title: The vascular plant-pathogenic bacterium Ralstonia solanacearum produces biofilms required for its virulence on the surfaces of tomato cells adjacent to intercellular spaces.
abstract: The mechanism of colonization of intercellular spaces by the soil-borne and vascular plant-pathogenic bacterium Ralstonia solanacearum strain OE1-1 after invasion into host plants remains unclear. To analyse the behaviour of OE1-1 cells in intercellular spaces, tomato leaves with the lower epidermis layers excised after infiltration with OE1-1 were observed under a scanning electron microscope. OE1-1 cells formed microcolonies on the surfaces of tomato cells adjacent to intercellular spaces, and then aggregated surrounded by an extracellular matrix, forming mature biofilm structures. Furthermore, OE1-1 cells produced mushroom-type biofilms when incubated in fluids of apoplasts including intercellular spaces, but not xylem fluids from tomato plants. This is the first report of biofilm formation by R. solanacearum on host plant cells after invasion into intercellular spaces and mushroom-type biofilms produced by R. solanacearum in vitro. Sugar application led to enhanced biofilm formation by OE1-1. Mutation of lecM encoding a lectin, RS-IIL, which reportedly exhibits affinity for these sugars, led to a significant decrease in biofilm formation. Colonization in intercellular spaces was significantly decreased in the lecM mutant, leading to a loss of virulence on tomato plants. Complementation of the lecM mutant with native lecM resulted in the recovery of mushroom-type biofilms and virulence on tomato plants. Together, our findings indicate that OE1-1 produces mature biofilms on the surfaces of tomato cells after invasion into intercellular spaces. RS-IIL may contribute to biofilm formation by OE1-1, which is required for OE1-1 virulence.
authors.affiliation: Laboratory of Plant Pathology and Biotechnology, Kochi University, Nankoku, Kochi 783-8502, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Mori
authors.affiliation: Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Kanako
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, Hyogo 657-8501, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Nakayashiki
authors.affiliation: Laboratory of Plant Pathology and Biotechnology, Kochi University, Nankoku, Kochi 783-8502, Japan.
authors.forename: Chikaki
authors.initials: C
authors.lastname: Higashimoto
authors.affiliation: Research Institute of Molecular Genetics, Kochi University, Nankoku, Kochi 783-8502, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Ohnishi
authors.affiliation: Laboratory of Plant Pathology and Biotechnology, Kochi University, Nankoku, Kochi 783-8502, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Kiba
authors.affiliation: Laboratory of Plant Pathology and Biotechnology, Kochi University, Nankoku, Kochi 783-8502, Japan.
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Hikichi
mesh_terms: D001422:Bacterial Adhesion / Q000187:drug effects; D018441:Biofilms; D001704:Biopolymers / Q000378:metabolism; D002241:Carbohydrates / Q000494:pharmacology; D015169:Colony Count, Microbial; D005110:Extracellular Space / Q000187:drug effects / Q000382:microbiology*; D018551:Solanum lycopersicum / Q000187:drug effects / Q000382:microbiology* / Q000648:ultrastructure; D009154:Mutation / Q000235:genetics; D058526:Plant Vascular Bundle / Q000187:drug effects / Q000382:microbiology*; D043368:Ralstonia solanacearum / Q000187:drug effects / Q000472:pathogenicity* / Q000648:ultrastructure; D014774:Virulence / Q000187:drug effects
chemical_list: D001704:Biopolymers; D002241:Carbohydrates
keywords: Ralstonia solanacearum; biofilm; intercellular spaces; lectin; soil-borne vascular plant-pathogenic bacterium; virulence