Abstract:7,8-dihydro-8-oxoguanine (7,8-dihydro-8-oxoguanine, 8oxoG) is a common DNA damage base. Because 8oxoG can form a pair with adenine, the replication of 8oxoG before being repaired would lead to the mutation of GC → TA, thereby causing genome instability. Base excision repair (BER) is a typical pathway to repair 8oxoG in DNA, among which 8oxoG DNA glycosylases (OGGs) are the key enzymes that initiate a BER pathway. Previous studies showed that OGG can recognize and excise 8oxoG in DNA, thereby preventing the accumulation of GC → TA mutations in cells. Currently, OGG, which is widely distributed in bacteria, archaea and eukaryotes, has been divided into three families:OGG1, OGG2 and AGOG (archaeal 8oxoG DNA glycosylase). Archaeal genomic sequences suggest that they encode at least one OGG. Currently, a few OGGs of bacteria and eukaryotes have been extensively studied, but there have been several studies on OGGs of hyperthermophilic archaea, which is still in the early stage. Research progress of OGGs of hyperthermophilic archaea was reviewed and the prospects for future research were proposed in this article.

Abstract:Streptococcal toxic shock syndrome (STSS) is a rapidly progressing, life-threatening, systemic reaction to invasive infection caused by streptococci, which is characterized by a cytokine storm in the host. Although the majority of clinical STSS cases are triggered by the superantigens (SAgs), a few STSS cases are not associated with SAgs and the related mechanisms are considered to be complicated. Here, we review the recent research progress on the mechanism of SAgs-independent STSS, including the activation of inflammatory signaling pathways in host triggered by Streptococcus,the activation of inflammatosomes and pyroptosis, the pro-inflammatory cytokines and cytokine storm. We also summarize cell and animal models usually used in STSS research. This review is useful for a better understanding of STSS and provides a theoretical foundation for the research of STSS mechanism.

Abstract:In recent years, glycosylation modification system in bacteria has attracted more and more attention in both academic and industrial fields. Numerous glycosylation modification systems in bacteria have been reported, the most representative cases are N-glycosylation modification system in Campylobacter jejuni and O-glycosylation modification system in Neisseria meningitidis. This review systematically summarizes the glycosylation modification system in bacteria to better understand this system and enlists the situation of the application using the protein glycosylation modification system in bacteria. At the same time, we provide some theoretical knowledges and examples for the design of virus-like particle-based vaccines where glycosylation is required.

Abstract:Fluorine is a kind of halogen with special properties. Fluorine-containing organic substances can be widely used in bioorganic chemistry, medicinal chemistry, biomaterial science and other fields. Despite innovation of synthetic C-F bond forming methods, selective fluorination is still very challenging. Therefore, it is necessary to use fluorine biochemical methods to selectively introduce fluorine into molecules with diverse structures, but few methods can incorporate fluorine into bioactive molecules with complex structures. Therefore, we review here the discovery of fluorinated natural products and fluorinases in nature, the synthetic pathway of fluorinated natural products, the significance of fluorinated natural product synthesis mechanism, the evolution of fluorinases and the synthesis of fluoride, and the application of fluorinases and fluoride. This review will provide information for fluoride biosynthesis and promote the industrialization process of fluoride biosynthesis.

Abstract:Syphilis, an infectious disease caused by Treponema pallidum subspecies pallidum, is mainly transmitted through mother-to-child infection or sexual contact. The outer membrane proteins of T. pallidum play important roles in the transmission and the adhesion to the hosts. Therefore, the identification of outer membrane proteins from T. pallidum, which can be used as the target of antibiotics, has become the research focus of vaccine development for syphilis. This review focuses on the structural and functional research of the outer membrane proteins of T. pallidum, and also summarizes the current research progresses on the development of drugs that target bacterial outer membrane proteins, in order to provide an overview and perspective aiming at the development of new drugs against T. pallidum.

