title: An Electrostatic Net Model for the Role of Extracellular DNA in Biofilm Formation by Staphylococcus aureus.
abstract: Staphylococcus aureus is an important human pathogen that can form biofilms on various surfaces. These cell communities are protected from the environment by a self-produced extracellular matrix composed of proteins, DNA, and polysaccharide. The exact compositions and roles of the different components are not fully understood. In this study, we investigated the role of extracellular DNA (eDNA) and its interaction with the recently identified cytoplasmic proteins that have a moonlighting role in the biofilm matrix. These matrix proteins associate with the cell surface upon the drop in pH that naturally occurs during biofilm formation, and we found here that this association is independent of eDNA. Conversely, the association of eDNA with the matrix was dependent on matrix proteins. Both proteinase and DNase treatments severely reduced clumping of resuspended biofilms; highlighting the importance of both proteins and eDNA in connecting cells together. By adding an excess of exogenous DNA to DNase-treated biofilm, clumping was partially restored, confirming the crucial role of eDNA in the interconnection of cells. On the basis of our results, we propose that eDNA acts as an electrostatic net, interconnecting cells surrounded by positively charged matrix proteins at a low pH.
  
  
  OBJECTIVE
  Extracellular DNA (eDNA) is an important component of the biofilm matrix of diverse bacteria, but its role in biofilm formation is not well understood. Here we report that in Staphylococcus aureus, eDNA associates with cells in a manner that depends on matrix proteins and that eDNA is required to link cells together in the biofilm. These results confirm previous studies that showed that eDNA is an important component of the S. aureus biofilm matrix and also suggest that eDNA acts as an electrostatic net that tethers cells together via the proteinaceous layer of the biofilm matrix.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Vanina
authors.initials: V
authors.lastname: Dengler
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Lucy
authors.initials: L
authors.lastname: Foulston
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Alicia S
authors.initials: AS
authors.lastname: DeFrancesco
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA losick@mcb.harvard.edu.
authors.forename: Richard
authors.initials: R
authors.lastname: Losick
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D013211:Staphylococcus aureus / Q000378:metabolism*; D055672:Static Electricity
chemical_list: D004269:DNA, Bacterial; D016326:Extracellular Matrix Proteins