title: Identification of a novel two-component system in Streptococcus gordonii V288 involved in biofilm formation.
abstract: Streptococcus gordonii is a pioneer colonizer of the teeth, contributing to the initiation of the oral biofilm called dental plaque. To identify genes that may be important in biofilm formation, a plasmid integration library of S. gordonii V288 was used. After screening for in vitro biofilm formation on polystyrene, a putative biofilm-defective mutant was isolated. In this mutant, pAK36 was inserted into a locus encoding a novel two-component system (bfr [biofilm formation related]) with two cotranscribed genes that form an operon. bfrA encodes a putative response regulator, while bfrB encodes a receptor histidine kinase. The bfr mutant and wild-type strain V288 showed similar growth rates in Todd-Hewitt broth (THB). A bfr-cat fusion strain was constructed. During growth in THB, the reporter activity (chloramphenicol acetyltransferase) was first detected in mid-log phase and reached a maximum in stationary phase, suggesting that transcription of bfr was growth stage dependent. After being harvested from THB, the bfr mutant adhered less effectively than did wild-type strain V288 to saliva-coated hydroxyapatite (sHA). To simulate pioneer colonization of teeth, S. gordonii V288 was incubated with sHA for 4 h in THB with 10% saliva to develop biofilms. RNA was isolated, and expression of bfrAB was estimated. In comparison to that of cells grown in suspension (free-growing cells), bfr mRNA expression by sessile cells on sHA was 1.8-fold greater and that by surrounding planktonic cells was 3.5-fold greater. Therefore, bfrAB is a novel two-component system regulated in association with S. gordonii biofilm formation in vitro.
authors.affiliation: Department of Oral Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Yongshu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yu
authors.initials: Y
authors.lastname: Lei
authors.forename: Ali
authors.initials: A
authors.lastname: Khammanivong
authors.forename: Mark C
authors.initials: MC
authors.lastname: Herzberg
mesh_terms: D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018441:Biofilms / Q000254:growth & development*; D017886:Durapatite; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D009876:Operon; D011137:Polystyrenes; D012463:Saliva / Q000382:microbiology; D015398:Signal Transduction; D013291:Streptococcus / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D011137:Polystyrenes; D017886:Durapatite