Abstract:Kangillaceae is a family under the order Oceanosprillales that contains the genera Kangiella, Aliikangiella and Pleionea. The presence of abundant genes encoding extracellular proteases in the highly streamlined genome of the genus Kangiella suggests that it contributes significantly to the degradation of protein components in marine particulate organic matter. Considering that the type strains of Kangilla exclusively utilize protein as nutrient sources, we suggest to translate the genus as "Shi Ruan Jun" (protein degrading bacteria) in Chinese. In this paper, we review the research progress to identify novel species and phylogeny of Kangielleace. Based on the reconstituted metabolic networks of Kangiella, we reveal the potential ecological functions of this group of marine bacteria.

Abstract:The introduction of chemical nitrogen fertilizer has greatly increased the crop yield. However, the excessive fertilization or improper fertilizer use will cause severe damage to the agro-ecology system. Understanding characteristics of plants and seeking alternative nitrogen (N) sources are crucial to reduce the use of fertilizer and increase nutrient efficiency. The biological nitrogen fixation established between plants and microorganisms can provide a large amount of clean N sources for the host, which plays an irreplaceable role in agricultural production. Here, we take sugarcane as an example to summarize the progresses of the associative N₂ fixation, including the discovery, screening, infection mechanisms and functional study of plant-associated N₂-fixing bacteria, and the application of the mixed inoculations with diazotrophic bacteria in sugarcane production. We predict that these will provide theoretical basis and reference value for improvement of nutrient efficiency and promotion of biological nitrogen fixation in agricultural production.

Abstract:Campylobacter is an important zoonotic pathogen causing gastroenteritis worldwide, and poses a serious threat to public health. The complexity of prevalence, transmission, and diffusion is associated with high genomic variations of Campylobacter. Whole Genome Sequencing (WGS) is an efficient tool to identify species quickly and accurately, analyze the differences between different individual genomes, predict bacterial resistance, virulence genes and population evolution models on the genetic level. Here we review the application of the whole genome sequencing in Campylobacter genomic analysis to provide a basis for the prevalence and prevention of Campylobacter.

Abstract:The innate immune system is the first line of defense against viral infection. Upon virus infection, host cells trigger immune response and initiate the immune mechanism of inhibiting virus replication. Meanwhile, viruses have evolved various mechanisms to counteract the host innate immune signaling pathway, including evading from host pathogen recognition receptors recognition and hijack host proteins to facilitate their own proliferation. DEAD (Asp-Glu-Ala-Asp, DexD/H) helicase family is a class of functional proteins existing in host cells. They play a key role in various cellular processes, such as transcription, splicing, mRNA synthesis and translation. Members of this family have the ability to recognize RNA and participate in multiple cellular processes, so they can affect the innate immune responses caused by viral infection in many ways. This paper reviews the research on DEAD-box RNA helicase in innate immunity to provide reference for related studies.

Abstract:[Objective] Sporisorium scitamineum isa pathogenic fungus that causes sugarcane smut, the most important disease of sugarcane in China. Tracing the infection progression of the disease will help to reveal the mechanism of resistance to smut and lay a foundation for the selection of resistant cultivars and the control of smut. [Methods] We labeled the basidiospores of the pathogen with a gene that encodes the enhanced yellow fluorescent protein (eYFP) by Agrobacterium tumefaciens-mediated transformation (ATMT). We tested the mating and pathogenicity of the transformants. To visualize the early stage of infection, we injected the eYFP-tagged strains into smut susceptible sugarcane cultivar ROC22 and smut resistant cultivar Zhongzhe 1, Zhongzhe 6, Zhongzhe 9. [Results] The eYFP-tagged strains were indistinguishable to the wild-type strain in mating and pathogenicity, and the fluorescence was able to inherit into the teliospores. Laser confocal microscopic examination showed that at 5 days post inoculation, a few aggregated as well as separated mycelia were observed in the susceptible sugarcane cultivar ROC22, but only a small amount of single mycelium was found at the same time in the resistant Zhongzhe cultivars. Much more aggregated mycelia were found at 35 days post infection in ROC22 than in Zhongzhe cultivars, with the lowest number in Zhongzhe 1. [Conclusion] A fluorescent tracer system for sugarcane infection by S. scitamineum was successfully constructed, and there may be a mechanism to constrain the mycelial growth of S. scitamineum in Zhongzhe cultivars.

