Abstract:Abstract:Carboxylatic acids have been widely used in food，pharmaceutical and chemical industries．As a eukaryotic model organism， Saccharomyces cerevisiae is thought as cell factory to produce organic acids through manipulating metabolic pathway．In this review，we addressed the metabolic engineering strategies to construct a high titer route converting pyruvate to target carboxylate，and to explore how to divert the carbon flux to desired product from ethanol．Furthermore，we also discussed the mechanisms for carboxylate transport and energy involved in． Finally，the relevant strategies for development in future are proposed．

Abstract:Abstract:The study on bacterial capsular polysaccharide is deeper with the development of the molecular biology，saccharide chemistry and immunology． Not only the character and structure of bacterial capsular polysaccharide was researched，but also the genes related to the synthesis，regulation and pathogenicity． This review focuses on the chemical structure，synthesis genes，mechanisms of the diversity，synthesis regulation，function，pathogenicity and application of the bacterial capsular polysaccharide． The research hot spots are also summarized to supply the basic theory and threads to study and apply bacterial capsular polysaccharide．

Abstract:Abstract:Microbial communities are the engines that drive the global biogeochemical cycle of carbon and nitrogen essential for life on Earth． However，microorganisms have evolved as a result of complex interactions with other organisms and environments． Deciphering the metabolism of microorganisms at the community level in nature will be crucial for a better understanding of the mechanisms that lead to the enormous divergence of microbial ecophysiology． Due to the immense number of uncultivated microbial species and the complexity of microbial communities，delineating community metabolism proves a virtually insurmountable hurdle．By tracing the heavy isotope flow of key elements such as carbon and nitrogen，DNA-based stable isotope probing (DNA-SIP) can provide unequivocal evidence for substrate assimilation by microorganisms in complex environments． The essential prerequisite for a successful DNA-SIP is the identification，with confidence，of isotopically enriched 13 C-DNA，of which the amount is generally too low to allow the direct measurement of 13 C atom percent of nucleic acid． The methodological considerations for obtaining unambiguous DNA highly enriched in heavy isotope are presented with emphasis on next-generation sequencing technology and metagenomics．

Abstract:Abstract:［Objective］The diversity of culturable bacteria in the six frozen soils from High-latitude area and High-altitude area were analyzed by using culture-dependent approaches．［Methods］Three solidified media were used to isolate culturable bacteria． Bacterial 16S rRNA genes of the isolates were PCR amplified using bacteria-universal primers，and then were sequenced． The resulting bacterial 16S rRNA gene sequences were subjected to phylogenetic analysis．［Results］The abundance of culturable bacteria ranged from 4.70×103 to 2.57×105 colony forming units (CFU) per gram of soils (dry weight)． A total of 144 bacterial strains were obtained． The bacterial isolates from the High-latitude area were affiliated with three phyla (Firmicutes，Gammaproteobacteria，and Betaproteobacteria) with Pseudomonas，Bacillus，and Paenibacillus strains being dominant． The bacterial isolates from High-altitude area could be grouped into three different phyla (Gammaproteobacteria，Firmicutes，and Bacteroidetes) with Pseudomonas strains be dominant． ［Conclusion］The culturable bacteria are abundant and diverse in the frozen soils of High-latitude and High-altitude areas． The results also showed that the culturable bacterial community structure varied among different research areas．Our data have implications for a better understanding of culturable bacterial community in the frozen soils in China．

Abstract:Abstract:［Objective］ The purpose of this research is to isolate cold-adapted bacteria producing β-galactosidase from permafrost sediments of the bottom layer of the Glacier No．1 in the Tianshan Mountains，China．Physiological test and phylogenetic analysis were undertaken to expand our knowledge on diversity of psycrotrophic and psycrophlic bacteria．［Methods］By using lactose as the main carbon source and X-Gal as chromogenic agent in the medium，cold-adapted strains producing β-galactosidase were detected． Taxonomic identity and genetic diversity of strains isolated were determined by spatial 16S rRNA gene sequences and rep-PCR fingerprint．In addition，we analyzed the phonotypic differences between strains showing high similarity of 16S rRNA gene sequences， including the optimum growth temperature，salt tolerance，ability to use carbon source and antibiotic resistance spectra． ［Results］Of the total 90 coldadapted bacterial strains isolated，we found 25 stains with β-galactosidase activity，76% of which were Gram-positive bacteria． According to growth temperature range， 80% of strains producing β-galactosidase were identified as psychrophilic bacteria，20% as psychrotrophs． Phylogeneticlly，the β-galactosidase-producing bacterial isolates fell in four groups: subclasses α、β and γ of Proteobacteria，and Firmicutes phylum．［Conclusion］ The results enrich our knowledge on the phylogenetic and physiological diversity of cold-adapted strains producing β-galactosidase in cold environments．

