New insight into the microbiome, resistome, and mobilome on the dental waste water in the context of heavy metal environment.

Object: Hospital sewage have been associated with incorporation of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) into microbes, which is considered as a key indicator for the spread of antimicrobial resistance (AMR). The compositions of dental waste water (DWW) contain heavy metals, the evolution of AMR and its effects on the water environment in the context of heavy metal environment have not been seriously investigated. Thus, our major aims were to elucidate the evolution of AMR in DWW. Methods: DWW samples were collected from a major dental department. The presence of microbial communities, ARGs, and MGEs in untreated and treated (by filter membrane and ozone) samples were analyzed using metagenomics and bioinformatic methods. Results: DWW-associated resistomes included 1,208 types of ARGs, belonging to 29 antibiotic types/subtypes. The most abundant types/subtypes were ARGs of multidrug resistance and of antibiotics that were frequently used in the clinical practice. Pseudomonas putida, Pseudomonas aeruginosa, Chryseobacterium indologenes, Sphingomonas laterariae were the main bacteria which hosted these ARGs. Mobilomes in DWW consisted of 93 MGE subtypes which belonged to 8 MGE types. Transposases were the most frequently detected MGEs which formed networks of communications. For example, ISCrsp1 and tnpA.5/4/11 were the main transposases located in the central hubs of a network. These significant associations between ARGs and MGEs revealed the strong potential of ARGs transmission towards development of antimicrobial-resistant (AMR) bacteria. On the other hand, treatment of DWW using membranes and ozone was only effective in removing minor species of bacteria and types of ARGs and MGEs. Conclusion: DWW contained abundant ARGs, and MGEs, which contributed to the occurrence and spread of AMR bacteria. Consequently, DWW would seriously increase environmental health concerns which may be different but have been well-documented from hospital waste waters.

Cr2S3-Co3O4 on polyethylene glycol-chitosan nanocomposites with enhanced ultraviolet light photocatalysis activity, antibacterial and antioxidant studies.

A novel chromium sulfide-cobalt oxide nanostructures and decorated on Polyethylene Glycol (PEG)-chitosan (CS) nanocomposites as catalyst was synthesized by a facile method, and characterized by XRD, SEM, UV-Vis and XPS spectrum. The as-prepared Cr2S3-Co3O4/PEGCS composites represented the photo-decompose efficiency against the decomposition of basic dye (Rhodamine B (RhB)). The band gap of nano-catalyst was determined to be in the range of 2.61 to 3.32 eV. The introduction of Cr2S3 into Co3O4 increased the photocatalytic performance slightly, and decoration of Cr2S3-Co3O4 on PEGCS, which indicated the highest photo-degradation performance. Under the light irradiation, the active species OH and O2- radicals were important active agents in the photocatalysis process. The Cr2S3-Co3O4/PEGCS nanocomposites can maintain a stable photocatalysis performance after five cycles. Finally, the reaction mechanism of photo-degradation of RhB was put forward. The antibacterial test demonstrated the remarkable properties of Cr2S3-Co3O4/PEGCS nanocomposites in this research.

Study on a novel antibacterial light-cured resin composite containing nano-MgO.

A new type of photocurable resin composite containing nano-MgO was synthesized in order to reduce the occurrence of secondary caries. Different mass ratios (0 %, 1 %, 2 %, 4 %, 8 %) of nano-MgO were added into resin composites. The antibacterial properties of nano-MgO powder and modified resin composites against Streptococcus mutans (S. mutans) were detected by antibacterial ring test and film contact test, respectively. Compressive strength (CS) and wear resistance were determined by a universal testing machine and an abrasion test machine. The results indicated that antibacterial activity and wear resistance of resin composites containing nano-MgO were superior to the control group (p < 0.05). The antibacterial rate reached as high as 99.4 % when the mass ratio of nano-MgO was 8 %. However, the CS values tended to decline as the content of nano-MgO increase. Hence, the addition of nano-MgO showed excellent antibacterial property to resin composites and enhanced wear resistance, but was detrimental to their mechanical properties.

Structural characterization and directed modification of Sus scrofa SAMHD1 reveal the mechanism underlying deoxynucleotide regulation.

Sterile α-motif/histidine-aspartate domain-containing protein 1 (SAMHD1) is an intrinsic antiviral restriction factor known to play a vital role in preventing multiple viral infections and in the control of the cellular deoxynucleoside triphosphate (dNTP) pool. Human and mouse SAMHD1 have both been extensively studied; however, our knowledge on porcine SAMHD1 is limited. Here, we report our findings from comprehensive structural and functional studies on porcine SAMHD1. We determined the crystal structure of porcine SAMHD1 and showed that it forms a symmetric tetramer. Moreover, we modified the deoxynucleotide triphosphohydrolase (dNTPase) activity of SAMHD1 by site-directed mutagenesis based on the crystal structure, and obtained an artificial dimeric enzyme possessing high dNTPase activity. Taken together, our results define the mechanism underlying dNTP regulation and provide a deeper understanding of the regulation of porcine SAMHD1 functions. Directed modification of key residues based on the protein structure enhances the activity of the enzyme, which will be beneficial in the search for new antiviral strategies and for future translational applications.