Abstract:[Objective] Multifarious modular modifications in type I polyketide synthase (PKS) serve as crucial contributing factors for the diversity of polyketides. Ansamitocins, an antitumor agent, possess unique olefin shifts in the region of C11-C14, which might be catalyzed by dehydratase domain in PKS module 2 and 3. We evaluated the biochemical function of dehydratase domain in module 2 (Ansa DH₂). [Methods] Using ansamitocin-producing strain Actinosynnema pretiosum subsp. pretiosum ATCC 31280, we chose four different Ansa DHs in the ansamitocin biosynthetic modules to achieve bioinformatics analysis. Coupled with chemical synthesis of an analogue substrate waq-1 of Ansa DH₂, we presented our in vitro investigations. ESI-MS² analysis revealed the structure of the final product, which confirmed the α-β dehydration activity of Ansa DH₂. Ultimately, the correlation between the catalytic function and requisite amino acid residues has been determined through site-directed mutagenesis. [Results] Bioinformatics analysis suggests that Ansa DH₂ and Ansa DH₃ were closely related to those known DHs, which are responsible for olefin shift. An effective synthetic route was accomplished to afford waq-1 in 17.81% yield over six linear steps. The conversion rate of waq-1 reached 45% after 36 h by optimized in vitro enzymatic reactions. The α-β dehydration activity of Ansa DH₂ was reaffirmed by fragmentations in MS² profiles. Residue His48 in Ansa DH₂ was turned out to be indispensable for dehydration function by site-directed mutagenesis. [Conclusion] This work focused on the biochemical function of Ansa DH₂, which not only verified its α-β dehydration activity, but also shed light on further mechanistic study of olefin shift.

Abstract:[Objective] To establish a receptor-binding capture method for recombinant adeno-associated virus (rAAV) purification. [Methods] We expressed polycystic kidney disease (PKD) domains 1 and 2 of AAV receptor in E. coli as an elastin-like polypeptide (ELP) fusion protein. We purified the fusion protein by inverse transition cycling (ITC). We generated two versions of rAAV-GFP and incubated them with ELP-PKD protein. We recovered the protein-bound rAAV-GFP by ITC and extracted the viral DNA for PCR analysis. We optimized the conditions for rAAV-GFP purification and identified the purified rAAV by electron microscopy and Western blotting. [Results] ELP-PKD fusion protein was correctly expressed as a soluble protein which was purified to more than 90% purity. We demonstrated the specific affinity of ELP-PKD fusion protein for rAAV-GFP binding. We purified rAAV-GFP with 58% recovery from insect cells or 56% recovery from AAV-293 cells. After elution, we obtained final rAAV-GFP recovery rates of 46% and 44% from the two cell types, respectively. We demonstrated that the purified rAAV-GFP had the typical morphology and structural proteins of AAV. [Conclusion] We established ELP-PKD-binding capture method for quick purification of rAAV from different cell types.

Abstract:[Objective] The gene MCHK_1326 from Mesorhizobium huakuii 7653R encoding an outer membrane porins may be involved in the process of rhizobial infection, nodulation and symbiotic nitrogen fixation. This study was aimed to explore the function of this gene in legume-rhizobium symbiosis. [Methods] Bioinformatics analysis used to study the structural characteristics and biological functions of MCHK_1326 protein. The spatial and temporal expression characteristics of MCHK_1326 gene was assayed by histochemical staining. The deletion mutant strain (7653R△1326 strain) was constructed by the Cre-loxp system. Early infection events and symbiotic phenotype of wild-type and mutant strain were observed. The symbiotic phenotype of the mutant strain was also measured under the conditions of adding nitrogen source. [Results] The gene MCHK_1326 was highly expressed during the entire early phase of infection and in the infection zone of mature nodules, such as the elongation process of the infected thread. The infection threads and the number of nodules primordium by the mutant were significantly reduced; compared with the controls, the plants inoculated with 7653RΔ1326 strain displayed significant reduction in the fresh weight of the aerial plant, nitrogenase activity, and the amount and weight of nodules of 7653Δ1326 strain was significantly lower. The defected symbiotic phenotype of plants inoculated with 7653RΔ1326 strain could be restored to normal by adding inorganic nitrogen source. [Conclusion] The gene MCHK_1326 participates in the early infection and nodulation processes and plays an important role in the development of nodule and symbiotic nitrogen fixation.