Abstract:Abstract:［Objective］To determine the volatile components of mycelia of Isaria cateinannulata cultured under different culture conditions，and to analyze the relationships between the culture conditions and volatile metabolites．［Methods］Mycelia were cultured in solid plates with SDAY medium and liquid shake flasks with SDY medium．The culture conditions were at 25℃ and 8 days． Volatile components in the mycelia of I． cateinannulata were extracted with simultaneous distillation extraction and analyzed by gas chromatography-mass spectrometry． ［Result］Alkenes，alkanes，heterocyclic and polycyclic aromatic hydrocarbons( PAH) were existed abundantly both in the mycelia of liquid and solid cultures，but the kinds and relative concentrations of the volatile components in mycelia of liquid and solid cultures were very different． Forty-one compounds were identified from the mycelia of solid culture and 32 compounds were identified from the mycelia of liquid culture． Esters，quinones and oximes were only found in solid cultured mycelia whereas carboxylic acids were only discovered in the mycelia of liquid culture． At the same time，mycelia of liquid culture contained much more phenols． The most abundant compounds in mycelia of liquid and solid cultures were hydrocarbons．The volatile extracts of solid cultured mycelia contained 57. 6% alkenes and 9. 19% alkanes． The volatile extracts of liquid cultured mycelia contained 7. 85% alkenes and 22. 4% alkanes． ［Conclusion］ Liquid or solid culture conditions influenced the volatile components of mycelia of I． cateinannulata．

Abstract:Abstract:［Objective］To investigate the growth of Listeria monocytogenes (LM) in chilled pork at four temperature and to evaluate the accuracy of three predictive models- GP (Growth Predictor)，PMP(Pathogen Modeling Programme) and CP (ComBase Predictor) in predicting LM growth in chilled pork． ［Methods］ LM growth in chilled pork at 4℃，8℃，12℃ and 16℃ were determined by plate counting． The growth data were fitted by DMFit software to calculate related growth parameters: lag phase duration (LPD)，growth rate (GR) and maximum population density (MPD)．The observation values and predictions of the three different models were compared． ［Result］LM grew into exponential phase after 2. 6 hours of adaptation at 16℃ ． A four- degree increase from 8℃ to 12℃ doubled GR from 0.017 log(cfu/g)．h－1 to 0.038log(cfu/g)．h－1)．Over the temperature span from 4℃ to 16℃，GR values predicted by PMP were lower than observations，while those of LPD higher than observations． At temperature above 8℃ ，LPD values predicted by GP were higher than observations．Of three predictive models，GP prediction of GR was the best，though slightly higher than observations，with the bias factor (Bf) at 1.01 and accuracy factor (Af) at 1. 38，while CP was nearest to observations for LPD prediction，but still with high values of Af and Bf (4.33 and 2.83 respectively)．［Conclusion］ It is of utmost importance to control temperature in chilled pork production and distribution． Because of the conservative but unsafe predictions，PMP model is not suitable for prediction of LM in chilled pork． We suggest to use GP for GR prediction． CP may be used to predict LPD as a reference，but with caution．

