécuyer
authors.affiliation: Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, USA.
authors.forename: Venkatachalam
authors.initials: V
authors.lastname: Lakshmanan
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Lucier
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Garneau
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Larissa
authors.initials: L
authors.lastname: Caudwell
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Hera
authors.initials: H
authors.lastname: Vlamakis
authors.affiliation: Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, USA.
authors.forename: Harsh P
authors.initials: HP
authors.lastname: Bais
authors.affiliation: Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada pascale.b.beauregard@usherbrooke.ca.
authors.forename: Pascale B
authors.initials: PB
authors.lastname: Beauregard
mesh_terms: D017360:Arabidopsis / Q000382:microbiology*; D001412:Bacillus subtilis / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism; D018441:Biofilms / Q000254:growth & development; D002633:Chemotaxis; D005122:Exudates and Transudates / Q000378:metabolism; D008124:Locomotion; D018517:Plant Roots / Q000382:microbiology*; D011956:Receptors, Cell Surface / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011956:Receptors, Cell Surface