title: Influence of calcium in extracellular DNA mediated bacterial aggregation and biofilm formation.
abstract: Calcium (Ca(2+)) has an important structural role in guaranteeing the integrity of the outer lipopolysaccharide layer and cell walls of bacterial cells. Extracellular DNA (eDNA) being part of the slimy matrix produced by bacteria promotes biofilm formation through enhanced structural integrity of the matrix. Here, the concurrent role of Ca(2+) and eDNA in mediating bacterial aggregation and biofilm formation was studied for the first time using a variety of bacterial strains and the thermodynamics of DNA to Ca(2+) binding. It was found that the eDNA concentrations under both planktonic and biofilm growth conditions were different among bacterial strains. Whilst Ca(2+) had no influence on eDNA release, presence of eDNA by itself favours bacterial aggregation via attractive acid-base interactions in addition, its binding with Ca(2+) at biologically relevant concentrations was shown further increase in bacterial aggregation via cationic bridging. Negative Gibbs free energy (ΔG) values in iTC data confirmed that the interaction between DNA and Ca(2+) is thermodynamically favourable and that the binding process is spontaneous and exothermic owing to its highly negative enthalpy. Removal of eDNA through DNase I treatment revealed that Ca(2+) alone did not enhance cell aggregation and biofilm formation. This discovery signifies the importance of eDNA and concludes that existence of eDNA on bacterial cell surfaces is a key facilitator in binding of Ca(2+) to eDNA thereby mediating bacterial aggregation and biofilm formation.
authors.affiliation: Centre for Marine BioInnovation, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Theerthankar
authors.initials: T
authors.lastname: Das
authors.affiliation: Centre for Marine BioInnovation, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia; Department of Microbiology, Quaid-i-Azam University, Islamabad, Pakistan.
authors.forename: Shama
authors.initials: S
authors.lastname: Sehar
authors.affiliation: Centre for Marine BioInnovation, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Leena
authors.initials: L
authors.lastname: Koop
authors.affiliation: Centre for Marine BioInnovation, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Yie Kuan
authors.initials: YK
authors.lastname: Wong
authors.affiliation: Department of Microbiology, Quaid-i-Azam University, Islamabad, Pakistan.
authors.forename: Safia
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Khawar Sohail
authors.initials: KS
authors.lastname: Siddiqui
authors.affiliation: Centre for Marine BioInnovation, School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Mike
authors.initials: M
authors.lastname: Manefield
mesh_terms: D001419:Bacteria / Q000166:cytology* / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D002118:Calcium / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D010933:Plankton / Q000187:drug effects / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000166:cytology / Q000187:drug effects; D013816:Thermodynamics
chemical_list: D004247:DNA; D003850:Deoxyribonuclease I; D002118:Calcium