Background Salmonella Typhimurium challenge causes a huge detriment to chicken production.N-acyl homoserine lactonase(AHLase),a quorum quenching enzyme,potentially inhibits the growth and virulence of Gram-negative ba...Background Salmonella Typhimurium challenge causes a huge detriment to chicken production.N-acyl homoserine lactonase(AHLase),a quorum quenching enzyme,potentially inhibits the growth and virulence of Gram-negative bacteria.However,it is unknown whether AHLase can protect chickens against S.Typhimurium challenge.This study aimed to evaluate the effects of AHLase on growth performance and intestinal health in broilers challenged by S.Typhimurium.A total of 240 one-day-old female crossbred broilers(817C)were randomly divided into 5 groups(6 replicates/group):negative control(NC),positive control(PC),and PC group supplemented with 5,10 or 20 U/g AHLase.All birds except those in NC were challenged with S.Typhimurium from 7 to 9 days of age.All parameters related to growth and intestinal health were determined on d 10 and 14.Results The reductions(P<0.05)in body weight(BW)and average daily gain(ADG)in challenged birds were alleviated by AHLase addition especially at 10 U/g.Thus,samples from NC,PC and PC plus 10 U/g AHLase group were selected for further analysis.S.Typhimurium challenge impaired(P<0.05)intestinal morphology,elevated(P<0.05)ileal inflammatory cytokines(IL-1βand IL-8)expression,and increased(P<0.05)serum diamine oxidase(DAO)activity on d 10.However,AHLase addition normalized these changes.Gut microbiota analysis on d 10 showed that AHLase reversed the reductions(P<0.05)in several beneficial bacteria(e.g.Bacilli,Bacillales and Lactobacillales),along with increases(P<0.05)in certain harmful bacteria(e.g.Proteobacteria,Gammaproteobacteria,Enterobacteriaceae and Escherichia/Shigel a)in PC group.Furthermore,AHLase-induced increased beneficial bacteria and decreased harmful bacteria were basically negatively correlated(P<0.05)with the reductions of ileal IL-1βand IL-8 expression and serum DAO activity,but positively correlated(P<0.05)with the increased BW and ADG.Functional prediction revealed that AHLase abolished S.Typhimurium-induced upregulations(P<0.05)of certain pathogenicity-related pathways such as lipopolysaccharide biosynthesis,shigellosis,bacterial invasion of epithelial cells and pathogenic Escherichia coli infection of gut microbiota.Conclusions Supplemental AHLase attenuated S.Typhimurium-induced growth retardation and intestinal disruption in broilers,which could be associated with the observed recovery of gut microbiota dysbiosis.展开更多
Bacterial cells rely on signaling molecules to communicate with others from the same species and induce certain genes in a process known as quorum sensing (QS). A common molecule is N-acyl homoserine lactone (AHL) whi...Bacterial cells rely on signaling molecules to communicate with others from the same species and induce certain genes in a process known as quorum sensing (QS). A common molecule is N-acyl homoserine lactone (AHL) which is responsible for the expression of virulence and other factors that allow the organisms to compete in a given environment. On the other hand, other bacteria produce certain enzymes such as AHL-lactonase that break down AHL molecules and prevent gene expression of these factors. The aim of this work was to examine the level of degradation of AHL molecules by AHL-lactonase in 62 Bacillus thuringiensis (Bt) strains isolated from Middle Tennessee, Mississippi, and Alabama. N-hexanoyl-homoserine lactone (C<sub>6</sub>-HSL) and N-3-oxo-hexanoyl homoserine lactone (3-oxo-C<sub>6</sub>-HSL), which cause Chromobacterium violaceum (CV026) to produce a purple pigment were tested at different concentrations to view the Bt lactonase activity. In addition, PCR was used to test for the presence of the lactonase gene. The results showed that among the 62 Bt strains, there were 58 that possessed the AHL-lactonase (aiiA) gene and 48 strains were able to degrade C<sub>6</sub>-HSL. At high concentrations of AHL, only 13 strains were able to completely degrade C6-HSL. In addition, degradation of 3-oxo-C<sub>6</sub>-HSL was weak compared to C<sub>6</sub>-HSL. The results also revealed that AHL lactonase was thermostable, and it was concluded that the level of degradation varies in Bt strains. Only 13 of the strains studied have potent inhibitory activity against C<sub>6</sub>-HSL, which may be good to be used in field applications to control agricultural pest.展开更多
