Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability

An emerging paradigm in soil science suggests microbes can perform ‘N mining’ from recalcitrant soil organic matter (SOM) in conditions of low N availability. However, this requires the production of extracellular structures rich in N (including enzymes and structural components) and thus defies stoichiometric expectation. We set out to extract newly synthesised peptides from the extracellular matrix in soil and compare the amino acid (AA) profiles, N incorporation and AA dynamics in response to labile inputs of contrasting C/N ratio. Glycerol was added both with and without an inorganic source of N (10% ¹⁵N labelled NH₄NO₃) to a soil already containing a large pool of refractory SOM and incubated for 10 days. The resulting total soil peptide (TSP) and extracellular pools were compared using colorimetric methods, gas chromatography, and isotope ratio mass spectrometry. N isotope compositions showed that the extracellular polymeric substance (EPS) contained a greater proportion of products formed de novo than did TSP, with hydrophobic EPS-AAs (leucine, isoleucine, phenylalanine, hydroxyproline and tyrosine) deriving substantially more N from the inorganic source provided. Quantitative comparison between extracts showed that the EPS contained greater relative proportions of alanine, glycine, proline, phenylalanine and tyrosine. The greatest increases in EPS-peptide and EPS-polysaccharide concentrations occurred at the highest C/N ratios. All EPS-AAs responded similarly to treatment whereas the responses of TSP were more complex. The results suggest that extracellular investment of N (as EPS peptides) is a microbial survival mechanism in conditions of low N/high C which, from an evolutionary perspective, must ultimately lead to the tendency for increased N returns to the microbial biomass. A conceptual model is proposed that describes the dynamics of the extracellular matrix in response to the C/N ratio of labile inputs.     

Influence of Polypropylene Fiber on the Performance of Thermal Insulating Mortar Made from Expanded Polystyrene Particles

The influences of the types, dosage and length of fibers on EPS thermal insulating mortar were studied. The results show that the addition of fibers have obvious reinforcing effects on EPS thermal insulating mortar. With the addition of polypropylene fib     

新疆奎屯排碱渠生物膜胞外聚合物与As(Ⅲ)的络合作用

新疆奎屯地区是地质背景高砷区,排碱渠水体砷（As）污染严重,排碱渠中普遍发育的生物膜胞外聚合物（EPS）与As之间的络合会影响砷的迁移扩散,进而影响到砷的生物毒性和生态风险。目前,排碱渠中普遍发育的生物膜EPS对水中As的迁移转化及行为归宿的影响还完全不清楚。本文结合荧光猝灭滴定技术和等温微量热滴定技术研究了该地区普遍发育的藻生物膜EPS与As（Ⅲ）之间的相互作用。荧光猝灭实验表明：排碱渠生物膜EPS有3个荧光峰：峰A属于含芳环基团的蛋白质Ⅱ;峰B属于溶解性的微生物类蛋白质;峰C属于类腐殖酸。峰A和峰B统称为类蛋白质物质,其中峰B被确定为类色氨酸物质。类蛋白物质与As（Ⅲ）具有较强的结合作用,而类腐殖酸物质与As（Ⅲ）几乎没有结合能力。EPS与As（Ⅲ）荧光淬灭作用属于静态淬灭和动态碰撞淬灭,同时存在的复合淬灭机制。EPS中含芳环基团的蛋白质Ⅱ和类色氨酸物质与As（Ⅲ）的结合常数lg Kb分别为3.82和2.22,说明As（Ⅲ）与前者的结合强度比后者大一个数量级,前者与As（Ⅲ）形成络合物的稳定性稍微大于后者。As（Ⅲ）可以与含芳环基团的蛋白质Ⅱ的多类位点结合,且在多类结合位点之间存在拮抗竞争作用,而类色氨酸物质中只有一类位点参与As的络合。等温微量热滴定实验结果经过Independent模型拟合,求得了EPS和As（Ⅲ）络合反应的热动力学参数：ΔH、ΔG、ΔS。负的焓变ΔH和负的吉布斯自由能ΔG证明EPS与As（Ⅲ）间的络合反应是一个自发进行的放热反应。随着络合反应进行,反应体系的无序度增加,反应为熵驱动。排碱渠生物膜EPS中的类蛋白质在As（Ⅲ）的迁移转化及其生态风险中起着重要作用,而EPS中的类腐殖酸物质不会对As（Ⅲ）的环境行为产生显著影响。     

Effects of Heterotrophic and Autotrophic Bacteria on the Stability of Aerobic Granular Sludge