Abstract:Abstract:［Objective］To compare volatile fatty acid (VFA) concentration and microbiota in faeces between healthy and diarrhoeal piglets．［Methods］ Fecal samples from healthy and diarrhoeal piglets were collected． VFA concentration was determined by GC analysis． Total bacterial DNA was extracted and used for molecular analysis of microbiota．［Results］As compared to healthy piglets，the concentration of acetate in feces of diarrhoeal piglets tended to increase，while branched chain fatty acid (BCFA) decreased significantly (p＜0.05)，total VFA (TVFA)，propionate and butyrate tended to decrease． The ratio of acetate to TVFA in faeces of diarrhoeal piglets was significantly higher than that in healthy piglets (p＜0.05)，while the ratio of propionate and BFVA to TVFA decreased significantly after diarrhoea (p＜0.05)．DGGE analysis of total bacterial community and Clostridium cluster Ⅳ group showed no significant changes in both bacterial community were found in faeces of piglets after diarrhoea． Similarity analysis of DGGE profiles revealed that faecal samples of diarrhoeal piglets tended to gather in the same cluster． Real-time PCR results showed that as compared to healthy piglets，the 16S rRNA gene copies of total bacteria and Clostridium cluster Ⅳ decreased significantly in faeces of piglets after Diarrhea(p＜0.05)，while there was no significant change in the numbers of E coli and Lactobacilli．［Conclusion］ VFA composition in faeces of diarrhoeal piglets changed accompanying with the shift of microbiota as compared to healthy piglets．

Abstract:Abstract:［Objective］ To investigate the diversity of bacteria in soft rot Chinese cabbage and analyze their correlation with rhizosphere bacteria，we analyzed the bacterial population structures of soft rot Chinese cabbage and the rhizosphere in different habitat．［Methods］ Based on the initial medium and artificial Chinese cabbage medium，we isolated the bacteria from soft rot tissues and rhizospheric soils from two typical habitats． According to the analysis of 16S rRNA gene sequence homology，we identified the isolated strains and analyzed the strains population structure．［Results］ The total bacteria in soft rot tissues were 4.0×108 cell g－1 and 1.2×1011 cell g－1，the number of pure strains were 56 and 85，the dominant strains were Curtobacterium flaccumfaciens pv．flaccumfaciens and Pseudomonas spp．(P．hibiscicola，P.taiwanensis，P.tuomuerensis，P.mosselii)．The total bacteria in rhizospheric soils were 2.7×105 cell g－1 and 6.2×107 cell g－1，the number of pure strains were 36 and 70，the dominant strains were Bacillus megatherium and Pseudomonas spp．(P．plecoglossicida，P．hibiscicola，P．parafulva，P．monteilii，P．geniculata)．［Conclusion］ The methods used in this study were effective in analyzing bacterial diversity in soft rot Chinese cabbage and the results correlated well with the soil bacteria analysis，suggesting that soft rot Chinese cabbage may be induced by various environmental bacteria． Our results infer that soft rot of Chinese cabbage might be pathogen-complex，and provide the clues for the mechanism study and protection．

Abstract:Abstract:［Objective］We separated，screened and identified a heterotrophic nitrifying and aerobic denitrifying bacterium from the surface sediment of a culture pool． Furthermore，we studied the role it plays in denitrification．［Methods］We separated the bacterium through enrichment culture，identified it by observing its morphological characteristics，studying its physiological and biochemical properties and making phylogenetic analysis of its 16S rDNA sequences． Then we studied the growth curve by regularly measuring the OD600 value，studied the influencing factors and optimum conditions of denitrification through orthogonal experiment，and examined its denitrification activity through interaction with the activated sludge of sewage treatment plant． ［Results］The strain was identified as Acinetobacter and named A．sp．YF14，which is the first known Acinetobacter that carries out heterotrophic nitrification and aerobic denitrification． It reached the logarithmic growth phase after 12 hours，the stationary phase after 22 hours，and the decline phase after 45 hours． Using strain YF14 in a reactor under heterotrophic conditions，the NH +4 -N and total nitrogen removal rates reached 92% and 91% respectively within 3 days． In addition，nitrate and nitrite nitrogen were not observed during the incubation． Under aerobic incubation conditions，almost all of the nitrogen was removed through denitrification in the nitrate or nitrite culture medium inoculated with strain YF14. The orthogonal experiment results indicated that the denitrification effect was optimal when the rotate speed，carbon source，inoculation percentages，carbon nitrogen ratio and pH were 160 r /min，glucose，1% ，8:1 and 6.5，respectively． Sorting Order of the factors on the denitrification effect was rotate speed ＞ inoculation percentages ＞ carbon source ＞ carbon nitrogen ratio ＞ pH． The strain YF14 could improve the denitrification rate by about 30% when interacting with active sludge．［Conclusion］The strain YF14 coupling of heterotrophic nitrification and aerobic denitrification is feasible and is of practical value in water treatment．