The reactions of 5-methyl-3-hydroxyisoxazole with 2, 2-dimethyl, 3-substituted cyclopropanecarboxylic chlorides give O-acyl-5-methyl-3-hydroxyisoxazole and N-acyl-5-methylisoxazolin-3-one derivatives. The ratio of O-a...The reactions of 5-methyl-3-hydroxyisoxazole with 2, 2-dimethyl, 3-substituted cyclopropanecarboxylic chlorides give O-acyl-5-methyl-3-hydroxyisoxazole and N-acyl-5-methylisoxazolin-3-one derivatives. The ratio of O-acyl to N-acyl product depends upon the acylation reagents. O-acyl derivatives can be converted to the N-acyl compounds by isomerization under acidic conditions or heating.展开更多
The aim of this research was to detect the N-acyl homoserine lactones (AHLs) production and QseB/C gene of Aeromonas hydrophila. We analyzed the potentials of these isolates of Aeromonas hydrophila in causing biofilm ...The aim of this research was to detect the N-acyl homoserine lactones (AHLs) production and QseB/C gene of Aeromonas hydrophila. We analyzed the potentials of these isolates of Aeromonas hydrophila in causing biofilm formation, hemolysis, protease, and lipase. The antibiotic susceptibility of the 15 Aeromonas hydrophila isolates was also investigated. The detection of AHLs was carried out using the Chromobacterium violaceum strain CV026 as biosensors. The isolated strains were tested for the reaction of C. violaceum CV026 by cross-streaking on an agar plate. Production of AHLs was determined by the diffusing via the agar plates and the tinge of the biosensor strains. All isolated strains produced AHLs. A polymerase chain reaction (PCR) showed the isolated strains had qseB and qseC genes. Susceptibility tests of A. hydrophila isolates were administered against 25 different antibiotic disks representing 12 classes of antibiotics. The strains were highly resistant to β-Lactam with 96.7% showing resistibility, whereas 97.7% susceptibility was found towards Aminoglycoside class of the antibiotic used. 60% showed intermediate resistant to Polypeptide. 100% of the strains showed no resistant to Aminoglycoside, Polypeptide, Monobactam, and Carbapenems class of antibiotics. Each of the isolates was found to be associated with at least one virulent factor. Our results clearly demonstrated that there is a presence of QseB/C genes in A. hydrophila and also produces AHLs molecule and virulence factors. The investigated isolates showed the pathogenic potential of Aeromonas hydrophila which makes it a serious threat to public health.展开更多
This study aimed to investigate the potential mitigating effects of N-acyl homoserine lactonase(AHLase)on the virulence of Salmonella typhimurium and its induction of intestinal damages in broilers.In vitro study was ...This study aimed to investigate the potential mitigating effects of N-acyl homoserine lactonase(AHLase)on the virulence of Salmonella typhimurium and its induction of intestinal damages in broilers.In vitro study was firstly conducted to examine if AHLase treatment could attenuate the virulence of S.typhimurium.Then,an in vivo experiment was performed by allocating 240 broiler chicks at 1 d old into 3 groups(8 replicates per group):negative control(NC),positive control(PC),and PC supplemented with 10,000 U/kg AHLase.All chicks except those in NC were orally challenged by S.typhimurium from 8to 10 d of age.Parameters were measured on d 11 and 21.The results showed that treatment with 1 U/mL AHLase suppressed the biofilm-forming ability(including biofilm biomass,extracellular DNA secretion and biofilm formation-related gene expression),together with swarming motility and adhesive capacity of S.typhimurium.Supplemental 10,000 U/kg AHLase counteracted S.typhimurium-induced impairments(P<0.05)in broiler growth performance(including final body weight,average daily gain and average daily feed intake)during either 1-11 d or 12-21 d,and increases(P<0.05)in the indexes of liver,spleen and bursa of Fabricius on d 11,together with reductions(P<0.05)in ileal villus height and its ratio to crypt depth on both d 11 and 21.AHLase addition also normalized the increased(P<0.05)m RNA expression of ileal occludin on both d 11 and 21 in S.typhimurium-challenged broilers.However,neither S.typhimurium challenge nor AHLase addition altered(P>0.05)serum diamine oxidase activity of broilers.Noticeably,S.typhimurium challenge caused little change in the mRNA expression of ileal inflammatory cytokines except for an increase(P<0.05)in interleukin-8 expression on d 11,whereas AHLase addition normalized(P<0.05)this change.In conclusion,AHLase treatment could attenuate the virulence and pathogenicity of S.typhimurium,thus contributing to alleviate S.typhimurium-induced growth retardation and intestinal damages in broilers.展开更多
