Streptococcus gordonii biofilm formation: identification of genes that code for biofilm phenotypes - PubMed (original) (raw)

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

C Y Loo et al. J Bacteriol. 2000 Mar.

Abstract

Viridans streptococci, which include Streptococcus gordonii, are pioneer oral bacteria that initiate dental plaque formation. Sessile bacteria in a biofilm exhibit a mode of growth that is distinct from that of planktonic bacteria. Biofilm formation of S. gordonii Challis was characterized using an in vitro biofilm formation assay on polystyrene surfaces. The same assay was used as a nonbiased method to screen isogenic mutants generated by Tn916 transposon mutagenesis for defective biofilm formation. Biofilms formed optimally when bacteria were grown in a minimal medium under anaerobic conditions. Biofilm formation was affected by changes in pH, osmolarity, and carbohydrate 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. Molecular analyses of these mutants showed that some of the genes required for biofilm formation are involved in signal transduction, peptidoglycan biosynthesis, and adhesion. These characteristics are associated with quorum sensing, osmoadaptation, and adhesion functions in oral streptococci. Only nine of the biofilm-defective mutants had defects in genes of known function, suggesting that novel aspects of bacterial physiology may play a part in biofilm formation. Further identification and characterization of biofilm-associated genes will provide insight into the molecular mechanisms of biofilm formation of oral streptococci.

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Figures

FIG. 1

FIG. 1

Bacterial growth and biofilm formation of S. gordonii Challis under different growth conditions. Bacteria were grown in either BM, BM without glucose, BM without CAA, THB, THB+YE, or TSB. Growth and biofilm formation were measured under aerobic (#) and anaerobic conditions. All assays were performed in triplicate, and mean values and standard deviations are shown.

FIG. 2

FIG. 2

Bacterial growth and biofilm formation of S. gordonii Challis in BM with different levels of osmolarity. The NaCl supplement in BM varied from 0 to 0.4 M. Assays were performed using BM and polystyrene plates under anaerobic conditions. A representative row of CV-stained microtiter plate wells is shown above the graph.

FIG. 3

FIG. 3

Bacterial growth and biofilm formation of various oral streptococci. Assays were performed using BM and polystyrene plates under anaerobic conditions.

FIG. 4

FIG. 4

SEM micrographs of S. gordonii Challis biofilm formation on uncoated and coated polystyrene surfaces. (A) Uncoated polystyrene; (B) laminin; (C) type IV collagen; (D) fibronectin. Magnification is shown by the bar (10 μm). Two different magnifications are shown for each surface (×1,000 for the upper images and ×3,000 for the lower images).

FIG. 5

FIG. 5

Bacterial growth and biofilm formation of wild-type S. gordonii Challis and biofilm-defective mutants. Assays were performed using BM and polystyrene plates under anaerobic conditions.

FIG. 6

FIG. 6

Southern hybridization of Hin_dIII-digested chromosomal DNAs from nine representative biofilm-defective mutants with a DIG-labeled pAM120 probe containing Tn_916. Lanes: 1, 8F9 mutant; 2, 1C1 mutant; 3, 11E5 mutant; 4, 11B4 mutant; 5, 15B3 mutant; 6, 9F8 mutant; 7, 29E5 mutant; 8, 4B3 mutant; 9, 13A12 mutant. DNA sizes are shown on the right.

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