The characteristics of granules of heterotrophic and autotrophic bacteria were studied. The autotrophic granules were characterized by smaller granule size, higher density, higher concentration of extracellular polymeric substances (EPS) and weaker strength compared with the heterotrophic ones. The diameter and density of autotrophic granules were changed in the same fashion, resulting in stable granules, and the heterotrophic granule, however, grew up with the increase of diameter and the decrease of density. According to the strength analysis, it is proposed that in the autotrophic system, the balance between EPS and porosity is the main reason for the long term stability. However, the balance could not be obtained in the heterotrophic system and that the operational conditions could not control the overgrowth of filamentous bacteria was the reason for the instability.     

一种通过肠膜明串珠菌发酵的花样奶布丁的研制

目前市售布丁主要是调制型奶布丁,是根据口味差异调制所需配料,加入明胶等凝固而成,虽有一些"半发酵型"的布丁产品,主要是以酸奶为原料进行调制而成,但其凝固成型过程主要依赖于添加的各种稳定剂,无法兼顾到美味、营养和健康.为此,本文研究了一种以脱脂乳和番茄汁为介质、基于肠膜明串珠菌发酵的花样奶布丁,其保留了牛乳中的各种营养物...     

3种无机盐对念珠藻生长和胞外多糖分泌的影响

为更好地开发和利用地木耳,探讨了不同浓度的NaCl、NaNO3、Ca(NO3)2对地木耳生物量积累和胞外多糖产生的影响。结果表明:NaCl和NaNO3诱导子在低浓度时起促进作用,高浓度时抑制地木耳的生长和胞外多糖的产生,均以20 mmol/L浓度为最佳的诱导条件;而Ca(NO3)2随浓度的增加生物量和多糖含量上升,80 mmol/L诱导作用效果最好。     

日光温室前沿苯板外护增地温效果研究

日光温室前沿设置苯板外护与未设置苯板外护相比,前沿基础苯板外护可以有效地阻止热量横向传导,起到保温隔热作用,哈尔滨地区建造温室基础苯板外护深度应以1 100 mm为建筑参考。     

木材树种对刨花/EPS泡沫复合轻质刨花板性能的影响

为实现刨花板轻量化,通过向芯层引入聚苯乙烯(EPS)泡沫颗粒,制备平均密度为500 kg/m^3的刨花板,探索表芯层刨花构成对板材的剖面密度分布和物理力学性能的影响。结果表明:以杨木细刨花为表层、桉木粗刨花和EPS泡沫颗粒混合物为芯层制备的复合轻质刨花板,其表芯层密度差异最为显著,力学性能达到GB/T 4897-2015《刨花板》中干燥状态下使用的家具型(P2型)刨花板的要求。     

Bacterial induction of the accumulation of phaseollin,pisatin and rishitin and their antibacterial activity

Bean hypocotyls, pea pods and tomato fruits were tested for phaseollin, pisatin and rishitin production when challenged with the phytopathogenic bacteriaErwinia carotovora, Pseudomonas phaseolicola, P. pisi andP. solanacearum, and their isolated extracellular polysaccharides. All bacteria induced phytoalexin accumulation, whereas only phaseollin and pisatin, but not rishitin, were elicited by EPS. The inhibitory effect of these three phytoalexins on bacterial growth was studied in liquid medium; whereas phaseollin and pisatin strongly inhibited growth, only a slight inhibitory effect resulted from the presence of rishitin in the medium.Samenvatting Bonehypocotylen, erwtepeulen en tomatevruchten werden onderzocht op hun vermogen tot vorming van respectievelijk faseolline, pisatine en rishitine, na inoculatie met de fytopathogene bacteriënErwinia carotovora, Pseudomonas phaseolicola, P. pisi enP. solanacearum en na behandeling met oplossingen van hun extracellulaire polysacchariden (EPS). Alle bacteriesoorten induceerden fytoalexinevorming, terwijl hun EPS wel faseolline- en pisatine-, maar geen rishitinevorming induceerden. Faseolline en pisatine remden de groei van de bacteriën in vloeibaar medium sterk; rishitine daarentegen had slechts een geringe groeiremming tengevolge.     

EPS系统助力电机的匹配研究

分析EPS系统助力电机的选型、安装以及电机最大转矩和最大转速的确定,并仿真分析了电机转动惯量和阻尼对转向灵敏度及转向路感的影响,得出的结论可为EPS系统助力电机的匹配设计提供参考。