N-acyl-homoserine lactones(AHLs) serve as quorum-sensing signals, which control a number of bacterial processes in many proteobacteria. Here we report the effects of exogenous short-chain AHL on the denitrifying proce...N-acyl-homoserine lactones(AHLs) serve as quorum-sensing signals, which control a number of bacterial processes in many proteobacteria. Here we report the effects of exogenous short-chain AHL on the denitrifying process of Paracoccus denitrificans, which are capable of aerobic and anaerobic growth by utilizing nitrate. The denitrification activity of these cells was monitored by measuring denitrification products(including nitrate, nitrite,and nitrous oxide), and the individual messenger ribonucleic acid(m RNA) levels of nitrate,nitrite, nitric oxide and nitrous oxide reductases. The results indicated that 2 μmol/L C6-homoserine lactone(HSL) has little effect on cell density under either anaerobic or aerobic culture conditions, and the nitrate reduction activity appeared slightly affected by N-hexanoyl-DL-homoserine lactone(C6-HSL). However, exogenous C6-HSL significantly affected the transcription of nitrite reductase and nitric oxide reductase genes in P.denitrificans regardless of the presence of oxygen, and N_2O accumulation activity in P. denitrificans was suppressed by C6-HSL under aerobic condition. In contrast, exogenous C6-HSL stimulated the production of N_2O under anaerobic condition, suggesting that the regulation of denitrification by quorum sensing may be important in N_2O release.展开更多
Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combinin...Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm-1, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm-1 and two baseline methods, the most suitable ratios Aprobe band/Areference band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to be A1560/A2880, A1560/A2920 and A1655/A3430(A1560/A2880 is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm-1 bands. The determination range of the D.D. (1%-100%) covered almost the whole range. The standard curves with A1560/A2880 and A1655/A3430 were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-propionyl chitosan, N-butyryl chitosan and N-hexanoyl chitosan.展开更多
A new Staudinger strategy entails a unique C-P bond cleavage,instead of N-P bond cleavage,during the construction of N-acyl phosphinamidites by using acyl-phosphine substrates.The reaction is performed under very mild...A new Staudinger strategy entails a unique C-P bond cleavage,instead of N-P bond cleavage,during the construction of N-acyl phosphinamidites by using acyl-phosphine substrates.The reaction is performed under very mild conditions,with no need for additional catalysts or additives,and thus preserves stereogenic centers that are sensitive to epimerization.A range of novel N-acyl phosphinamidites,including those bearing a chiral amino acid skeleton and axial chirality as well as complex natural product scaffolds,were produced with N_(2) gas as the only byproduct.These N-acyl phosphinamidites are potential novel P-O ligands,and preliminary screening results have demonstrated their application as chiral organic catalysts.展开更多
The present study investigated the relationship between N-acyl-homoserine lactone(AHL)-based quorum sensing(QS) and the physico-chemical properties of aerobic granules.Stable mature granules were observed in SBR2 and ...The present study investigated the relationship between N-acyl-homoserine lactone(AHL)-based quorum sensing(QS) and the physico-chemical properties of aerobic granules.Stable mature granules were observed in SBR2 and SBR3 with average diameters of 0.96,and1.49 mm,respectively. The sludge densities of aerobic granules in SBR2 and SBR3 were1.0246,and 1.0201 g/mL,respectively,which were higher than that of flocculent sludge in SBR1(1.0065 g/mL). The results showed that the activity of AHL-based QS in SBR2 and SBR3 amounted to 2.4- and 2.1-fold induction,however,that in SBR1 with flocculent sludge was1.6-fold induction. In addition,the results also showed that the activity of AHL-based QS in the three reactors rose in the feast condition,and then dropped with the consumption of substrate. However,the activity of AHL-based QS in