绿脓杆菌Pseudomonas aeruginosa BTE-1直接电催化特征

本文研究厌氧条件下产电绿脓杆菌P. aeruginosa BTE-1的电化学催化特征。研究结果表明,P. aeruginosa BTE-1菌株在厌氧条件下,不能分泌可充当电子介体的绿脓菌素,但可通过在电极表面形成生物膜呈现了直接电催化性能。P. aeruginosa BTE-1在电极表面形成生物膜与其在特定电极电位下向电极传递电子的过程直接相关,适宜的电位为+0.2 V (vs. SCE),电位过高可能会损害P. aeruginosa BTE-1细胞。室温范围内升高温度可增强P. aeruginosa BTE-1生物膜电催化活性,但过高的温度(>60℃)会抑制生物膜电催化活性。循环伏安曲线显示,在厌氧条件下形成的P. aeruginosa BTE-1生物膜,具有与典型产电菌株G. sulfurreducens相近的氧化还原电位(-0.4 V~ -0.2 V vs. SCE)。P. aeruginosa BTE-1生物膜可电催化酵母抽取物和葡萄糖,但不能电催化醋酸盐。     

Stir-bar-sorptive extraction,with in-situ deconjugation,and thermal desorption with in-tube silylation,followed by gas chromatography-mass spectrometry for measurement of urinary 4-nonylphenol and 4-<Emphasis Type="Italic">tert</Emphasis>-octylphenol glucuronides

Bacterial quorum-sensing regulatory systems can be summarized in a simple model wherein an autoinducer molecule accumulates in cultures and stimulates regulatory changes in gene expression upon reaching a critical threshold concentration. Although quorum sensing was originally thought to be an isolated phenomenon governing the regulation of a handful of processes in only a few bacteria, it is now considered to be a widespread mechanism for coordinating bacterial gene expression. Over decades of research, investigations of autoinducer-mediated regulation have revealed that these systems are far more complicated than originally appreciated, and such discoveries have accelerated recently with the application of molecular and genomic tools. The focus of this review is to highlight recent advances describing complexities that go beyond the simple model of quorum sensing. These complexities include the regulation of autoinducer production and degradation, the presence of multiple quorum-sensing systems in individual bacteria that regulate diverse genes, often in coordination with other regulatory elements, and the influence of interorganismal interactions on quorum sensing.     

芳樟醇对莓实假单胞菌的抑菌活性及机制

食品在生产、运输和贮藏过程中易受致病菌污染而引起食源性疾病。芳樟醇具有抗菌作用,但其作用机制尚不明确。研究芳樟醇对莓实假单胞菌的抑菌活性及作用机制,可为其作为天然食品防腐剂的开发提供理论依据。通过测定最小抑菌浓度、绘制细菌生长曲线评价芳樟醇的抑菌活性;通过扫描电子显微镜观察、结晶紫染色实验、二乙酸荧光素染色实验以及测定电导率、核酸泄漏、呼吸代谢活力和呼吸链脱氢酶活性的变化探究芳樟醇的抑菌机制。结果表明:芳樟醇对莓实假单胞菌具有较强的抑制作用,最小抑菌浓度为1.5mL/L;芳樟醇能破坏莓实假单胞菌细胞的结构形态和细胞膜的完整性,增加细胞膜的通透性,导致胞内物质泄漏、膜外电导率升高;能抑制呼吸代谢活力和呼吸链脱氢酶活性,破坏呼吸链,导致胞内代谢紊乱。研究认为,芳樟醇可通过破坏莓实假单胞菌的细胞结构和抑制其呼吸代谢而发挥抑菌作用,有望作为天然防腐剂应用于食品的防腐保鲜。     

假单孢菌PKE117木素过氧化物酶的酶学性质及基因克隆

对纯化得到的假单孢菌PKE117的胞外木素过氧化物酶的酶学性质进行了初步研究,发现其最适pH为5.0,最适温度为30℃,以藜芦醇为底物,在25℃,pH3.0的琥珀酸钠缓冲液中与底物反应时的Km值为(0.277±0.0008)mmol/L,vmax为(0.049±0.001)mmol.mg-1protein.min-1。根据LiP已知保守序列设计引物,提取质粒,扩增得到一条199bp的DNA片段lip1和一条563bp的DNA片段lip2,序列比对结果显示与已报道的白腐真菌过氧化物酶基因的同源性不是很高。核苷酸翻译后的氨基酸序列比对结果发现,LiP1与Pycnoporus sanguineus的漆酶的同源性达到100%,与Mycobacteriumbovis的木素过氧化物酶的同源性达到80%;LiP2与Arabidopsis thaliana的过氧化物酶同源性达到100%,与Hordeum vulgare的过氧化物酶1同源性为75%。     

Polysaccharide differences between planktonic and biofilm-associated EPS from Pseudomonas fluorescens B52

The polysaccharides associated with free (planktonic) and surface-attached (biofilm) cells from cultures of Pseudomonas fluorescens strain B52 were compared. Variations in the attached matrix due to surface material (glass or stainless steel) were also analyzed. Two digestion methods were used to optimize the recoveries of sugars, uronic acids and acidic substituents. The yield of analyzable material after digestion reached 90% for the material associated to the biofilms, though only 20–30% for that bound to planktonic cells. The polysaccharide(s) in the biofilm had glucuronic and guluronic acids as main components, besides rhamnose, glucose and glucosamine. The proportion of glucuronic to guluronic acid was higher in the polysaccharide(s) found in biofilms formed on stainless steel than in those on glass.     

