Streptococcus mutans is considered the primary etiological agent of human dental caries. Glucosyltransferases (Gtfs) from S. mutans play important roles in the formation of biofilm matrix and the development of cariogenic oral biofilm. Therefore, Gtfs are considered an important target to prevent the development of dental caries. However, the role of transcription factors in regulating gtf expression is not yet clear. Here, we identify a MarR (multiple antibiotic resistance regulator) family transcription factor named EpsR (exopolysaccharide synthesis regulator), which negatively regulates gtfB expression and exopolysaccharide (EPS) production in S. mutans. The epsR in-frame deletion strain grew slowly, aggregated more easily in the presence of dextran, and displayed different colony morphology and biofilm structure. Notably, epsR deletion resulted in altered 3-dimensional biofilm architecture, increased water-insoluble EPS production, and upregulated GtfB protein content and activity. In addition, global gene expression profiling revealed differences in the expression levels of 69 genes in which gtfB was markedly upregulated. The conserved DNA motif for EpsR binding was determined by electrophoretic mobility shift assay and DNase I footprinting assays. Moreover, analysis of β-galactosidase activity suggested that EpsR acted as a repressor and inhibited gtfB expression. Taken together, our findings indicate that EpsR is an important transcription factor that regulates gtfB expression and EPS production in S. mutans. These results add new aspects to the complexity of regulating the expression of genes involved in the cariogenicity of S. mutans, which might lead to novel strategies to prevent the formation of cariogenic biofilm that may favor diseases.
Low surface energy composite antifouling coatings prepared from carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) have good values for investigation of biofouling-related biological questions on marine biofilm. In order to deeply study the mechanism of antifouling on the surface of CNTs-PDMS coatings, it is necessary to investigate the structure of the microbial flora in the early biofilm on the coating surface. In the present study, the specific aim of this study was to investigate the structure differences of prokaryotic flora in biofilm samples at the early stage of biofouling through 16S rDNA based high-throughput DNA sequencing. By annotating high-throughput DNA sequencing results, this study identified dominant prokaryotic phyla and genera in biofilms of CNTs-PDMS coatings and identified significant differences in microbial composition and its dynamics among different coatings. Though the analysis of the Shannon index, Simpson index, Chao1 index and ACE index, coatings with better antifouling properties and antifouling properties have significant differences in community diversity and abundance, indicating different antifouling properties can affect the type and content of biofilm communities. According to the canonical correspondence analysis (CCA), time and temperature are more related to microbial community distribution, while the diameter and length of nanomaterials are less correlated. Through this study, the differences in microbial composition and content of prokaryotic communities, differences in diversity and abundance of sample communities, the differences between multiple samples and the correlation with important environmental factors were preliminarily analyzed, which laid a decent foundation for further research on the mechanism of anti-fouling on the surface of CNTs and PDMS coatings.
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