Cariogenic virulence factors of Streptococcus mutans include acidogenicity, aciduricity, and extracellular polysaccharides (EPS) synthesis. The de novo designed antimicrobial peptide GH12 has shown bactericidal effects on S. mutans, but its interaction with virulence and regulatory systems of S. mutans remains to be elucidated. The objectives were to investigate the effects of GH12 on virulence factors of S. mutans, and further explore the function mechanisms at enzymatic and transcriptional levels. To avoid decrease in bacterial viability, we limited GH12 to subinhibitory levels. We evaluated effects of GH12 on acidogenicity of S. mutans by pH drop, lactic acid measurement and lactate dehydrogenase (LDH) assay, on aciduricity through survival rate at pH 5.0 and F1F0-ATPase assay, and on EPS synthesis using quantitative measurement, morphology observation, vertical distribution analyses and biomass calculation. Afterwards, we conducted quantitative real-time PCR to acquire the expression profile of related genes. GH12 at 1/2 MIC (4 mg/L) inhibited acid production, survival rate, EPS synthesis, and biofilm formation. The enzymatic activity of LDH and F1F0-ATPase was inhibited, and ldh, gtfBCD, vicR, liaR, and comDE genes were significantly downregulated. In conclusion, GH12 inhibited virulence factors of S. mutans, through reducing the activity of related enzymes, downregulating virulence genes, and inactivating specific regulatory systems.

Low-cost anthracite was used as the raw material for preparing microporosity controlled activated carbons by KOH activation. The adsorption characteristics of methane onto activated carbon were measured at 298 K and pressures up to 3.5 MPa by a volumetric method. The experimental data were fitted to the Dubinin–Astakhov model, and relative deviations of better than 0.1 % were obtained. Three main factors were suggested, accounting for the higher methane uptake. It was revealed that better methane uptake is dependent on larger micropore volume and specific surface area. When the micropore volume and surface area of two samples are similar, the activated carbon possessing a narrower micropore size distribution performed higher methane uptake. The relationship between the surface coverage (C/C 0) and the isosteric heat of adsorption confirmed that the heterogeneities of the as-obtained samples was a main factor influencing the methane adsorption at a surface coverage lower than 0.7. The activated carbon possessing higher heterogeneity deserved better methane uptake. The kinetics of methane adsorption on five activated carbons obeyed the pseudosecond-order equation very well under current experimental conditions (298 K, 0.28 MPa). The activated carbon displayed a faster adsorption rate and possessed a better adsorption capacity of methane.

A new self-propagated flaming (SPF) technique was applied to the synthesis of highly active layered CuO-δ-MnO hybrid composites, for the de-polluting catalytic total oxidation of gaseous toluene vapor. Other transition metal oxide-doped MnO hybrid composites were also successfully prepared and investigated, ensuring a feasible strategy for the fabrication of various layered MO-δ-MnO (M═Co, Ni, or Zn) hybrids. By changing the molar ratio of the precursors (KMnO and acetate salt) and the type of transition metal oxide introduced, it is possible to control the crystal structure and reducibility of the sheetlike hybrid composites as well as the catalytic activity for the total oxidation of toluene. The catalyst sample (CuO-δ-MnO) with a Mn/Cu molar ratio of 10:1 exhibited the highest catalytic performance, with a lower reaction temperature of 300 °C for complete toluene removal, which was comparable to the reaction temperature for total toluene conversion by the Pt-based catalyst. The SPF technique provides an approach for developing highly efficient catalysts for the complete removal of volatile organic compounds, by allowing the facile and energy-saving fabrication of large quantities of layered CuO-δ-MnO hybrids.

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