Influence of sialic acid and bacterial sialidase on differential adhesion of Pseudomonas aeruginosa to epithelial cells

Epithelial cell lines from several tissues show a differential sensitivity to Pseudomonas aeruginosa adherence. A549 (lung), HepG2 (liver) and Caco-2 (colon) cells presented an adhesion index of about 3, 1.5 and 5 CFU/cell, respectively, whereas Mz-Ch cell lines (gallbladder cholangiocytes) presented adhesion indexes up to 35. These variations could be associated with the variable amount of sialic acid in cell surface glycoconjugates. Moreover, the presence of free sialic acid in culture media induces the secretion by P. aeruginosa of a sialidase which is able to hydrolyze glycoconjugate-linked sialic acid. As shown with A549 cells, this specific hydrolysis increases bacterial adhesion, probably by unmasking new binding sites onto the cell surface.     

荧光假单胞菌株SE-6产铁载体的发酵条件

在摇瓶发酵条件下,研究了荧光假单胞菌SE-6在各种培养条件下的铁载体分泌量,确定了适合铁载体分泌的最佳培养条件：起始pH6．5,装瓶量200／500（mL）,接种量2％,最佳培养时间为46h左右,Fe^3＋浓度为0．8mg／L．在此条件下,铁载体在发酵液中含量最高,为大规模的发酵提供了有价值的数据．     

Biphenyl-cis-diol chemistry to access enantiopure aryl-substituted organoiron complexes

The endo face selectivity of the complexation of the biologically derived 3-phenyl-1,2-dihydroxycyclohexa-3,5-diene ligand has been proved by an X-ray crystallographic study of the enantiopure (1R,2S,3S) η⁴ tricarbonyliron complex, and the correlation between the absolute configuration of the complex and its circular dichroism curve has been established to provide a basis on which to assign absolute configurations in the synthetically important [‘-(Ar)CCH-CHCH-’]Fe(CO)₃ series.     

Pseudomonas stutzeri 1317合成中长链聚羟基脂肪酸酯的组成分析模型

Pseudomonasstutzeri 1317可以在不同碳源上生长,合成不同共聚单体单元组成的中长链聚羟基脂肪酸酯(mclPHAs).本文在已知的代谢途径的基础上,提出了关于mclPHAs组成的数学模型,结果表明,mclPHAs的共聚单体单元组成主要取决于前体生成途径,以及该途径和聚合途径酶对不同碳原子数前体的选择性.实验结果与文献报道结果均验证了该模型.代谢控制分析的结果表明,碳数为8～10的前体的聚合效率最高.通过调制前体生成途径,可以有效调节PHA的单体单元组成.     

Purification and characterization of a microbial dehydrogenase

Pseudomonas fluorescens (strain BTP9) was found to have at least two NAD(P)-dependent vanillin dehydrogenases: one is induced by vanillin, and the other is constitutive. The constitutive enzyme was purified by ammonium sulfate fractionation, gel-filtration, and Q-Sepharose chromatography. The subunit Mr value was 55,000, determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The native M _r value estimated by gelfiltration chromatography gave a value of 210,000. The enzyme made use of NAD⁺ less effectively than NADP⁺. Benzaldehyde, 4-hydroxybenzaldehyde, hexanal, and acetaldehyde were not oxidized at detectable rates in the presence of NAD⁺ or NADP⁺. The ultraviolet absorption spectrum indicated that there is no cofactor or prosthetic group bound. The vanillin oxidation reaction was essentially irreversible. The pH optimum was 9.5 and the pI of the enzyme was 4.9. Enzyme activity was not affected when assayed in the presence of salts, except FeCl₂. The enzyme was inhibited by the thiol-blocking reagents 4-chloromercuribenzoate and N-ethylmaleimide. NAD⁺ and NADP⁺ protected the enzyme against such a type of inhibition along with vanillin to a lesser extent. The enzyme exhibited esterase activity with 4-nitrophenyl acetate as substrate and was activated by low concentrations of NAD⁺ or NADP⁺. We compared the properties of the enzyme with those of some well-characterized microbial benzaldehyde dehydrogenases.