Yongzhang Zhu

Fracture behavior of AZ91 magnesium alloy

Abstract Optical microscopy and scanning electron microscopy (SEM) were used to examine the fracture behavior of AZ91 magnesium alloy ruptured by tensile and impact tests. AZ91 alloy generally revealed features of brittle fracture and cleavage is the principal fracture mode. The fracture behavior for tensile test is different from that for impact test due to different load forms. The fracture morphologies are different in different areas of the impact specimen. The Mg/Mg 17 Al 12 interface often acted as the crack initiation source.

Superplasticity and grain boundary sliding in rolled AZ91 magnesium alloy at high strain rates

Abstract The superplastic deformation characteristics and microstructure evolution of the rolled AZ91 magnesium alloys at temperatures ranging from 623 to 698 K (0.67–0.76 Tm) and at the high strain rates ranging from 10−3 to 1 s−1 were investigated with the methods of OM, SEM and TEM. An excellent superplasticity with the maximum elongation to failure of 455% was obtained at 623 K and the strain rate of 10−3 s−1 in the rolled AZ91 magnesium alloys and its strain rate sensitivity m is high, up to 0.64. The dominant deformation mechanism in high strain rate superplasticity is still grain boundary sliding (GBS), which was studied systematically in this study. The dislocation creep controlled by grain boundary diffusion was considered the main accommodation mechanism, which was observed in this study.

Complete Genome Sequence of Lactobacillus plantarum JDM1

Lactobacillus plantarum is a lactic acid bacterium (LAB) species commonly used as a probiotic. We have sequenced the genome of Lactobacillus plantarum JDM1, which is a Chinese commercial LAB with several probiotic functions, using a GS 20 system. We recommend that each commercial probiotic strain should undergo complete genome sequencing to ensure safety and stability.

In silico and microarray-based genomic approaches to identifying potential vaccine candidates against Leptospira interrogans

BackgroundCurrently available vaccines against leptospirosis are of low efficacy, have an unacceptable side-effect profile, do not induce long-term protection, and provide no cross-protection against the different serovars of pathogenic leptospira. The current major focus in leptospirosis research is to discover conserved protective antigens that may elicit longer-term protection against a broad range of Leptospira. There is a need to screen vaccine candidate genes in the genome of Leptospira interrogans.ResultsBioinformatics, comparative genomic hybridization (CGH) analysis and transcriptional analysis were used to identify vaccine candidates in the genome of L. interrogans serovar Lai strain #56601. Of a total of 4727 open reading frames (ORFs), 616 genes were predicted to encode surface-exposed proteins by P-CLASSIFIER combined with signal peptide prediction, α-helix transmembrane topology prediction, integral β-barrel outer membrane protein and lipoprotein prediction, as well as by retaining the genes shared by the two sequenced L. interrogans genomes and by subtracting genes with human homologues. A DNA microarray of L. interrogans strain #56601 was constructed for CGH analysis and transcriptome analysis in vitro. Three hundred and seven differential genes were identified in ten pathogenic serovars by CGH; 1427 genes had high transcriptional levels (Cy3 signal ≥ 342 and Cy5 signal ≥ 363.5, respectively). There were 565 genes in the intersection between the set encoding surface-exposed proteins and the set of 307 differential genes. The number of genes in the intersection between this set of 565 and the set of 1427 highly transcriptionally active genes was 226. These 226 genes were thus identified as putative vaccine candidates. The proteins encoded by these genes are not only potentially surface-exposed in the bacterium, but also conserved in two sequenced L. interrogans. Moreover, these genes are conserved among ten epidemic serovars in China and have high transcriptional levels in vitro.ConclusionOf the 4727 ORFs in the genome of L. interrogans, 226 genes were identified as vaccine candidates by bioinformatics, CGH and transcriptional analysis on the basis of the theory of reverse vaccinology. The proteins encoded by these genes might be useful as vaccine candidates as well as for diagnosis of leptospirosis.

Comparative proteogenomic analysis of the Leptospira interrogans virulence-attenuated strain IPAV against the pathogenic strain 56601

