AUTHOR=Zhu Bin , Song Lei , Kong Xiangzhen , Macleod Lorna C. , Xu Ping 

TITLE=A Novel Regulator Modulates Glucan Production, Cell Aggregation and Biofilm Formation in Streptococcus sanguinis SK36

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01154

DOI=10.3389/fmicb.2018.01154

ISSN=1664-302X

ABSTRACT=<p><italic>Streptococcus sanguinis</italic> is an early colonizer of tooth surfaces and a key player in plaque biofilm development. However, the mechanism of biofilm formation of <italic>S. sanguinis</italic> is still unclear. Here, we showed that deletion of a transcription factor, <italic>brpL</italic>, promotes cell aggregation and biofilm formation in <italic>S. sanguinis</italic> SK36. Glucan, a polysaccharide synthesized from sucrose, was over-produced and aggregated in the biofilm of Δ<italic>brpL</italic>, which was necessary for better biofilm formation ability of Δ<italic>brpL</italic>. Quantitative RT-PCR demonstrated that <italic>gtfP</italic> was significantly up-regulated in Δ<italic>brpL</italic>, which increased the productions of water-insoluble and water-soluble glucans. The Δ<italic>brpL</italic>Δ<italic>gtfP</italic> double mutant decreased biofilm formation ability of Δ<italic>brpL</italic> to a level similar like that of Δ<italic>gtfP</italic>. Interestingly, the biofilm of Δ<italic>brpL</italic> 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 Δ<italic>brpL</italic> was mediated by activating the expression of <italic>ciaR</italic>, another <italic>gtfP</italic>-related biofilm formation regulator. Double deletion of <italic>brpL</italic> and <italic>ciaR</italic> decreased biofilm formation ability to the phenotype of a Δ<italic>ciaR</italic> mutant. Additionally, RNA sequencing elucidated a broad range of genes, related to carbohydrate metabolism and uptake, were activated in Δ<italic>brpL</italic>. SSA_0222, a gene involved in the phosphotransferase system, was dramatically up-regulated in Δ<italic>brpL</italic> and essential for <italic>S. sanguinis</italic> survival under our experimental conditions. In summary, <italic>brpL</italic> modulates glucan production, cell aggregation and biofilm formation by regulating the expression of <italic>ciaR</italic> in <italic>S. sanguinis</italic> SK36.</p>