these three reactors recovered again in prolonged starvation. Furthermore,the results showed that the enhancement of AHL-based QS favored the extracellular polymeric substance production of microorganisms in activated sludge. Thus,it could be concluded that aerobic granules showed higher AHL-based QS than flocculent sludge,which resulted from the higher sludge density of aerobic granules than flocculent sludge. AHL-based QS was related to the metabolism energy in the feast condition; however,in prolonged starvation,microorganisms would emit more AHL-like molecules to protect themselves to resist starvation. Moreover,the enhancement of AHL-based QS favored the EPS component productivity of the microorganisms in activated sludge,which contributed to maintain the aerobic granular structure.展开更多
The aim of this work was to inhibit biofilm formation by taking advantages of bacterial surface display technology in combination with cell membrane chromatography.A recombinant protein INPAidH was constructed by fusi...The aim of this work was to inhibit biofilm formation by taking advantages of bacterial surface display technology in combination with cell membrane chromatography.A recombinant protein INPAidH was constructed by fusing a quorum signal hydrolase AidH to the C-terminus of the ice nucleation protein(INP).Expression of INP-AidH was achieved on E.coli cell surface at an expression level of 30%of total membrane proteins.Activity of INP-AidH on cell membranes was confirmed in degrading the quorum signal C6-HSL as well as inhibiting bacterial biofilm.Immobilization of INP-AidH anchored cell membranes on silica gel particles was facilitated by taking advantages of cell membrane chromatography.The functionalized silica gel particles also exhibit activities in degrading C6-HSL and inhibiting bacterial biofilm.This article presents a new approach to prevent biofilm formation of silica-based materials.展开更多
基金financially supported by the National Natural Science Foundation of China(No.31872390)the Modern Feed Industry Innovation Team Project of Guangdong Province(No.2021KJ115)。
文摘Background Salmonella Typhimurium challenge causes a huge detriment to chicken production.N-acyl homoserine lactonase(AHLase),a quorum quenching enzyme,potentially inhibits the growth and virulence of Gram-negative bacteria.However,it is unknown whether AHLase can protect chickens against S.Typhimurium challenge.This study aimed to evaluate the effects of AHLase on growth performance and intestinal health in broilers challenged by S.Typhimurium.A total of 240 one-day-old female crossbred broilers(817C)were randomly divided into 5 groups(6 replicates/group):negative control(NC),positive control(PC),and PC group supplemented with 5,10 or 20 U/g AHLase.All birds except those in NC were challenged with S.Typhimurium from 7 to 9 days of age.All parameters related to growth and intestinal health were determined on d 10 and 14.Results The reductions(P<0.05)in body weight(BW)and average daily gain(ADG)in challenged birds were alleviated by AHLase addition especially at 10 U/g.Thus,samples from NC,PC and PC plus 10 U/g AHLase group were selected for further analysis.S.Typhimurium challenge impaired(P<0.05)intestinal morphology,elevated(P<0.05)ileal inflammatory cytokines(IL-1βand IL-8)expression,and increased(P<0.05)serum diamine oxidase(DAO)activity on d 10.However,AHLase addition normalized these changes.Gut microbiota analysis on d 10 showed that AHLase reversed the reductions(P<0.05)in several beneficial bacteria(e.g.Bacilli,Bacillales and Lactobacillales),along with increases(P<0.05)in certain harmful bacteria(e.g.Proteobacteria,Gammaproteobacteria,Enterobacteriaceae and Escherichia/Shigel a)in PC group.Furthermore,AHLase-induced increased beneficial bacteria and decreased harmful bacteria were basically negatively correlated(P<0.05)with the reductions of ileal IL-1βand IL-8 expression and serum DAO activity,but positively correlated(P<0.05)with the increased BW and ADG.Functional prediction revealed that AHLase abolished S.Typhimurium-induced upregulations(P<0.05)of certain pathogenicity-related pathways such as lipopolysaccharide biosynthesis,shigellosis,bacterial invasion of epithelial cells and pathogenic Escherichia coli infection of gut microbiota.Conclusions Supplemental AHLase attenuated S.Typhimurium-induced growth retardation and intestinal disruption in broilers,which could be associated with the observed recovery of gut microbiota dysbiosis.
