Streptococcus gordonii biofilm formation: Identification of genes that code for biofilm phenotypes

Viridans streptococci, which include Streptococcus gordonii, are pioneer or al bacteria that initiate dental plaque formation. Sessile bacteria in a bi ofilm exhibit a made of growth that is distinct from that of planktonic bac teria, Biofilm formation of S. gordonii Challis was characterized using an in vitro biofilm formation assay on polystyrene surfaces. The same assay wa s used as a nonbiased method to screen isogenic mutants generated by Tn916 transposon mutagenesis for defective biofilm formation. Biofilms formed opt imally when bacteria,were grown in a minimal medium under anaerobic conditi ons. Biofilm formation was affected by changes in pH, osmolarity; and carbo hydrate content of the growth media. Eighteen biofilm-defective mutants of S, gordonii Challis were identified based on Southern hybridization with a Tn916-based probe and DNA sequences of the Tn916-flanking regions. Molecula r analyses of these mutants shelved that some of the genes required for bio film formation are involved in signal transduction, peptidoglycan biosynthe sis, and adhesion. These characteristics are associated with quorum sensing , osmoadaptatian, and adhesion functions in oral streptococci. Only nine of the biofilm-defective mutants had defects in genes of known function, sugg esting that novel aspects of bacterial physiology may play a part in biofil m formation, Further identification and characterization of biofilm-associa ted genes will provide insight into the molecular mechanisms of biofilm for mation of oral streptococci.