title: Trk2 Potassium Transport System in Streptococcus mutans and Its Role in Potassium Homeostasis, Biofilm Formation, and Stress Tolerance.
abstract: Potassium (K(+)) is the most abundant cation in the fluids of dental biofilm. The biochemical and biophysical functions of K(+) and a variety of K(+) transport systems have been studied for most pathogenic bacteria but not for oral pathogens. In this study, we establish the modes of K(+) acquisition in Streptococcus mutans and the importance of K(+) homeostasis for its virulence attributes. The S. mutans genome harbors four putative K(+) transport systems that included two Trk-like transporters (designated Trk1 and Trk2), one glutamate/K(+) cotransporter (GlnQHMP), and a channel-like K(+) transport system (Kch). Mutants lacking Trk2 had significantly impaired growth, acidogenicity, aciduricity, and biofilm formation. [K(+)] less than 5 mM eliminated biofilm formation in S. mutans. The functionality of the Trk2 system was confirmed by complementing an Escherichia coli TK2420 mutant strain, which resulted in significant K(+) accumulation, improved growth, and survival under stress. Taken together, these results suggest that Trk2 is the main facet of the K(+)-dependent cellular response of S. mutans to environment stresses.
  
  
  OBJECTIVE
  Biofilm formation and stress tolerance are important virulence properties of caries-causing Streptococcus mutans. To limit these properties of this bacterium, it is imperative to understand its survival mechanisms. Potassium is the most abundant cation in dental plaque, the natural environment of S. mutans. K(+) is known to function in stress tolerance, and bacteria have specialized mechanisms for its uptake. However, there are no reports to identify or characterize specific K(+) transporters in S. mutans. We identified the most important system for K(+) homeostasis and its role in the biofilm formation, stress tolerance, and growth. We also show the requirement of environmental K(+) for the activity of biofilm-forming enzymes, which explains why such high levels of K(+) would favor biofilm formation.
authors.affiliation: Department of Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Gursonika
authors.initials: G
authors.lastname: Binepal
authors.affiliation: Department of Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kamal
authors.initials: K
authors.lastname: Gill
authors.affiliation: Department of Oral Biology, University of Florida, Gainesville, Florida, USA.
authors.forename: Paula
authors.initials: P
authors.lastname: Crowley
authors.affiliation: Department of Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Martha
authors.initials: M
authors.lastname: Cordova
authors.affiliation: Department of Oral Biology, University of Florida, Gainesville, Florida, USA.
authors.forename: L Jeannine
authors.initials: LJ
authors.lastname: Brady
authors.affiliation: Department of Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Dilani B
authors.initials: DB
authors.lastname: Senadheera
authors.affiliation: Department of Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada d.cvitkovitch@dentistry.utoronto.ca.
authors.forename: Dennis G
authors.initials: DG
authors.lastname: Cvitkovitch
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D064587:Osmoregulation / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D013295:Streptococcus mutans / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D008565:Membrane Proteins; D011188:Potassium
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