Enzymatic properties and degradation characterization of a bis(2-hydroxyethyl) terephthalate hydrolase from Saccharothrix sp / 生物工程学报

The discovery of new enzymes for poly(ethylene terephthalate) (PET) degradation has been a hot topic of research globally. Bis-(2-hydroxyethyl) terephthalate (BHET) is an intermediate compound in the degradation of PET and competes with PET for the substrate binding site of the PET-degrading enzyme, thereby inhibiting further degradation of PET. Discovery of new BHET degradation enzymes may contribute to improving the degradation efficiency of PET. In this paper, we discovered a hydrolase gene sle (ID: CP064192.1, 5085270-5086049) from Saccharothrix luteola, which can hydrolyze BHET into mono-(2-hydroxyethyl) terephthalate (MHET) and terephthalic acid (TPA). BHET hydrolase (Sle) was heterologously expressed in Escherichia coli using a recombinant plasmid, and the highest protein expression was achieved at a final concentration of 0.4 mmol/L of isopropyl-β-d-thiogalactoside (IPTG), an induction duration of 12 h and an induction temperature of 20 ℃. The recombinant Sle was purified by nickel affinity chromatography, anion exchange chromatography, and gel filtration chromatography, and its enzymatic properties were also characterized. The optimum temperature and pH of Sle were 35 ℃ and 8.0, and more than 80% of the enzyme activity could be maintained in the range of 25-35 ℃ and pH 7.0-9.0 and Co2+ could improve the enzyme activity. Sle belongs to the dienelactone hydrolase (DLH) superfamily and possesses the typical catalytic triad of the family, and the predicted catalytic sites are S129, D175, and H207. Finally, the enzyme was identified as a BHET degrading enzyme by high performance liquid chromatography (HPLC). This study provides a new enzyme resource for the efficient enzymatic degradation of PET plastics.

Effect of Sealant Application and Thermal Cycling on Bond Strength of Tissue Conditioners to Acrylic Resin

The aim of this study was to evaluate the effect of sealer application and thermal cycling on the bond strength between tissue conditioners and acrylic resin, and to observe the type of bond failure. Two hundred eighty-eight specimens (10x16x3 mm) were made of an acrylic resin (Lucitone 500, Dentsply) using a metal muffle. Specimens were divided into four groups according to the tissue conditioner (Coe-Comfort, GC or Dentusoft, Densell) used and whether or not a sealer (Eversoft Soft Liner Sealer, Myerson) was applied. Each of the four groups was subdivided into other six subgroups (n=12) to undergo thermocycling for 45, 90, 135, 180 or 210 cycles with a dwell time of 60 s, or to be left non thermocycled (control). Tensile bond strength was measured in a universal testing machine at a crosshead speed of 5 mm/min. Sealant application had no effect on the tensile bond strength of the relined acrylic resin, regardless of the tissue conditioner used (Coe-Comfort: p=0.306 and Dentusoft: p=0.1501). The number of thermal cycles had a significant effect on the tensile bond strength of the relined acrylic resin (Coe-Comfort: p=0.002 and Dentusoft: p<0.001). Both tissue conditioners presented similar bond strength to acrylic resin. For both tissue conditioners, sealer coatings had no influence on bond strength, while different numbers of thermal cycles affected that mechanical property.

Os objetivos deste estudo foram avaliar o efeito da aplicação de selante e a ciclagem térmica na resistência de união entre condicionadores de tecido e resina acrílica e observar o padrão de fratura. Duzentos e oitenta e oito espécimes (10×16×3 mm) de resina acrílica (Lucitone 500, Dentsply) foram confeccionados utilizando-se uma mufla metálica. Os espécimens foram divididos em quatro grupos de acordo com o condicionador de tecido (Coe-Comfort, GC ou Dentusoft, Densell) e com o uso ou não de selante (Eversoft Soft Liner Sealer, Myerson). Cada um dos quatro grupos foi subdividido em seis grupos para a realização de 45, 90, 135, 180 ou 210 ciclos térmicos, ou ausência de termociclagem (controle). Resistência de união por tração foi mensurada em uma máquina universal de ensaios com velocidade de 5 mm/min. A aplicação de selante não afetou a resistência de união por tração da resina acrílica reembasada, independentemente do condicionador de tecido utilizado (Coe-Comfort: p=0,306 e Dentusoft: p=0,1501). O número de ciclos térmicos apresentou efeito significativo na resistência de união por tração da resina acrílica reembasada (Coe-Comfort: p=0,002 e Dentusoft: p<0,001). Ambos os condicionadores de tecidos apresentaram resistência de união semelhante à resina acrílica. Para ambos os condicionadores de tecidos, a aplicação de selante não apresentou influência na resistência de união, enquanto que diferentes números de ciclos térmicos afetaram essa propriedade mecânica.

The effectiveness of magnesium oxide combined with tissue conditioners in inhibiting the growth of Candida albicans: An in vitro study.

Context : The presence of Candida albicans on the fitting surface of the denture is a major causative factor in denture stomatits. A treatment method is by combining tissue conditioner and antifungal agents. Aims : The main objective of this study is to test the efficacy of magnesium oxide combined with two tissue conditioners (Viscogel and GC Soft), in inhibiting the growth of Candida albicans. Settings and Design : Microbiological study was done in the Department of Microbiology, K S Hegde Medical Academy, Nitte University, Mangalore. Materials and Methods : A total of 154 plates were prepared using Muller Hilton with Glucose and Methylene Blue dye medium and inoculated with 24-hr old standard Candida culture. Plates were divided into control and combination. Test discs with different concentrations of MgO were equidistantly placed in MgO Control, while sterile discs embedded with respective tissue conditioner were equidistantly placed in Viscogel and GC Soft controls. For combination groups, the tissue conditioners were mixed and the discs with MgO (1%, 3%, 5%, and 7%) were embedded in the mix. After 24 h of incubation, inhibition diameters were noted. Statistical Analysis Used : The data was analysed using Mann Whitney U Test, ANOVA, Tukey HSD test. Results : The inhibition effect of magnesium oxide 1% combined with tissue conditioners (VGC and GCC) is not significant in both the groups. The inhibition effect of MgO 5% and 7% combined with tissue conditioners (VGC and GCC) is very highly significant ( P < 0.001). Conclusions : Magnesium oxide in combination with tissue conditioners are effective against Candida albicans; GC soft with magnesium oxide showed a better result than Viscogel with magnesium oxide; Increasing the concentration of magnesium oxide increases the zone of inhibition of Candida albicans.