Abstract:Abstract:［Objective］To study the contribution of virulence genes of STEC O18 XZ113 isolate to the pathogenicity in mice．［Methods］The eaeA，stx2 and ehxA knock-out mutants of STEC strain XZ113 were generated using λ-Red recombination system． ［Results］Bacterial adherence test showed that the eaeA mutant adhered to HEp-2 cells in a diffuse manner with no microcolony formation． Vero cells assay showed that the stx mutant had no cytotoxicity to Vero cells．Enterohemolytic activity test showed that the ehxA mutant lost the ability to express the enterohemolytic activity．Competition assay between the wild-type strain XZ113 and its mutants in vivo and in vitro showed that all mutants were mildly attenuated in vitro，but in vivo，XZ113△eaeA was moderate attenuated，XZ113△stx2 and XZ113△ehxA were all highly attenuated．［Conclusions］ These results indicate that the virulence factors encoded by the stx2 and ehxA genes were important for the pathogenesis of STEC O18 in mice．

Abstract:Abstract:［Objective］ It was reported that subgroup J avian leukosis virus strain NX0101 activates PI3K /Akt pathway during early infection in DF-1 cells． Whether there is YXXM motif in the amino acid sequence of NX0101 and the function of YXXM motif were studied．［Methods］ The presence of internal transmembrane domains in the envelope protein of NX0101 was analyzed by Tmpred． Point mutation was introduced to change the YXXM motif in the NX0101 strain to FXXA． The plasmid containing the full genome of NX0101 with mutation within the YXXM motif in pMD18-T vector was constructed and transfected into DF-1 cells． Viral replication levels of NX0101 strain and the mutation one were tested and compared by real-time PCR and ELISA． ［Results］ The amino acid sequence of NX0101 strain had one YXXM motif (amino acids 554－557) in the cytoplasmic tail of envelope protein． The mutated NX0101 strain (Y554F，M557A) was rescued by reverse genetics technique． Viral replication of the mutated NX0101 strain was significantly lower than that of NX0101 strain in the level of either RNA or protein synthesis．［Conclusion］ The results revealed that theYXXM motif was important for virus NX0101 replication in DF-1 cells．

Abstract:Abstract: ［Objective］ In the present study，we aim to evaluate the inhibitory effect of aflatoxin on Vibrio fischeri luminescence．［Methods］ V． fischeri culture is treated with aflatoxin or the culture broth of aflatoxin-producing strains，and the luminescence intensity of V． fischeri is detected to analyze the influence of aflatoxin on V． fischeri．［Results］The logarithmic value of aflatoxin concentration and the decrease ratio of V． fischeri luminescence is in a linear relationship．Based on the regression equation between aflatoxin concentration and luminescence decrease of V． fischeri，the toxinproducing status of different microbes can be detected quickly and exactly: all of six tested Aspergillus flavus strains show toxigenicity to V．fischeri，and their toxin yield reached 14. 94 mg/L－46.45 mg/L (represented by aflatoxin concentration)，while the tested Aspergillus oryzae shows no toxigenicity． ［Conclusion］ The above data showed that the luminescence change of V． fischeri could exactly reflect the capability of various microbes to produce toxin (especially aflatoxin)，which provided a new clue for rapid detection of aflatoxin in industrial and agricultural production and could bedeveloped as a potential method for aflatoxin assay．

Abstract:Abstract:［Objective］ In order to discover novel antimicrobial peptides against important crop pathogens，we designed and screened a high capacity random peptide library and isolated a number of clones expressing peptides with antifungal activity． We selected 96 peptides from the library and synthesized their sequence，which were used to assay their activity against crop fungal pathogens．［Methods］ Using agar diffusion assay，these peptides were assayed for their activity against pathogens that cause cotton Fusarium wilt (Fusarium f．sp．vasinfecum)，cotton red rot (Fusarium moniliforme)，wheat spot blotch (Bipolaris sorokiniana) and potato early blight (Alternaria solani)．［Results］ The three random peptides，A6，D4 and F10，showed the strongest activity against the above four crop fungal pathogens． Through Blastp analysis，we did not find they have homologous sequences with known antimicrobial peptides． ［Conclusion］ The novelantimicrobial peptides will provide gene resources for preventing important crop pathogens．