寡盐水鱼池藻菌土腥异味化合物研究

通过利用固相微萃取-气质联用色谱测定天津市寡盐水养鱼池中浮游藻类和放线菌的次生代谢产物——土腥异味化合物（土臭味素和二甲基异莰醇）浓度,感官评价养殖鱼土腥异味程度,同时测定浮游藻类和放线菌生物量,探讨鱼池中土臭味素和二甲基异莰醇浓度、浮游藻类和放线菌生物量以及养殖鱼异味之间的相互关系。结果表明,寡盐水养鱼池水体中普遍存在土臭味素和二甲基异莰醇,其中二甲基异莰醇是鱼池中的主要异味物质,浓度0．33—5302．70ng·L^-1,土臭味素浓度相对较低,0．29～12．10ng·L^-1。养鱼池中共测到6门94属的浮游藻类,生物量0．07～186．48mg·L^-1,以蓝藻Cyanophyta、裸藻Euglenophyta等种类为主。放线菌共测到3个属,总生物量0．01×10^4-1．50×10^4个·L^-1,以链霉菌属Streptomyces为主。巨颤藻Oscillatoria princeps和放线菌是天津地区寡盐水养鱼池中能够产生二甲基异莰的主要产源。水体异味和鱼肉发生异味不同步。     

南水北调中线干渠异味物质时空动态及其影响因素

为认识南水北调中线干渠异味物质的时空动态,于2018年9月至2019年8月对干渠沿线9个样点开展了6种异味物质、藻类群落及理化因子的逐月同步调查;结果显示:二甲基异莰醇含量平均值为(7.431±9.631)ng/L,夏季略超出嗅阈值;β-环柠檬醛和β-紫罗兰酮平均值分别为(12.371±12.800)和(11.973±...     

盐度对早期链霉菌产生二甲基异莰醇和土臭味素的影响

天津是中国北方重要的渔业生产基地,2006年全市水产养殖面积430 km2,水产品总产量35.5万吨,其中养殖产量30万吨,渔业产值40亿元。天津养鱼池水盐度普遍在2-5,属于寡盐水鱼池,但在该地区采取高密度精养模式生产鱼类普遍存在土腥异味,降低了水产品食用价值和养殖效益。       

天然水体中两种主要异嗅物质的来源及迁移转化研究进展

近年来,水中嗅味问题逐渐引起关注。研究发现,天然水体中异嗅物质主要是微生物和藻类的挥发性次级代谢产物。总结了天然水体中常见的两种异嗅物质土臭素(GSM)和二甲基异莰醇(MIB)的来源及其在生物体内的合成途径。介绍了异嗅物质通过吸附、挥发、光解、生物降解等一系列作用在饮用水水源中的迁移转化以及其进入水体生物的途径。     

人工滩涂湖泊滴水湖浮游藻类群落特征

于2009年3月—2010年2月逐月对中国最大人工滩涂湖泊——滴水湖的浮游藻类群落特征进行研究。利用CANOCO4.5软件对浮游藻类数据和环境因子数据进行典范对应分析(CCA),以揭示浮游藻类对生态环境的响应。结果表明:全年共检测到浮游藻类186种及变种,隶属于8门92属,其中绿藻门种类最多,其次是蓝藻门和硅藻门;主要优势种为小席藻、微小平裂藻、银灰平裂藻、不定微囊藻、弱细颤藻、啮蚀隐藻、四尾栅藻、扁圆卵形藻;藻类的年均丰度和年均生物量分别为(4552.29±4591.33)×104cells·L-1和8.15±6.63mg·L-1,藻类现存量各月份间差异极显著(P<0.01),但站点间差异不显著;多样性分析显示,藻类物种多样性较好;典范对应分析表明,水温、总氮等是影响滴水湖藻类群落结构的主要因素。     

水分对具鞘微鞘藻构建人工藻结皮的作用

为探讨水分在利用室内培养具鞘微鞘藻构建人工藻结皮中的作用,本文研究了不同施水量和施水时间下人工藻结皮中的藻类生物量、结皮厚度、抗压强度和微结构变化.结果表明:利用具鞘微鞘藻在裸沙上接种,无水处理藻类生物量极低,无藻结皮形成.随着施水量的增加,藻结皮开始出现直至形成稳定的藻结皮,藻类生物量、结皮厚度和抗压强度显著增加,藻丝和胞外多糖逐渐增多,与沙粒缠绕成复杂的网状结构.施水15 d,形成稳定的藻结皮,藻类生物量、结皮厚度和抗压强度最高.具鞘微鞘藻形成藻结皮的最适施水量是3～4L·m-2·d-1,施水时间为15 d.土壤可利用水分可促进具鞘微鞘藻的代谢活动和胞外多糖合成,从而增加藻类生物量,提高其耐旱能力,早期的水分获得是其成功形成藻结皮的关键因素.研究结果将为利用荒漠藻类进行人工生物结皮恢复提供重要的理论依据.     

