title: Streptococcus mutans extracellular DNA is upregulated during growth in biofilms, actively released via membrane vesicles, and influenced by components of the protein secretion machinery.
abstract: Streptococcus mutans, a major etiological agent of human dental caries, lives primarily on the tooth surface in biofilms. Limited information is available concerning the extracellular DNA (eDNA) as a scaffolding matrix in S. mutans biofilms. This study demonstrates that S. mutans produces eDNA by multiple avenues, including lysis-independent membrane vesicles. Unlike eDNAs from cell lysis that were abundant and mainly concentrated around broken cells or cell debris with floating open ends, eDNAs produced via the lysis-independent pathway appeared scattered but in a structured network under scanning electron microscopy. Compared to eDNA production of planktonic cultures, eDNA production in 5- and 24-h biofilms was increased by >3- and >1.6-fold, respectively. The addition of DNase I to growth medium significantly reduced biofilm formation. In an in vitro adherence assay, added chromosomal DNA alone had a limited effect on S. mutans adherence to saliva-coated hydroxylapatite beads, but in conjunction with glucans synthesized using purified glucosyltransferase B, the adherence was significantly enhanced. Deletion of sortase A, the transpeptidase that covalently couples multiple surface-associated proteins to the cell wall peptidoglycan, significantly reduced eDNA in both planktonic and biofilm cultures. Sortase A deficiency did not have a significant effect on membrane vesicle production; however, the protein profile of the mutant membrane vesicles was significantly altered, including reduction of adhesin P1 and glucan-binding proteins B and C. Relative to the wild type, deficiency of protein secretion and membrane protein insertion machinery components, including Ffh, YidC1, and YidC2, also caused significant reductions in eDNA.
authors.affiliation: Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
authors.forename: Sumei
authors.initials: S
authors.lastname: Liao
authors.affiliation: Center for Oral Biology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
authors.forename: Marlise I
authors.initials: MI
authors.lastname: Klein
authors.affiliation: Department of Oral Biology, University of Florida School of Dentistry, Gainesville, Florida, USA.
authors.forename: Kyle P
authors.initials: KP
authors.lastname: Heim
authors.affiliation: Department of Comprehensive Dentistry and Biomaterials, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
authors.forename: Jacob P
authors.initials: JP
authors.lastname: Bitoun
authors.affiliation: Department of Oral Biology, University of Florida School of Dentistry, Gainesville, Florida, USA.
authors.forename: San-Joon
authors.initials: SJ
authors.lastname: Ahn
authors.affiliation: Department of Oral Biology, University of Florida School of Dentistry, Gainesville, Florida, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Burne
authors.affiliation: Department of Orthodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania, USA.
authors.forename: Hyun
authors.initials: H
authors.lastname: Koo
authors.affiliation: Department of Oral Biology, University of Florida School of Dentistry, Gainesville, Florida, USA.
authors.forename: L Jeannine
authors.initials: LJ
authors.lastname: Brady
authors.affiliation: Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA Department of Comprehensive Dentistry and Biomaterials, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA Department of Microbiology, Immunology, and Parasitology, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA zwen@lsuhsc.edu.
authors.forename: Zezhang T
authors.initials: ZT
authors.lastname: Wen
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D002462:Cell Membrane / Q000502:physiology*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D014176:Protein Biosynthesis / Q000502:physiology*; D013295:Streptococcus mutans / Q000235:genetics / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D015854:Up-Regulation
chemical_list: D004269:DNA, Bacterial
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