Abstract:[Objective] To provide biocontrol bacteria to control various plant fungal diseases, this study aimed to explore the antagonistic compounds from Bacillus methylotrophicus against Cercospora zeae-maydisTehon et Daniels, Alternaria alternate and Botrytis cinerea. [Methods] Plate method was used for prescreening, and the cup and saucer method was applied for rescreening. The antagonistic strains were identified by cell morphology and 16S rRNA gene. Antagonistic compounds were analyzed by thin-layer chromatography and their coding genes were amplified by the polymerase chain reaction. Corn field trial of biocontrol was used to assess the control effect of antagonistic strain on three pathogenic microorganisms. [Results] Bacillus methylotrophic B-1841 inhibited A. alternata, C. zeae-maydis and B. cinerea with 65.95%, 71.04% and 46.69%, respectively. The antagonistic compounds were identified as iturin-like lipopeptide. The corn field trial showed that strain B-1841 had significant control effects on diseases infected by C. zeae-maydis, A. alternate and B. cinerea, with relative control effects of 69.89%, 60.25% and 45.21%, respectively. [Conclusion] B. methylotrophic B-1841 has a potential application prospect in the prevention and treatment of fungal diseases of crops.

Abstract:[Objective] The intestinal tract comprises the main digestive organs of animals and is an important barrier that confers organism resistance to exogenous pathogens. The intestinal flora of animals is reportedly related to animal species, feeding methods and growth stage. However, it is unclear whether the intestinal bacteria of house-feeding Tibetan, grazing Tibetan and Landrace, York and Duroc (DLY) three-way hybrid pigs differ. [Methods] The intestinal tissues of 6-month-old to 7-month-old grazing Tibetan, house-feeding Tibetan and DLY pigs were selected. The intestinal morphology of each pig was determined by tissue section method. The digestive enzyme activity of intestinal contents was determined by using an enzyme activity assay kit. The intestinal microbiota was examined through high-throughput sequencing technology. [Results] The muscular thickness and villus height of duodenum, jejunum and ileum of DLY pigs were significantly higher than those of Tibetan pigs. The crypt depth of the duodenum, jejunum and ileum of DLY pigs was significantly lower than that of Tibetan pigs. The intestinal morphology was not significantly different between grazing and house-feeding Tibetan pigs. The trypsin activity in the small intestines of DLY pigs was remarkably higher than that of Tibetan pigs, whereas the amylase activity in the small intestines of DLY pigs was noticeably lower than that of Tibetan pigs. The dominant phyla in all three groups were Proteobacteria, Firmicutes and Bacteroidetes. The dominant genera in Tibetan pigs were Ralstonia and Escherichia, whereas the dominant genera in DLY pigs were Ralstonia and Bradyrhizobium, but the contents were significantly different. The similarity of the intestinal bacterial community structure between house-feeding and grazing Tibetan pigs was higher than that between Tibetan and DLY pigs. [Conclusion] Significant differences in intestinal morphology, digestive enzyme activity and intestinal microbial structure were observed among grazing Tibetan, house-feeding Tibetan and DLY pigs.