文摘Bacterial cells rely on signaling molecules to communicate with others from the same species and induce certain genes in a process known as quorum sensing (QS). A common molecule is N-acyl homoserine lactone (AHL) which is responsible for the expression of virulence and other factors that allow the organisms to compete in a given environment. On the other hand, other bacteria produce certain enzymes such as AHL-lactonase that break down AHL molecules and prevent gene expression of these factors. The aim of this work was to examine the level of degradation of AHL molecules by AHL-lactonase in 62 Bacillus thuringiensis (Bt) strains isolated from Middle Tennessee, Mississippi, and Alabama. N-hexanoyl-homoserine lactone (C<sub>6</sub>-HSL) and N-3-oxo-hexanoyl homoserine lactone (3-oxo-C<sub>6</sub>-HSL), which cause Chromobacterium violaceum (CV026) to produce a purple pigment were tested at different concentrations to view the Bt lactonase activity. In addition, PCR was used to test for the presence of the lactonase gene. The results showed that among the 62 Bt strains, there were 58 that possessed the AHL-lactonase (aiiA) gene and 48 strains were able to degrade C<sub>6</sub>-HSL. At high concentrations of AHL, only 13 strains were able to completely degrade C6-HSL. In addition, degradation of 3-oxo-C<sub>6</sub>-HSL was weak compared to C<sub>6</sub>-HSL. The results also revealed that AHL lactonase was thermostable, and it was concluded that the level of degradation varies in Bt strains. Only 13 of the strains studied have potent inhibitory activity against C<sub>6</sub>-HSL, which may be good to be used in field applications to control agricultural pest.
基金Supposed by the National Natural Science Foundation of China
文摘The reactions of 5-methyl-3-hydroxyisoxazole with 2, 2-dimethyl, 3-substituted cyclopropanecarboxylic chlorides give O-acyl-5-methyl-3-hydroxyisoxazole and N-acyl-5-methylisoxazolin-3-one derivatives. The ratio of O-acyl to N-acyl product depends upon the acylation reagents. O-acyl derivatives can be converted to the N-acyl compounds by isomerization under acidic conditions or heating.
