Syntheses, characterization, and in vitro degradation of ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) copolymers by sequential ring-opening polymerization

Well-defined ethyl cellulose-graft-poly(epsilon-caprolactone) (EC-g-PCL) graft copolymers were successfully synthesized via ring-opening polymerization (ROP) of epsilon-caprolactone (CL) with an ethyl cellulose (EC) initiator and a tin 2-ethylhexanoate (Sn(Oct)2) catalyst in xylene at 120 degrees C. Then, novel ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) (EC-g-PCL-b-PLLA) graft-block copolymers were prepared by ROP of L-lactide (L-LA) with a hydroxyl-terminated EC-g-PCL macroinitiator and Sn(Oct)2 catalyst in bulk at 120 degrees C. Various graft and block lengths of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were obtained by adjusting the molar ratios of CL monomer to EC and the L-LA monomer to CL. The thermal properties and crystalline morphologies of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were different from those of linear PCL. The in vitro degradation rate of EC-g-PCL-b-PLLA was faster than those of linear PCL and EC-g-PCL due to the presence of PLLA blocks.     

转基因的分子生物学特性

现代分子生物学研究中,转基因概念的出现越来越频繁,它渐渐被用来表示所有的用基因工程手段构建、导入高等真核生物细胞,并稳定地整合入受体基因组的外源DNA．文章较系统地总结了已见报道的转基因的结构类型、它在受体细胞内的遗传学行为、表达特性和影响因素及其相应的生物学效应;分析了转基因研究中尚待研究的问题,提出了系统地进行转基因本身的分子生物学特性研究的必要性.     

Epigallocatechin gallate inhibits Streptococcus pneumoniae virulence by simultaneously targeting pneumolysin and sortase A

Streptococcus pneumoniae (pneumococcus), the causative agent of several human diseases, possesses numerous virulence factors associated with pneumococcal infection and pathogenesis. Pneumolysin (PLY), an important virulence factor, is a member of the cholesterol‐dependent cytolysin family and has cytolytic activity. Sortase A (SrtA), another crucial pneumococcal virulence determinate, contributes greatly to the anchoring of many virulence‐associated surface proteins to the cell wall. In this study, epigallocatechin gallate (EGCG), a natural compound with little known antipneumococcal activity, was shown to directly inhibit PLY‐mediated haemolysis and cytolysis by blocking the oligomerization of PLY and simultaneously reduce the peptidase activity of SrtA. The biofilm formation, production of neuraminidase A (NanA, the pneumococcal surface protein anchored by SrtA), and bacterial adhesion to human epithelial cells (Hep2) were inhibited effectively when S. pneumoniae D39 was cocultured with EGCG. The results from molecular dynamics simulations and mutational analysis confirmed the interaction of EGCG with PLY and SrtA, and EGCG binds to Glu277, Tyr358, and Arg359 in PLY and Thr169, Lys171, and Phe239 in SrtA. In vivo studies further demonstrated that EGCG protected mice against S. pneumoniae pneumonia. Our results imply that EGCG is an effective inhibitor of both PLY and SrtA and that an antivirulence strategy that directly targets PLY and SrtA using EGCG is a promising therapeutic option for S. pneumoniae pneumonia.     

以聚羟基丁酸戊酸共聚酯为碳源去除循环水养殖系统的硝酸盐及生物膜中微生物群落动态

【目的】利用聚羟基丁酸戊酸共聚酯(PHBV)作为固体碳源和生物膜载体,去除循环水养殖系统的硝酸盐,并研究固体碳源反硝化反应器不同运行阶段生物膜中微生物群落结构的动态变化。【方法】采用PCR-DGGE技术对反硝化反应器中微生物群落结构的动态变化进行了分析,采用传统纯培养方法分离反应器中降解PHBV的细菌。【结果】连接固相反硝化反应器能使循环水养殖系统中积累的硝酸盐显著降低,并维持在较低水平(小于10 mg/L),而常规循环水养殖系统中硝酸盐浓度持续增加。系统发育树聚类分析结果表明,反硝化反应器生物膜细菌归属于变形菌门(β-proteobacteria、γ-proteobacteria和δ-proteobacteria)、厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)。反应器运行初期(40 d)的优势种群主要为Acidovorax和Bacillus;运行后期(150 d)的优势种群依次为Clostridium、Desulfitobacterium、Dechloromonas、Pseudoxanthomonas和Flavobacterium。从反应器中分离到的PHBV降解菌株分别归属于Acidovorax、Methylibium、Pseudoxanthomonas和Dechloromonas。【结论】利用PHBV为碳源能有效去除循环水养殖系统的硝酸盐。明确了反硝化反应器在运行过程中,碳源表面生物膜的优势菌群及其动态变化。     

Inhibition of the type III secretion system by syringaldehyde protects mice from Salmonella enterica serovar Typhimurium

