Abstract
Streptococcus sanguinis is an early colonizer of tooth surfaces and a key player in plaque biofilm development. However, the mechanism of biofilm formation of S. sanguinis is still unclear. Here, we showed that deletion of a transcription factor, brpL, promotes cell aggregation and biofilm formation in S. sanguinis SK36. Glucan, a polysaccharide synthesized from sucrose, was over-produced and aggregated in the biofilm of ΔbrpL, which was necessary for better biofilm formation ability of ΔbrpL. Quantitative RT-PCR demonstrated that gtfP was significantly up-regulated in ΔbrpL, which increased the productions of water-insoluble and water-soluble glucans. The ΔbrpLΔgtfP double mutant decreased biofilm formation ability of ΔbrpL to a level similar like that of ΔgtfP. Interestingly, the biofilm of ΔbrpL had an increased tolerance to ampicillin treatment, which might be due to better biofilm formation ability through the mechanisms of cellular and glucan aggregation. RNA sequencing and quantitative RT-PCR revealed the modulation of a group of genes in ΔbrpL was mediated by activating the expression of ciaR, another gtfP-related biofilm formation regulator. Double deletion of brpL and ciaR decreased biofilm formation ability to the phenotype of a ΔciaR mutant. Additionally, RNA sequencing elucidated a broad range of genes, related to carbohydrate metabolism and uptake, were activated in ΔbrpL. SSA_0222, a gene involved in the phosphotransferase system, was dramatically up-regulated in ΔbrpL and essential for S. sanguinis survival under our experimental conditions. In summary, brpL modulates glucan production, cell aggregation and biofilm formation by regulating the expression of ciaR in S. sanguinis SK36.
Highlights
Biofilms are structured, surface-associated communities of microorganisms, which attach to biotic and abiotic surfaces, leading to several acute and chronic health conditions in humans, such as periodontitis (Brouwer et al, 2016; Bergenfelz and Hakansson, 2017; Kreth et al, 2017)
All strains were grown in biofilm media (BM) media supplemented with 1% sucrose and biofilms examined using crystal violet (CV) staining
wild-type SK36 (WT) and brpL strains were grown in BM supplemented with 1% sucrose for 7.5 h
Summary
Surface-associated communities of microorganisms, which attach to biotic and abiotic surfaces, leading to several acute and chronic health conditions in humans, such as periodontitis (Brouwer et al, 2016; Bergenfelz and Hakansson, 2017; Kreth et al, 2017). BrpL Regulates Biofilm in S. sanguinis polymeric substances (EPS) that comprises of polysaccharides, proteins, nucleic acids, and lipids (Flemming and Wingender, 2010). It does not appear to play a direct role in oral disease, it has been reported that oral S. sanguinis is frequently the cause of infective endocarditis, a potentially fatal biofilm-associated disease (Bor et al, 2013; Crump et al, 2014). Individuals with damage to their heart valve, such as from a congenital heart condition, form ‘vegetation,’ fibrin-platelet complexes, in which the bacteria colonize causing infective endocarditis (Cahill and Prendergast, 2016)
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