文摘The aim of this research was to detect the N-acyl homoserine lactones (AHLs) production and QseB/C gene of Aeromonas hydrophila. We analyzed the potentials of these isolates of Aeromonas hydrophila in causing biofilm formation, hemolysis, protease, and lipase. The antibiotic susceptibility of the 15 Aeromonas hydrophila isolates was also investigated. The detection of AHLs was carried out using the Chromobacterium violaceum strain CV026 as biosensors. The isolated strains were tested for the reaction of C. violaceum CV026 by cross-streaking on an agar plate. Production of AHLs was determined by the diffusing via the agar plates and the tinge of the biosensor strains. All isolated strains produced AHLs. A polymerase chain reaction (PCR) showed the isolated strains had qseB and qseC genes. Susceptibility tests of A. hydrophila isolates were administered against 25 different antibiotic disks representing 12 classes of antibiotics. The strains were highly resistant to β-Lactam with 96.7% showing resistibility, whereas 97.7% susceptibility was found towards Aminoglycoside class of the antibiotic used. 60% showed intermediate resistant to Polypeptide. 100% of the strains showed no resistant to Aminoglycoside, Polypeptide, Monobactam, and Carbapenems class of antibiotics. Each of the isolates was found to be associated with at least one virulent factor. Our results clearly demonstrated that there is a presence of QseB/C genes in A. hydrophila and also produces AHLs molecule and virulence factors. The investigated isolates showed the pathogenic potential of Aeromonas hydrophila which makes it a serious threat to public health.
基金financially supported by the National Natural Science Foundation of China(No.32102584)the Modern Feed Industry Innovation Team Project of Guangdong Province(No.2021KJ115)。
文摘This study aimed to investigate the potential mitigating effects of N-acyl homoserine lactonase(AHLase)on the virulence of Salmonella typhimurium and its induction of intestinal damages in broilers.In vitro study was firstly conducted to examine if AHLase treatment could attenuate the virulence of S.typhimurium.Then,an in vivo experiment was performed by allocating 240 broiler chicks at 1 d old into 3 groups(8 replicates per group):negative control(NC),positive control(PC),and PC supplemented with 10,000 U/kg AHLase.All chicks except those in NC were orally challenged by S.typhimurium from 8to 10 d of age.Parameters were measured on d 11 and 21.The results showed that treatment with 1 U/mL AHLase suppressed the biofilm-forming ability(including biofilm biomass,extracellular DNA secretion and biofilm formation-related gene expression),together with swarming motility and adhesive capacity of S.typhimurium.Supplemental 10,000 U/kg AHLase counteracted S.typhimurium-induced impairments(P<0.05)in broiler growth performance(including final body weight,average daily gain and average daily feed intake)during either 1-11 d or 12-21 d,and increases(P<0.05)in the indexes of liver,spleen and bursa of Fabricius on d 11,together with reductions(P<0.05)in ileal villus height and its ratio to crypt depth on both d 11 and 21.AHLase addition also normalized the increased(P<0.05)m RNA expression of ileal occludin on both d 11 and 21 in S.typhimurium-challenged broilers.However,neither S.typhimurium challenge nor AHLase addition altered(P>0.05)serum diamine oxidase activity of broilers.Noticeably,S.typhimurium challenge caused little change in the mRNA expression of ileal inflammatory cytokines except for an increase(P<0.05)in interleukin-8 expression on d 11,whereas AHLase addition normalized(P<0.05)this change.In conclusion,AHLase treatment could attenuate the virulence and pathogenicity of S.typhimurium,thus contributing to alleviate S.typhimurium-induced growth retardation and intestinal damages in broilers.
基金supported by the National Natural Science Foundation of China(Nos.41371266,41501250,21377157)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB15030101)
文摘N-acyl-homoserine lactones(AHLs) serve as quorum-sensing signals, which control a number of bacterial processes in many proteobacteria. Here we report the effects of exogenous short-chain AHL on the denitrifying process of Paracoccus denitrificans, which are capable of aerobic and anaerobic growth by utilizing nitrate. The denitrification activity of these cells was monitored by measuring denitrification products(including nitrate, nitrite,and nitrous oxide), and the individual messenger ribonucleic acid(m RNA) levels of nitrate,nitrite, nitric oxide and nitrous oxide reductases. The results indicated that 2 μmol/L C6-homoserine lactone(HSL) has little effect on cell density under either anaerobic or aerobic culture conditions, and the nitrate reduction activity appeared slightly affected by N-hexanoyl-DL-homoserine lactone(C6-HSL). However, exogenous C6-HSL significantly affected the transcription of nitrite reductase and nitric oxide reductase genes in P.denitrificans regardless of the presence of oxygen, and N_2O accumulation activity in P. denitrificans was suppressed by C6-HSL under aerobic condition. In contrast, exogenous C6-HSL stimulated the production of N_2O under anaerobic condition, suggesting that the regulation of denitrification by quorum sensing may be important in N_2O release.
