title: Extracellular DNases of Ralstonia solanacearum modulate biofilms and facilitate bacterial wilt virulence.
abstract: Ralstonia solanacearum is a soil-borne vascular pathogen that colonizes plant xylem vessels, a flowing, low-nutrient habitat where biofilms could be adaptive. Ralstonia solanacearum forms biofilm in vitro, but it was not known if the pathogen benefits from biofilms during infection. Scanning electron microscopy revealed that during tomato infection, R. solanacearum forms biofilm-like masses in xylem vessels. These aggregates contain bacteria embedded in a matrix including chromatin-like fibres commonly observed in other bacterial biofilms. Chemical and enzymatic assays demonstrated that the bacterium releases extracellular DNA in culture and that DNA is an integral component of the biofilm matrix. An R. solanacearum mutant lacking the pathogen's two extracellular nucleases (exDNases) formed non-spreading colonies and abnormally thick biofilms in vitro. The biofilms formed by the exDNase mutant in planta contained more and thicker fibres. This mutant was also reduced in virulence on tomato plants and did not spread in tomato stems as well as the wild-type strain, suggesting that these exDNases facilitate biofilm maturation and bacterial dispersal. To our knowledge, this is the first demonstration that R. solanacearum forms biofilms in plant xylem vessels, and the first documentation that plant pathogens use DNases to modulate their biofilm structure for systemic spread and virulence.
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Tuan
authors.initials: T
authors.lastname: Minh Tran
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI, 53706, USA.|Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: April
authors.initials: A
authors.lastname: MacIntyre
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Devanshi
authors.initials: D
authors.lastname: Khokhani
authors.affiliation: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Martha
authors.initials: M
authors.lastname: Hawes
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Caitilyn
authors.initials: C
authors.lastname: Allen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D003851:Deoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D005110:Extracellular Space / Q000201:enzymology* / Q000235:genetics; D018551:Solanum lycopersicum / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology*; D043368:Ralstonia solanacearum / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D003851:Deoxyribonucleases