title: Hyperosmotic response of streptococcus mutans: from microscopic physiology to transcriptomic profile.
abstract: BACKGROUND
  Oral streptococci metabolize carbohydrate to produce organic acids, which not only decrease the environmental pH, but also increase osmolality of dental plaque fluid due to tooth demineralization and consequent calcium and phosphate accumulation. Despite these unfavorable environmental changes, the bacteria continue to thrive. The aim of this study was to obtain a global view on strategies taken by Streptococcus mutans to deal with physiologically relevant elevated osmolality, and perseveres within a cariogenic dental plaque.
  
  
  RESULTS
  We investigated phenotypic change of S. mutans biofilm upon hyperosmotic challenge. We found that the hyperosmotic condition was able to initiate S. mutans biofilm dispersal by reducing both microbial content and extracellular polysaccharides matrix. We then used whole-genome microarray with quantitative RT-PCR validation to systemically investigate the underlying molecular machineries of this bacterium in response to the hyperosmotic stimuli. Among those identified 40 deferentially regulated genes, down-regulation of gtfB and comC were believed to be responsible for the observed biofilm dispersal. Further analysis of microarray data showed significant up-regulation of genes and pathways involved in carbohydrate metabolism. Specific genes involved in heat shock response and acid tolerance were also upregulated, indicating potential cross-talk between hyperosmotic and other environmental stress.
  
  
  CONCLUSIONS
  Hyperosmotic condition induces significant stress response on S. mutans at both phenotypic and transcriptomic levels. In the meantime, it may take full advantage of these environmental stimuli to better fit the fluctuating environments within oral cavity, and thus emerges as numeric-predominant bacterium under cariogenic conditions.
authors.forename: Chengcheng
authors.initials: C
authors.lastname: Liu
authors.forename: Yulong
authors.initials: Y
authors.lastname: Niu
authors.forename: Xuedong
authors.initials: X
authors.lastname: Zhou
authors.forename: Keke
authors.initials: K
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Cheng
authors.forename: Mingyun
authors.initials: M
authors.lastname: Li
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Li
authors.forename: Renke
authors.initials: R
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China. nixux1982@hotmail.com.
authors.forename: Xin
authors.initials: X
authors.lastname: Xu
mesh_terms: D018441:Biofilms / Q000187:drug effects; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D009997:Osmotic Pressure; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013295:Streptococcus mutans / Q000187:drug effects* / Q000502:physiology*; D013312:Stress, Physiological
chemical_list: D011135:Polysaccharides, Bacterial