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author:("Wang, lenke")
1.  Hyperosmotic response of streptococcus mutans: from microscopic physiology to transcriptomic profile 
BMC Microbiology  2013;13:275.
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.
doi:10.1186/1471-2180-13-275
PMCID: PMC4219374  PMID: 24289739
Streptococcus mutans; Hyperosmotic condition; Transcriptional profile; Biofilm dispersal; Environmental fitness; Dental plaque
2.  Molecular Characterization of the Microbiota Residing at the Apical Portion of Infected Root Canals of Human Teeth 
Journal of endodontics  2011;37(10):1359-1364.
Introduction
This study investigated the bacterial communities residing in the apical portion of human teeth with apical periodontitis in primary and secondary infections using a culture-independent molecular biology approach.
Methods
Root canal samples from the apical root segments of extracted teeth were collected from 18 teeth with necrotic pulp and 8 teeth with previous endodontic treatment. Samples were processed for amplification via polymerase chain reaction (PCR) and separated with denaturing gradient gel electrophoresis (DGGE). Selected bands were excised from the gel and sequenced for identification.
Results
Comparable to previous studies of entire root canals, the apical bacterial communities in primary infections were significantly more diverse than in secondary infections (p=0.0003). Inter- and intra-patient comparisons exhibited similar variations in profiles. Different roots of the same teeth with secondary infections displayed low similarity in bacterial composition, while an equivalent sample collected from primary infection contained almost identical populations. Sequencing revealed a high prevalence of fusobacteria, Actinomyces sp. and oral Anaeroglobus geminatus in both types of infection. Many secondary infections contained Burkholderiales or Pseudomonas sp. both of which represent opportunistic environmental pathogens.
Conclusion
Certain microorganisms exhibit similar prevalence in primary and secondary infection indicating that they are likely not eradicated during endodontic treatment. The presence of Burkholderiales and Pseudomonas sp. underscores the problem of environmental contamination. Treatment appears to affect the various root canals of multi-rooted teeth differently, resulting in local changes of the microbiota.
doi:10.1016/j.joen.2011.06.020
PMCID: PMC3415298  PMID: 21924182
Apical periodontitis; endodontic infections; community profiling; polymerase chain reaction; denaturing gradient gel electrophoresis
3.  The influence of iron availability on human salivary microbial community composition 
Microbial Ecology  2012;64(1):152-161.
It is a well-recognized fact that the composition of human salivary microbial community is greatly affected by its nutritional environment. However, most studies are currently focused on major carbon or nitrogen sources with limited attention to trace elements like essential mineral ions. In this study, we examined the effect of iron availability on the bacterial profiles of an in vitro human salivary microbial community as iron is an essential trace element for the survival and proliferation of virtually all microorganisms. Analysis via a combination of PCR with denaturing gradient gel electrophoresis (DGGE) demonstrated a drastic change in species composition of an in vitro human salivary microbiota when iron was scavenged from the culture medium by addition of the iron chelator 2,2’- bipyridyl (Bipy). This shift in community profile was prevented by the presence of excessive ferrous iron (Fe2+). Most interestingly, under iron deficiency, the in vitro grown salivary microbial community became dominated by several hemolytic bacterial species, including Streptococcus spp., Gemella spp. and Granulicatella spp.all of which have been implicated in infective endocarditis. These data provide evidence that iron availability can modulate host-associated oral microbial communities, resulting in a microbiota with potential clinical impact.
doi:10.1007/s00248-012-0013-2
PMCID: PMC3376180  PMID: 22318873
iron availability; microbial flora; oral cavity

Results 1-3 (3)