Abstract:[Objective] Ascosphaera apis is a fungal pathogen that exclusively infects honeybee larvae, leading to chalkbrood, which is a chronic disease in beekeeping industry and results in heavy losses for apiculture. The objective of this work is to investigate alternative splicing (AS) and alternative polyadenylation (APA) of genes in A. apis mycelium (Aam) and spore (Aas) based on previously gained third-generation long-read sequencing dataset. [Methods] The type of AS events occurred in genes in Aam and Aaswas identified. The visualization of partial isoforms' structures was performed with IGV browser. APA sites of genes in Aam and Aas were identified using TAPIS pipeline. MEME software was used to investigate characteristics of sequences at 50 bp upstream of APA sites followed by identification of motifs. [Results] In total, 286 AS events were identified in Aam, including 162 retained intron (RI), 87 alternative 3ʹ splice-site (A3), 32 alternative 5ʹ splice-site (A5) and five skipping exon (SE), while 559 AS events were identified in Aas, including 305 RI, 155 A3, 85 A5, 13 SE and one mutually exclusive exon (MEE). Further analysis suggested that majority of annotated genes in current reference genome are incomplete, number and structure of partial annotated genes in mycelium differ from those in spore, and for part of isoforms, there are no corresponding annotated genes in reference genome. Additionally, a total of 2748 genes in Aam were observed to contain one and more APA sites, among them those containing one APA site was the largest group (726, 26.42%); while in Aas 2768 gene were found to contain one and more APA sites, and those containing more than five APA sites were the most abundant (1180, 42.63%). Besides, part of genes in A. apis mycelium and spore were detected to have various APA sites. Moreover, analysis of sequence characteristics indicated that upstream and downstream sequences of 3ʹ UTR of A. apis full-length transcripts have an obvious base bias, and U and A were respectively enriched in the upstream and downstream. Moreover, four motifs were identified at the upstream of APA sites of A. apis full-length transcripts, including UCUCCU, UCUUCU, CCCACC and CCCCCU. [Conclusion] In this study, AS and APA of genes in A. apis mycelium and spore were deeply analyzed, the results uncovered the complexity of A. apis transcriptome, offering valuable information for improvement of current genome and transcriptome annotations and a pivotal foundation for exploration of the function of AS and APA involved in regulation of A. apis gene expression.

Abstract:[Objective] In order to clarify the bacterial community structure in the midgut and hindgut of adult Monochamus alternatus, and to explore the potential function of intestinal bacteria. [Methods] The gut DNA from 15 individuals (15 midguts, 15 hindguts of outdoor and 15 midguts, 15 hindguts of indoor) of adult Monochamus alternatus fed indoors and outdoors were extracted. The 16S rDNA V3-V4 region of the intestinal bacteria of Monochamus alternatus was sequenced through next generation sequencing techniques. The number of OTUs was counted, the species composition, alpha diversity and beta diversity were analyzed, and the functions of intestinal bacteria were predicted by PICRUSt software. [Results] A total of 544180 high-quality sequences were obtained and clustered into 615 OTUs under 97% similarity, which were annotated into 22 phyla, 48 classes, 112 orders, 172 families, 285 genera and 408 species. The number of OTUs in indoor population was more than that in outdoor population, and there were differences between indoor and outdoor population. The difference between midgut and hindgut of the same population was not obvious. Proteobacteria was the most dominant genus of intestinal bacteria in both indoor and outdoor populations of Monochamus alternatus; Enterobacter was the most dominant genus of intestinal bacteria in outdoor populations and hindgut bacteria in indoor populations, Serratia was the most dominant genus of midgut bacteria in indoor populations. The results of alpha diversity showed that the richness of intestinal bacterial community in indoor populations was significantly higher than that in outdoor populations, and the beta diversity showed that the homogeneity and stability of intestinal bacterial community in outdoor populations were better than that in indoor populations. There was no significant difference in bacterial richness and diversity between the midgut and hindgut of outdoor and indoor populations. The results of functional prediction showed that the metabolic pathway was the most abundant in the intestinal bacteria of adults, which mainly consisted of carbohydrate metabolism and amino acid metabolism, and these bacteria were also able to degrade xenobiotics, terpenoids, polyketides and other secondary metabolites. There was no significant difference in functional abundance among different populations and different intestinal segments. [Conclusion] The community structure and difference of bacteria in the midgut and hindgut of adult Monochamus alternatus fed on different food were determined. The potential role of intestinal bacteria was understood, which provided a theoretical basis for further investigating the function of intestinal symbiosis bacteria of Monochamus alternatus.

Abstract:[Objective] To analyze the effect of MpigE (one of Monascus purpureus genes) deletion on the transcription of Monascus pigments. [Methods] The wild-type Monascus purpureus Mp-21 and the △MpigE were analyzed by high-throughput transcriptome sequencing, annotation, enrichment of gene function analysis and gene expression differences pathway enrichment analysis. The transcription level revealed the reason for the change of pigment production after MpigE deletion. [Results] By RNA-seq sequencing, 7.5-8.5Gb of original data were obtained from each sample, and 7219 Unigenes were obtained after de novo assembly, among which 5692 were successfully annotated. The enrichment analysis of differentially expressed genes showed that compared with the wild-type strain of Mp-21, △MpigE had 199 up-regulated differentially expressed genes and 293 down-regulated differentially expressed genes. [Conclusion] The deletion of MpigE can affect the biosynthesis of pigment by promoting the expression of central carbon metabolism and acetyl-CoA metabolism-related genes in Monascus.