微囊藻对柔细束丝藻生长及土臭素合成与释放的影响

文章选择两种特征不同的微囊藻——产毒的铜绿微囊藻(Microcystis aeruginosa)和无毒的惠氏微囊藻(Microcystis wesenbergii),分别以不同的接种比例(1﹕2、1﹕1和2﹕1)与产土臭素(Geosmin)的柔细束丝藻(Aphanizomenon gracile)混合培养,以探索种间相互作用对藻类生长和束丝藻土臭素合成与释放的影响。结果表明,在共培养条件下,两种微囊藻均抑制了柔细束丝藻的生长,而柔细束丝藻却促进了两种微囊藻的生长。惠氏微囊藻促进了柔细束丝藻土臭素的释放(接种比例为1﹕1时,束丝藻胞外土臭素的细胞份额达到269.43 fg/cell),仅在生长早期与生长受到抑制阶段促进了土臭素的合成;铜绿微囊藻在共培养早期促进了束丝藻土臭素的合成,但共培养却抑制了土臭素的释放,而且在共培养的中后期已检测不到土臭素。研究结果表明,在自然水体中束丝藻与微囊藻的季节演替过程中,微囊藻在与束丝藻的竞争中处于优势,且微囊藻对束丝藻的竞争压力促使后者合成异味物质,随着束丝藻的消亡可能伴随大量异味物质的释放,增加异味事件发生风险。     

沉水植物化感作用控藻能力评述

沉水植物所释放的化学物质对藻类的抑制作用是浅水湖泊维持清水状态的机制之一.本文从具有化感活性的沉水植物在湖泊中出现的频度、盖度、化感物质的种类、抑藻效应等方面对化感控藻进行了评述.已有研究结果表明：穗花狐尾藻、金鱼藻、伊乐藻等是具有很高活性的沉水植物,尤其是在其生物量达到一定程度,且湖泊中的优势藻为较敏感的种类时,沉水植物分泌的化感物质对浮游藻类的抑制作用更强;沉水植物释放的多酚类等化感物质具有控藻能力;化感物质对于不同种类藻的抑制作用具有选择性,蓝藻和硅藻比绿藻更为敏感,附生藻类通常比浮游藻类具有更高的耐受性;环境因素如光照、营养限制、温度等会显著影响沉水植物化感作用效果.沉水植物的化感控藻研究尚处于初始阶段,关于环境因素对化感作用的影响、化感物质的分离鉴定、选择性抑藻机理以及化感物质代谢途径等方面还有待深入、全面的研究.     

上海公园水体夏季浮游植物群落与环境因子的关系

为了解公园水体浮游植物群落状况,分析浮游植物物种分布和环境因子之间的关系,揭示浮游植物物种对生态环境的需求,于2008年7月和9月对上海市11个公园水体浮游植物群落进行了调查,对获得的浮游植物数据和环境因子数据进行典范相关分析(CCA),并绘制了物种与环境因子关系的二维排序图。结果表明：调查期间共鉴定出浮游植物384种,隶属于8门,浮游植物密度范围为2.01×10⁵～57.60×10⁵ cells·L^-1;群落组成以蓝藻、裸藻、硅藻和绿藻为主,主要优势种有细微颤藻、无常蓝纤维藻、尾裸藻、颗粒直链藻、梅尼小环藻、普通小球藻、四尾栅藻等;7月影响浮游植物分布的主要环境因子依次为铵态氮、溶解氧、水温和总磷,而9月的pH值、水温、溶解氧、透明度和总氮含量对浮游植物的分布产生影响较大;其中,透明度和浮游动物量是影响隐藻、甲藻和硅藻藻类生物量的主要环境因子,而蓝藻、裸藻、绿藻主要受水体氮磷营养盐浓度和溶解氧的影响。     