基金the National Natural Science Foundation of China (Grant No. 29974023) and the Natural Science Foundation of Fujian Province, China (Grant No. Z9910006).
文摘Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm-1, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm-1 and two baseline methods, the most suitable ratios Aprobe band/Areference band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to be A1560/A2880, A1560/A2920 and A1655/A3430(A1560/A2880 is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm-1 bands. The determination range of the D.D. (1%-100%) covered almost the whole range. The standard curves with A1560/A2880 and A1655/A3430 were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-propionyl chitosan, N-butyryl chitosan and N-hexanoyl chitosan.
文摘A new Staudinger strategy entails a unique C-P bond cleavage,instead of N-P bond cleavage,during the construction of N-acyl phosphinamidites by using acyl-phosphine substrates.The reaction is performed under very mild conditions,with no need for additional catalysts or additives,and thus preserves stereogenic centers that are sensitive to epimerization.A range of novel N-acyl phosphinamidites,including those bearing a chiral amino acid skeleton and axial chirality as well as complex natural product scaffolds,were produced with N_(2) gas as the only byproduct.These N-acyl phosphinamidites are potential novel P-O ligands,and preliminary screening results have demonstrated their application as chiral organic catalysts.
基金supported by the National Natural Science Found of China (No.51078036)
文摘The present study investigated the relationship between N-acyl-homoserine lactone(AHL)-based quorum sensing(QS) and the physico-chemical properties of aerobic granules.Stable mature granules were observed in SBR2 and SBR3 with average diameters of 0.96,and1.49 mm,respectively. The sludge densities of aerobic granules in SBR2 and SBR3 were1.0246,and 1.0201 g/mL,respectively,which were higher than that of flocculent sludge in SBR1(1.0065 g/mL). The results showed that the activity of AHL-based QS in SBR2 and SBR3 amounted to 2.4- and 2.1-fold induction,however,that in SBR1 with flocculent sludge was1.6-fold induction. In addition,the results also showed that the activity of AHL-based QS in the three reactors rose in the feast condition,and then dropped with the consumption of substrate. However,the activity of AHL-based QS in these three reactors recovered again in prolonged starvation. Furthermore,the results showed that the enhancement of AHL-based QS favored the extracellular polymeric substance production of microorganisms in activated sludge. Thus,it could be concluded that aerobic granules showed higher AHL-based QS than flocculent sludge,which resulted from the higher sludge density of aerobic granules than flocculent sludge. AHL-based QS was related to the metabolism energy in the feast condition; however,in prolonged starvation,microorganisms would emit more AHL-like molecules to protect themselves to resist starvation. Moreover,the enhancement of AHL-based QS favored the EPS component productivity of the microorganisms in activated sludge,which contributed to maintain the aerobic granular structure.
基金Funded by the National Natural Science Foundation of China(No.31771032)。
文摘The aim of this work was to inhibit biofilm formation by taking advantages of bacterial surface display technology in combination with cell membrane chromatography.A recombinant protein INPAidH was constructed by fusing a quorum signal hydrolase AidH to the C-terminus of the ice nucleation protein(INP).Expression of INP-AidH was achieved on E.coli cell surface at an expression level of 30%of total membrane proteins.Activity of INP-AidH on cell membranes was confirmed in degrading the quorum signal C6-HSL as well as inhibiting bacterial biofilm.Immobilization of INP-AidH anchored cell membranes on silica gel particles was facilitated by taking advantages of cell membrane chromatography.The functionalized silica gel particles also exhibit activities in degrading C6-HSL and inhibiting bacterial biofilm.This article presents a new approach to prevent biofilm formation of silica-based materials.