Abstract:[Objective] The purpose of this study was to study the physicochemical properties of the virus RHDV2 and evaluate effect of different treatment to kill the virus. [Methods] The virus was identified by RT-PCR in rabbits with clinical suspected death from RHDV2 infection. The physicochemical properties of RHDV2 were studied by PMA-RT-qPCR at different pH, different temperatures, common veterinary disinfectants and different concentrations of formaldehyde. [Results] RHDV2 infection was confirmed by RT-PCR detection and sequencing analysis. The VP60 gene sequence of this strain was 98.35% consistent with RHDV2 in GenBank (MN276176.1). PMA-RT-qPCR results show that RHDV2 was sensitive to pH, high temperature, animal disinfectant and formaldehyde. The killing rate of virus increased with pH decreasing or increasing. The virus killing rate reached 77.61% after being treated at 65℃ for 30 min, and 95.10% after being treated at 83℃ for 5 min. RHDV2 is sensitive to all three animal disinfectants, among which povidone iodine had the best killing effect on RHDV2, the virus killing rate reached 88.78% after 30 min. The killing rate of 0.3% formaldehyde was better than 0.2%, and after 30 min of application, the killing rate could reach 82.22%. [Conclusion] RHDV2 is sensitive to acid and base, high temperature, animal disinfectant and formaldehyde to varying degrees.

Abstract:[Objective] The important foodborne bacterial pathogen Listeria monocytogenes uses the glutaredoxin (Grx) system to defend the oxidative stress during environmental adaption. Here, we explore biological characteristics of the glutathione reductase (GR) during bacterial infection. [Methods] We constructed the gr deletion and complementation strains to compare the abilities in bacterial growth, motility, oxidative tolerance and cellular infection. Besides, the gr promoter-based fluorescent report system (FRS) was genetically obtained to further study regulation of gr by Grx. [Results] Our data show that deletion of gr did not affect bacterial growth but enhanced the capability of swarming. Additionally, lack of gr significantly increased oxidative tolerance of bacteria under Cu²⁺ and Cd²⁺ stress, as well as increased efficiencies of intracellular infection in Caco-2 and RAW264.7 cells. Importantly, transcription of gr was negatively regulated by Grx. [Conclusion] The glutathione reductase plays a critical role in bacterial flagella-based swarming motility and correlates a regulatory relationship with the Grx system. Also, GR plays a non-classical role in bacterial oxidative resistance and intracellular infection. This study will expand our understanding of the redox regulatory mechanisms exploited by intracellular bacteria during adaption outside the environment and inside the host, which provides novel strategies to prevent and control the foodborne diseases.

Abstract:[Objective] To analyze the microbiome composition and community characteristics of the foregut, midgut and hindgut of grass carp from different habitats. [Methods] The 16S rRNA high-throughput sequencing technology was applied to analyze the microbial composition and community characteristics of the foregut, midgut and hindgut of grass carp from four habitats, including river, lake, high-density pond culture and low-density reservoir culture. [Results] Venn diagram, Rarefaction Curve and Alpha index showed that microbial diversity of the foregut was higher in the cultured habitats than natural habitats (river and lake), whereas the diversity of the hindgut microbial community had the opposite trend. The microbial composition and community characteristics of the foregut of grass carp in different habitats varied greatly:the dominant microflora in the foregut was Acinetobacter and Cupriavidus in natural habitats, Cetobacterium and Shewanella in high-density culture pond, and Streptococcus and Peptostreptococcus in low-density culture reservoir. [Conclusion] The great differences in foregut microbial composition and community characteristics of grass carp were due to the difference of environmental factors, culture methods and diets. Our findings can provide basic data for the study of intestinal microorganisms of grass carp. There is a potential risk of infection for grass carp in high-density culture habitats, suggesting that the culture density should be controlled as much as possible in the culture of grass carp.

