Quantification of the Genetic Expression of bgl-A, bgl, and CspA and Enzymatic Characterization of β-Glucosidases from Shewanella sp. G5

Antimicrobial effects of the ginsenoside Rh2 on monospecies and multispecies cariogenic biofilms

AIMS

To investigate the effects of the ginsenoside Rh2 on monospecies and multispecies cariogenic biofilms and explore the mechanism of the antibiofilm effect of Rh2 in vitro.

METHODS AND RESULTS

Streptococcus mutans, Streptococcus sobrinus and Streptococcus sanguinis were chosen to form the monospecies or multispecies biofilms. Crystal violet staining and laser scanning confocal microscopy were used to observe the effect of Rh2 on biofilms in vitro. Cytotoxicity was examined by the Cell Counting Kit-8. The effects of Rh2 on bacterial membranes were observed via transmission electron microscopy (TEM). The isobaric tags for relative and absolute quantification (iTRAQ) method were used to profile the common differentially expressed proteins. Gene expression was analysed by reverse transcription quantitative polymerase chain reaction. In general, the treatment of cariogenic biofilms with Rh2 significantly decreased biomass accumulation by inhibiting bacterial growth and extracellular polysaccharide synthesis without any cytotoxic effects. TEM imaging showed that Rh2 could disrupt the cell membranes of these bacteria. The iTRAQ results indicated that the levels of mannose-specific IIC/D and acetaldehyde/alcohol dehydrogenase were substantially down-regulated, while the mRNA expression of the corresponding genes were significantly changed.

CONCLUSIONS

Our data revealed a potential application for Rh2 in the protection against dental caries via the inhibition of cariogenic biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study describes the first application of a ginsenoside against multispecies cariogenic biofilms. Rh2 may serve as an alternative agent to prevent dental caries by effectively modulating the pathogenic potentials of oral biofilms.

Complete genome sequence of the dissimilatory azo reducing thermophilic bacterium Novibacillus thermophiles SG-1

With the isolation and identification of efficient azo-dye degradation bacteria, bioaugmentation with specific microbial strains has now become an effective strategy to promote the bioremediation of azo dye. However, Azo dye wastewater discharged at high temperature restricted the extensive application of the known mesophilic azoreducing microorganisms. Here we present the complete genome sequence of a bacterium capable of reducing azo dye under thermophilic condition, Novibacillus thermophiles SG-1 (=KCTC 33118^T =CGMCC 1.12363^T). The complete genome of strain SG-1 contains a circular chromosome of 3,629,225 bp with a G + C content of 50.44%. Genome analysis revealed that strain SG-1 possessed genes encoding riboflavin biosynthesis protein that would secrete riboflavin, which could act as electron shuttles to transport the electrons to extracellular azo dye in decolorization process. HPLC analysis showed that the concentration of riboflavin increased from 0.01 μM to 0.255 μM with the growth of strain SG-1 under azo dye reduction. Quantitative real-time PCR analysis further demonstrated that the gene encoding riboflavin biosynthesis protein would be involved in the azo dye decolorization. The results from this study would be beneficial to research the mechanism of anaerobic reduction of azo dye under thermophilic conditions.