Xylanase Treatment Suppresses Light- and Heat-Induced Yellowing of Pulp.

Xylanase is commonly applied in pulp and paper industries to ease cost-related and environmental pressures. The effect of xylanase treatment on pulp bleaching is well-established, however, few studies were conducted on the effects of xylanase treatment in pulp yellowing, especially the mechanism of pulp yellowing inhibition by xylanase treatment. In this study, pure xylanase (EC 3.2.1.8) was applied to treat wheat straw chemical pulp (CP) and poplar chemi-thermo-mechanical pulp (CTMP) to determine their effects on pulp brightness and on light- and heat-induced yellowing. The xylanase treatment decreased the post-color number of the pulps during light- and heat-induced yellowing. However, differences were observed in the yellowing inhibition between the wheat straw CP and poplar CTMP. The changes in chemical components of pulps after the xylanase treatment, for example, lignin, hemicellulose, and HexA contents, and analysis of UV-vis absorption spectra and Fourier transform infrared-attenuated total reflectance spectrum were used to explore the pulp yellowing inhibition causes by the xylanase treatment.

Fractionation of oil palm empty fruit bunch by bisulfite pretreatment for the production of bioethanol and high value products.

In this work, fractionation of empty fruit bunch (EFB) by bisulfite pretreatment was studied for the production of bioethanol and high value products to achieve biorefinery of EFB. EFB was fractionated to solid and liquor components by bisulfite process. The solid components were used for bioethanol production by quasi-simultaneous saccharification and fermentation. The liquor components were then converted to furfural by hydrolysis with sulfuric acid. Preliminary results showed that the concentration of furfural was highest at 18.8g/L with 0.75% sulfuric acid and reaction time of 25min. The conversion of xylose to furfural was 82.5%. Furthermore, we attempted to fractionate the liquor into hemicellulose sugars and lignin by different methods for producing potential chemicals, such as xylose, xylooligosaccharide, and lignosulfonate. Our research showed that the combination of bisulfite pretreatment and resin separation could effectively fractionate EFB components to produce bioethanol and other high value chemicals.

Silicon Oxycarbide/Carbon Nanohybrids with Tiny Silicon Oxycarbide Particles Embedded in Free Carbon Matrix Based on Photoactive Dental Methacrylates.

A new facile scalable method has been developed to synthesize silicon oxycarbide (SiOC)/carbon nanohybrids using difunctional dental methacrylate monomers as solvent and carbon source and the silane coupling agent as the precursor for SiOC. The content (from 100% to 40% by mass) and structure (ratio of disordered carbon over ordered carbon) of the free carbon matrix have been systematically tuned by varying the mass ratio of methacryloxypropyltrimethoxysilane (MPTMS) over the total mass of the resin monomers from 0.0 to 6.0. Compared to the bare carbon anode, the introduction of MPTMS significantly improves the electrochemical performance as a lithium-ion battery anode. The initial and cycled discharge/charge capacities of the SiOC/C nanohybrid anodes reach maximum with the MPTMS ratio of 0.50, which displays very good rate performance as well. Detailed structures and electrochemical performance as lithium-ion battery anodes have been systematically investigated. The structure-property correlation and corresponding mechanism have been discussed.

Facile Scalable Synthesis of TiO2/Carbon Nanohybrids with Ultrasmall TiO2 Nanoparticles Homogeneously Embedded in Carbon Matrix.

A facile scalable synthesis of TiO2/C nanohybrids inspired by polymeric dental restorative materials has been developed, which creates ultrasmall TiO2 nanoparticles homogeneously embedded in the carbon matrix. The average size of the nanoparticles is tuned between about 1 and 5 nm with the carbon content systematically increased from 0% to 65%. Imaging analysis and a scattering technique have been applied to investigate the morphology of the TiO2 nanoparticles. The composition, nature of carbon matrix, crystallinity, and tap density of the TiO2/C nanohybrids have been studied. The application of the TiO2/C nanohybrids as lithium-ion battery anode is demonstrated. Unusual discharge/charge profiles have been exhibited, where characteristic discharge/charge plateaus of crystalline TiO2 are significantly diminished. The tap density, cyclic capacities, and rate performance at high current densities (10 C, 20 C) of the TiO2/C nanohybrid anodes have been effectively improved compared to the bare carbon anode and the TiO2/C nanohybrids with larger particle size.