Abstract:[Objective] Silver nanoclusters were prepared using Pichia guilliermondii ZJC-1 for the detection of trace Cr(VI). [Methods] Fluorescent silver nanoclusters were synthesized using Pichia guilliermondii ZJC-1 that was acclimated to silver. The structures and fluorescence properties of silver nanoclusters were characterized. Then we explored the selective quenching effect of Cr(VI) on the silver nanoclusters fluorescence. We also established a linear relationship between silver nanoclusters fluorescence intensity and the concentration of Cr(VI). The effect of pH and other metal ions on the detection of Cr(VI) was also examined. [Results] There was a good linear relationship between Cr(VI) and the fluorescence intensity of silver nanoclusters (R²=0.9821). The detection limit was 184 μmol/L and the signal to noise ratio (SNR) was 3. Using this method to detect Cr(VI) in actual water samples (Songhua River, Majiagou River) the recovery rate was between 97.73% and 102.88%. [Conclusion] Silver nanoclusters with good fluorescence properties can detect trace concentrations of Cr(VI) simply and rapidly.

Abstract:[Objective] Our study aims to measure the changes of microbial flora in feces of healthy postpartum cows and cows suffering from left displacement of the abomasum (LDA), so as to explore the relevance between LDA occurrence and the flora, and assess its potential impact on body metabolism. [Methods] We used 16S rDNA High-Throughput Sequencing technology to determine the 16S rDNA V3-V4 region sequence of microorganisms in the feces of 10 healthy cows and 10 cows with LDA. [Results] The diversity analysis indicated that there were significant differences in microbial diversity and community composition between healthy group and LDA group, and the fecal microbes of the LDA cows had higher species abundance and population differences. The analysis of the top 10 species with the largest abundance at the level of phyla, family, and genus showed that the abundances of Verrucomicrobia, Cyanobacteria, Proteobacteria, Fusobacteria, Bacteroides, p-2534-18B5, Mogibacteriaceae, Fusobacteriaceae, Oscillospira, 5-7N15 and Faecococcus in LDA cows increasedsignificantly (P<0.05), while the abundances of Spirochetes, TM7, Ruminococcaceae, Rikenellaceae and Treponema decreased significantly (P<0.05). Functional prediction analysis showed that the functional genes related to carbohydrate metabolism and lipid metabolism pathway in cows with LDA were greatly up-regulated, while those related to genetic information processing were significantly down regulated. [Conclusion] Our findings confirm that the changes of fecal microorganisms in dairy cows before and after LDA, and provide a foundation for a deeper understanding of the pathogenesis and early diagnosis of LDA.

Abstract:[Objective] In this study, we investigated the relationship between the VgrS-VgrR two-component system (TCS) of Xanthomonas axonopodis pv. manihotis (Xam) and the bacterial pathogenicity. The study can provide molecular biological evidence for the effective prevention and control of cassava bacterial blight. [Methods] We constructed the insertion-inactivation mutants of vgrS and vgrR by homologous recombination, and constructed the complementary strains of each mutant by using the mobile cosmid vector pHM1. The study measured the pathogenicity of each mutant, its swimming and the changing in extracellular enzyme and extracellular polysaccharide production. We also observed the bacterial response to hydrogen peroxide and metal ion stress. [Results] Compared with wild-type strain, both vgrS and vgrR mutants exhibited significantly reduced pathogenicity after inoculation of the host plant cassava. Both mutants exhibited decreased swimming, reduced protease activity and hydrogen peroxide tolerance. Under the stress conditions of high concentrations of metal ions Fe²⁺, Fe³⁺, Cu²⁺, Ni²⁺, Zn²⁺ and Cu²⁺, the mutants' growth were also significantly decreased. However, the extracellular polysaccharide content of vgrS and vgrR mutants increased dramatically, which was 2.14 and 1.89 times that of the wild type, respectively. [Conclusion] The results clarified the important role of the VgrS-VgrR TCS in the pathogenesis of Xam, and provided clues for further research on the regulation mechanism of VgrS-VgrR and drug screening targeting Xam.