The virulence-attenuated Leptospira interrogans serovar Lai strain IPAV was derived by prolonged laboratory passage from a highly virulent ancestral strain isolated in China. We studied the genetic variations of IPAV that render it avirulent via comparative analysis against the pathogenic L. interrogans serovar Lai strain 56601. The complete genome sequence of the IPAV strain was determined and used to compare with, and then rectify and reannotate the genome sequence of strain 56601. Aside from their highly similar genomic structure and gene order, a total of 33 insertions, 53 deletions and 301 single-nucleotide variations (SNVs) were detected throughout the genome of IPAV directly affecting 101 genes, either in their 5′ upstream region or within their coding region. Among them, the majority of the 44 functional genes are involved in signal transduction, stress response, transmembrane transport and nitrogen metabolism. Comparative proteomic analysis based on quantitative liquid chromatography (LC)-MS/MS data revealed that among 1 627 selected pairs of orthologs, 174 genes in the IPAV strain were upregulated, with enrichment mainly in classes of energy production and lipid metabolism. In contrast, 228 genes in strain 56601 were upregulated, with the majority enriched in the categories of protein translation and DNA replication/repair. The combination of genomic and proteomic approaches illustrated that altered expression or mutations in critical genes, such as those encoding a Ser/Thr kinase, carbon-starvation protein CstA, glutamine synthetase, GTP-binding protein BipA, ribonucleotide-diphosphate reductase and phosphate transporter, and alterations in the translational profile of lipoproteins or outer membrane proteins are likely to account for the virulence attenuation in strain IPAV.

Behavior of Mg–6Al–xSi alloys during solution heat treatment at 420°C

Abstract The effect of solution heat treatment at 420°C on the morphology of Mg 2 Si particles in Mg–Al–Si alloys was investigated. The Mg 2 Si particles tended to be spherodized during the treatment due to the diffusion of Si atoms along the Mg 2 Si/Mg interface, which is benefit the mechanical properties of the alloys.

Whole genome sequencing revealed host adaptation-focused genomic plasticity of pathogenic Leptospira

Leptospirosis, caused by pathogenic Leptospira spp., has recently been recognized as an emerging infectious disease worldwide. Despite its severity and global importance, knowledge about the molecular pathogenesis and virulence evolution of Leptospira spp. remains limited. Here we sequenced and analyzed 102 isolates representing global sources. A high genomic variability were observed among different Leptospira species, which was attributed to massive gene gain and loss events allowing for adaptation to specific niche conditions and changing host environments. Horizontal gene transfer and gene duplication allowed the stepwise acquisition of virulence factors in pathogenic Leptospira evolved from a recent common ancestor. More importantly, the abundant expansion of specific virulence-related protein families, such as metalloproteases-associated paralogs, were exclusively identified in pathogenic species, reflecting the importance of these protein families in the pathogenesis of leptospirosis. Our observations also indicated that positive selection played a crucial role on this bacteria adaptation to hosts. These novel findings may lead to greater understanding of the global diversity and virulence evolution of Leptospira spp.

Complete Genome Sequence of Bifidobacterium longum JDM301

Bifidobacteria, known as probiotic bacteria, are high-G+C Gram-positive bacteria which naturally inhabit the human gastrointestinal tract and vagina. Recently, we completely sequenced Bifidobacterium longum JDM301, which is a widely used Chinese commercial strain with several probiotic properties.

Prevotella and Klebsiella proportions in fecal microbial communities are potential characteristic parameters for patients with major depressive disorder

BACKGROUND The diagnosis of major depression disorder (MDD) and other mental disorders were depended on some subjective survey scales. There are confirmed relationship between the gut flora and the mental states of MDD patients. METHODS The V3-V4 region of the 16S rRNA gene was extracted from the fecal microbial communities in MDD patients, PCR amplified and sequenced on the Illumina Miseq platform. RESULTS More phylum Firmicutes, less Bacteroidetes, and more genus Prevotella, Klebsiella, Streptococcus and Clostridium XI were found in MDD patients. The changes of the proportion of Prevotella and Klebsiella were consistent with Hamilton depression rating scale. LIMITATIONS The conclusion was limited by small sample sizes and potential uncontrollable influence factors on fecal microbiota. DISCUSSION Prevotella and Klebsiella proportion in fecal microbial communities should be concerned in the diagnosis and therapeutic monitoring of MDD in future.

Safety assessment of Lactobacillus plantarum JDM1 based on the complete genome

We performed a comprehensive safety assessment of a probiotic based on the whole genome sequence and corresponding phenotypes. This was performed on Lactobacillus plantarum JDM1, a widely used commercial probiotic strain in China. The minimal inhibitory concentrations (MICs) of sixteen antibiotics and the biogenic amine production of JDM1 were tested to supplement a traditional oral toxicity test. In total, fifty-one antibiotic resistance-associated genes, one hundred twenty-six virulence-associated genes, and twenty-three adverse metabolism-associated genes were found in JDM1. However, there were no toxin or hemolysin encoding genes, and safety-associated genes were rarely transferable. This approach can be generalized to provide a deep safety investigation of novel probiotic strains and greatly reveal the potential danger determinants and their molecular mechanisms. However, this kind of analysis reveals the theoretical maximum risk level as not all genes are efficient depending on environmental conditions.