Analysis of sucrose-induced small RNAs in Streptococcus mutans in the presence of different sucrose concentrations.

Streptococcus mutans (S. mutans) is the major pathogen contributing to dental caries. Sucrose is an important carbohydrate source for S. mutans and is crucial for dental caries. Small RNAs (sRNAs) are key post-transcriptional regulators of stress adaptation and virulence in bacteria. Here, for the first time, we created three replicate RNA libraries exposed to either 1 or 5% sucrose. The expression levels of sRNAs and target genes (gtfB, gtfC, and spaP) related to virulence were assessed. In addition, some phenotypic traits were evaluated. We obtained 2125 sRNA candidates with at least 100 average reads in 1% sucrose or 5% sucrose. Of these candidates, 2 were upregulated and 20 were downregulated in 1% sucrose. Six of these 22 differentially expressed sRNAs were validated by qRT-PCR. The expression level of target gene gtfB was higher in 1% sucrose. The adherence ratio of S. mutans was higher in 1% sucrose than in 5% sucrose. The synthesis of water-insoluble glucans (WIGs) was significantly higher in 5% sucrose than in 1% sucrose. These data suggest that a series of sRNAs can be induced in response to sucrose, and that some sRNAs might be involved in the regulation of phenotypes, providing new insight into the prevention of caries.

[Experimental study on the remediation of chromium contaminated groundwater with PRB media].

Due to the surface reaction between zero-valent iron and Cr(VI), iron cannot be fully utilized in the Fe(0)-Permeable Reactive Barrier(PRB), and the PRB is prone to compaction and blockage. In order to resolve these problems, iron powder coated with different polymer was tested in the treatment of chromium-polluted groundwater. Experimental results demonstrated that sodium alginate (SA) was the best package materials. According to analysis with FEI and EDX, pore structures were created by cross-linking of SA with Ca2+, in which a lot of attaching points exist, and through which Cr(VI) could react with interior iron powder. SA coating cast iron (SAC) and reduced iron (SAR) were tested in the treatment of chromium-polluted groundwater individually; the results showed that the removal efficiency of Cr( VI) by SAC was double that by SAR. After optimization of technology parameters of SAC, the Cr(VI) removal process follows the pseudo first-order kinetics. Based on dynamic experiments with SAC, Cr(VI)/Fe(0) was up to 32.25 mg x g(-1) and the PRB maintained high permeability coefficient (2.38 cm x s(-1)) after complete reaction. Compared with cast iron media is feasible in the remediation of chromium contaminated groundwater.