The invasiveness of Salmonella enterica serovar Typhimurium (S. Typhimurium) is closely associated with the Salmonella pathogenicity island (SPI)‐encoded type Ⅲ secretion system (T3SS), which can directly inject a series of effector proteins into eukaryotic cells to enable bacterial infection. In this study, syringaldehyde was identified as an effective inhibitor of the S. Typhimurium T3SS using an effector protein‐lactamase fusion reporter system. Syringaldehyde treatment could inhibit the expression of important effector proteins (SipA, SipB and SipC) at a concentration of 0.18 mM without affecting bacterial growth. Additionally, significant inhibition of bacterial invasion and cellular injury was observed following the syringaldehyde treatment in the co‐infection system of HeLa cells and S. Typhimurium. Furthermore, treatment with syringaldehyde provided systemic protection to mice infected with S. Typhimurium, reducing mortality (40.00%) and bacterial loads and relieving caecal damage and systemic inflammation. The results presented in this study indicate that syringaldehyde significantly affects T3SS activity and is a potential leading compound for treating S. Typhimurium infections.     

Anodes and Sodium‐Free Cathodes in Sodium Ion Batteries

The increase in electricity generation poses growing demands on energy storage systems, thus offering a chance for the success of the reliable and cost‐effective energy storage technologies. Sodium ion batteries are emerging as such a technology, which is however not yet mature enough to enter the market. At the crux of building practical sodium ion batteries is the development of electrode materials that promise sufficient cost‐ and performance‐competitiveness. As such, herein, all typical sodium storage materials are discussed, considering their fabrication methods and sodiation mechanisms in detail. A comprehensive cross‐literature and cross‐material comparison, which also includes the related thermodynamic analysis of their sodiation products, is also provided. The review focusses particularly on anodes and sodium‐free cathodes, as they both play the role of the acceptor rather than the donor of sodium ions in their operation in batteries; their difference lies in the (de‐)sodiation voltage. In the discussion, special attention is paid to contradictory observations and interpretations in contemporary sodium ion battery research, since debates on these controversies are likely to fuel future sodium battery research.     

Evaluation of High-Resolution Melting for Gene Mapping in Rice

In this study, high-resolution melting (HRM) analysis was evaluated for gene mapping in rice with sequence-tagged site (STS) and simple sequence repeat (SSR) markers. A total of 103 out of 353 normal STS and SSR markers revealed polymorphic melting curves among the parental genotypes, and 12 of these were successfully used to genotype the F₂ mapping population for HRM analysis. Additional electrophoresis findings demonstrated that HRM genotyping matched with traditional electrophoresis results. To optimize the HRM-marker screening efficiency, different HRM reaction conditions were evaluated. A 5-μl touchdown-polymerase chain reaction (PCR) system provided no significant improvement in screening efficiency but in a 10-μl touchdown-PCR system, the marker screening efficiency increased by 75%. Twenty-one markers were obtained for mapping purposes under the optimized reaction conditions. This study indicates that HRM analysis can speed up the gene mapping progress in rice, while saving a lot of manpower.     

Considerable MHC diversity suggests that the functional extinction of baiji is not related to population genetic collapse

To further extend our understanding of the mechanism causing the current nearly extinct status of the baiji (Lipotes vexillifer), one of the most critically endangered species in the world, genetic diversity at the major histocompatibility complex (MHC) class II DRB locus was investigated in the baiji. Nine highly divergent DRB alleles were identified in 17 samples, with an average of 28.4 (13.2%) nucleotide difference and 16.7 (23.5%) amino acid difference between alleles. The unexpectedly high levels of DRB allelic diversity in the baiji may partly be attributable to its evolutionary adaptations to the freshwater environment which is regarded to have a higher parasite diversity compared to the marine environment. In addition, balancing selection was found to be the main mechanisms in generating sequence diversity at baiji DRB gene. Considerable sequence variation at the adaptive MHC genes despite of significant loss of neutral genetic variation in baiji genome might suggest that intense selection has overpowered random genetic drift as the main evolutionary forces, which further suggested that the critically endangered or nearly extinct status of the baiji is not an outcome of genetic collapse.     

Quercetin protects rats from catheter‐related Staphylococcus aureus infections by inhibiting coagulase activity

Coagulase (Coa) activity is essential for the virulence of Staphylococcus aureus (S aureus), one of the most important pathogenic bacteria leading to catheter‐related bloodstream infections (CRBSI). We have demonstrated that the mutation of coagulase improved outcomes in disease models of S aureus CRBSI, suggesting that targeting Coa may represent a novel antiinfective strategy for CRBSI. Here, we found that quercetin, a natural compound that does not affect S aureus viability, could inhibit Coa activity. Chemical biological analysis revealed that the direct engagement of quercetin with the active site (residues Tyr187, Leu221 and His228) of Coa inhibited its activity. Furthermore, treatment with quercetin reduced the retention of bacteria on catheter surfaces, decreased the bacterial load in the kidneys and alleviated kidney abscesses in vivo. These data suggest that antiinfective therapy targeting Coa with quercetin may represent a novel strategy and provide a new leading compound with which to combat bacterial infections.