南美白对虾精养塘浮游微藻动态研究

2006年4月30日～2006年8月31日,对舟山市马岙镇的旭旺无公害对虾精养基地水体的浮游微藻群落结构进行调查分析.结果表明:精养塘中共检出常见浮游微藻5门16种,其中蓝藻4种,绿藻5种,硅藻5种,裸藻1种,甲藻1种.主要蓝藻有微小平裂藻(Merismopedia tenuissima.)、小席藻(Phorimidium sp.)、螺旋藻(Spirulina sp.)等;常见绿藻有小球藻(Chlorella sp.)、衣藻(Chlamydomonas sp.)等;常见硅藻有舟形藻(Navicula sp.)、尖针杆藻(Synedra acus)等.养殖早期3门9种,蓝藻门与裸藻门的微藻未检查到,且浮游微藻细胞数量为0.8×10⁷cells·L^-1,香浓多样性指数平均为0.445.养殖后期4门12种,多甲藻未出现了,浮游微藻细胞数量为1.5×10⁷ cells·L^-1,香浓多样性指数平均为0.375.浮游藻类多样性指数总体表现为养殖前期高后期低的特征.     

壳聚糖酶的克隆表达与壳寡糖的制备分析

目的:克隆壳聚糖酶基因于大肠杆菌中实现高表达,制备壳寡糖。方法:以枯草芽孢杆菌总DNA为模板扩增壳聚糖酶基因(CSN),克隆至载体pET23a(+)上,转化菌株BL21(DE3)。重组子经0.5 mmol/L IPTG诱导后,SDS-PAGE和质谱检测与鉴定重组酶。酶纯化后水解壳聚糖,薄层色谱分析其水解产物。结果:质谱证明壳聚糖酶(31.5kDa)成功表达,表达量占菌体总蛋白的45%左右。纯化后重组酶浓度为900 mg/L,纯度95%、回收率85%,酶活力为10 000 U/mg。壳聚糖降解产物为壳二糖至壳四糖。结论:原核表达载体pET23a(+)-CSN构建正确,壳聚糖酶表达量与活性高,适用于水解壳聚糖制备壳寡糖。     

国内外蝗害治理技术现状与展望

本文首先概述了国内外蝗虫发生与为害的态势,总结了现阶段我国蝗虫发生与为害的主要特点:即农田飞蝗暴发频繁而且严重,草原土蝗的发生时常造成严重的经济损失,而且侵入城市干扰市民生活,我国与周边国家之间蝗虫过境迁移频繁,使用化学农药污染环境和农产品;分析了国内外蝗虫防治对策与技术的发展现状,重点介绍了应急防治和可持续治理对策、...     

放牧对牧草光合作用、呼吸作用和氮、碳吸收与转运的影响

研究放牧对草地植物生理活动的影响,对于揭示草地放牧演替的生理机制有重要意义.大量研究表明,家畜放牧对牧草光合作用、呼吸作用以及C和N吸收与转运的影响,可以分为生理伤害和生理恢复2个阶段.放牧通过改变草地冠层结构影响牧草光合作用,净光合作用速率短期内迅速下降,随着叶面积指数增加又逐渐上升,呼吸作用有相似的变化趋势.牧草放牧后再生长所需的C和N最初主要来自根系和留茬中的贮藏物质,此后随着牧草生长恢复逐渐由同化作用供给,C代谢与土壤N水平负相关.放牧后牧草生理活动变化与牧草遗传特性、种间竞争、家畜放牧特征、非生物环境等因素密切相关.     

Kinetics and thermodynamics of peroxidase- and laccase-catalyzed oxidation of N-substituted phenothiazines and phenoxazines

N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k _cat/K _m) varied from 1 ×10⁷M⁻¹s⁻¹to 2.6×10⁸M⁻¹s⁻¹ at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable groups with pK _a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent bimolecular rate constants varied from 1.8×10⁵M⁻¹s⁻¹ to 2.0×10⁷M⁻¹s⁻¹ at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO, fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×10⁸M⁻¹s⁻¹ and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×10⁷M⁻¹s⁻¹ and 0.29 eV. Received: 20 September 1999 / Accepted: 24 February 2000     

Coiled-coil nanomechanics and uncoiling and unfolding of the superhelix and alpha-helices of myosin

The nanomechanical properties of the coiled-coils of myosin are fundamentally important in understanding muscle assembly and contraction. Force spectra of single molecules of double-headed myosin, single-headed myosin, and coiled-coil tail fragments were acquired with an atomic force microscope and displayed characteristic triphasic force-distance responses to stretch: a rise phase (R) and a plateau phase (P) and an exponential phase (E). The R and P phases arise mainly from the stretching of the coiled-coils, with the hinge region being the main contributor to the rise phase at low force. Only the E phase was analyzable by the worm-like chain model of polymer elasticity. Restrained molecular mechanics simulations on an existing x-ray structure of scallop S2 yielded force spectra with either two or three phases, depending on the mode of stretch. It revealed that coiled-coil chains separate completely near the end of the P phase and the stretching of the unfolded chains gives rise to the E phase. Extensive conformational searching yielded a P phase force near 40 pN that agreed well with the experimental value. We suggest that the flexible and elastic S2 region, particularly the hinge region, may undergo force-induced unfolding and extend reversibly during actomyosin powerstroke.     

白术同源四倍体的诱导和鉴定及其与二倍体过氧化物酶的比较

以白术（Atractylodes macrooephala Koidz.）二倍体组培苗为材料,对其四倍体诱导方法进行研究,共获得45个白术同源四倍体株系,为优良株系的选育提供了材料。此外,还分析比较了其中8个白术四倍体株系与二倍体的过氧化物酶同工酶（POD）的酶谱差异,发现四倍体各株系过氧化物酶同工酶谱比二倍体的均多了Rf0.310的谱带,且总过氧化物酶比活力也发生了很大改变,对探讨白术四倍体优良株系的生理生化机理具有一定的参考价值。     

Synthesis of hapten and conjugates of coumestrol and development of immunoassay

3-O-Carboxymethylcoumestrol was prepared as the hapten for immunoassay by a partial alkylation of coumestrol with ethyl chloroacetate in acetone alkalized with potassium carbonate. 3-O-Ethoxycarbonylmethylcoumestrol was separated by column chromatography and finally was hydrolyzed with formic acid. 1H and 13C NMR data (APT, COSY, HMQC, and HMBC) revealed that the reaction was regioselective, as 3-O-ethoxycarboxymethylcoumestrol was the only monosubstituted derivative. The hapten was then conjugated to bovine serum albumin and used for immunization of rabbits. A radioimmunoassay (RIA) system was established based on the polyclonal antiserum and a 125I-labeled hapten-tyrosine methyl ester conjugate as the radioligand. Parameters of the RIA: sensitivity: 12 pg per tube, 50% intercept: 140 pg per tube, working range: 20-4000 pg per tube. The cross-reactivity of a panel isoflavonoid and lignan phytoestrogens was either negligible (e.g. formononetin 0.07%; biochanin A 0.06%) or not detectable at all. The major immunoreactive peak in HPLC fractions from an alfalfa extract had the same retention time as coumestrol standard and represented 94.8% of the signal. The remaining 5.2% of immunoreactivity was distributed between five minor peaks. We conclude that after the validation for particular matrices, the method will be a useful tool for analysis of coumestrol, especially in low volume and low concentration samples.     

Morphology and putative function of the colon and cloaca of marine and freshwater snakes

Among tetrapods, evidence for postrenal modification of the urine by the distal digestive tract (including the colon and cloaca) is highly variable. Birds and bladderless reptiles are of interest because the colon and cloaca represent the only sites from which water and ions can be reclaimed from the urine secreted by the kidney. For animals occupying desiccating environments (e.g., deserts and marine environments), postrenal modification of the urine may directly contribute to the maintenance of hypo‐osmotic body fluids. We compared the morphology and distribution of key proteins in the colon, cloaca, and urogenital ducts of watersnakes from marine (Nerodia clarkii clarkii) and freshwater (Nerodia fasciata) habitats. Specifically, we examined the epithelia of each tissue for evidence of mucus production by examining the distribution of mucopolysaccharides, and for evidence of water/ion regulation by examining the distribution of Na⁺/K⁺‐ATPase (NKA), Na⁺/K⁺/Cl^? cotransporter (NKCC), and aquaporin 3 (AQP3). NKCC localized to the basolateral epithelium of the colon, urodeal sphincter, and proctodeum, consistent with a role in secretion of Na⁺, Cl^?, and K⁺ from the tissue, but NKA was not detected in the colon or any compartment of the cloaca. Interestingly, NKA was detected in the basolateral epithelium of the ureters, suggesting the urothelium may play a role in active ion transport. AQP3 was detected in the ureters and coprodeal complex, consistent with a role in urinary and fecal dehydration or, potentially, in the production of the watery component of the mucus secreted by the coprodeal complex. Since no differences in general cloacal morphology, production of mucus, or the distribution of ion transporters/water channels were detected between the two species, cloacal osmoregulation may either be regulated by proteins not examined in this study or may not be responsible for the differential success of N. c. clarkii and N. fasciata in marine habitats. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.