Evaluation of a sequential extraction for the speciation of thorium in soils from Baotou area, Inner Mongolia

Sequential extraction procedures were widely applied for speciation of radioactive elements. In this study, the sequential extraction procedure developed by Martinez-Aguirre was employed for quantification of different chemical forms of thorium in the soil. The total amount of thorium in contaminated soil was much higher by four-fold than the local background value. The soil properties affect the amount of thoriurn and distribution of fractions in contaminated soil. Results showed that the proportion of thorium in soils from Baotou was found as the residual fraction (F5 + F6) > absorbed fraction (F3), coprecipitated fraction (F4) > carbonates fraction (172) and exchangeable fraction (F1) that could be available to plants. The recovery, calculated by ratio of the sum of the six fractions to the pseudo-total content of thorium, was in the range from 96% to 110%. A comparison was carried out between the sequential extraction and the single extraction to evaluate the selectivity of the extractants. It was found that the amount of thorium of absorbed fraction (H) was higher in the single extraction than that estimated in the sequential extraction, possibly duo to transform of the labile form. While for non-residual fraction analysis, the single extraction scheme was a desirable alternative to the sequential extraction procedure.

Attenuation of Edwardsiella tarda Virulence by Small Peptides That Interfere with LuxS/Autoinducer Type 2 Quorum Sensing

Edwardsiella tarda is a gram-negative pathogen with a broad host range that includes humans, animals, and fish. Recent studies have shown that the LuxS/autoinducer type 2 (AI-2) quorum sensing system is involved in the virulence of E. tarda. In the present study, it was found that the E. tarda LuxS mutants bearing deletions of the catalytic site (C site) and the tyrosine kinase phosphorylation site, respectively, are functionally inactive and that these dysfunctional mutants can interfere with the activity of the wild-type LuxS. Two small peptides, 5411 and 5906, which share sequence identities with the C site of LuxS, were identified. 5411 and 5906 proved to be inhibitors of AI-2 activity and could vitiate the infectivity of the pathogenic E. tarda strain TX1. The inhibitory effect of 5411 and 5906 on AI-2 activity is exerted on LuxS, with which these peptides specifically interact. The expression of 5411 and 5906 in TX1 has multiple effects (altering biofilm production and the expression of certain virulence-associated genes), which are similar to those caused by interruption of luxS expression. Further study found that it is very likely that 5411 and 5906 can be released from the strains expressing them and, should TX1 be in the vicinity, captured by TX1. Based on this observation, a constitutive 5411 producer (Pseudomonas sp. strain FP3/pT5411) was constructed in the form of a fish commensal isolate that expresses 5411 from a plasmid source. The presence of FP3/pT5411 in fish attenuates the virulence of TX1. Finally, it was demonstrated that fish expressing 5411 directly from tissues exhibit enhanced resistance against TX1 infection.

Attenuation of Edwardsiella tarda Virulence by Small Peptides That Interfere with LuxS/Autoinducer Type 2 Quorum Sensing

Edwardsiella tarda is a gram-negative pathogen with a broad host range that includes humans, animals, and fish. Recent studies have shown that the LuxS/autoinducer type 2 (AI-2) quorum sensing system is involved in the virulence of E. tarda. In the present study, it was found that the E. tarda LuxS mutants bearing deletions of the catalytic site (C site) and the tyrosine kinase phosphorylation site, respectively, are functionally inactive and that these dysfunctional mutants can interfere with the activity of the wild-type LuxS. Two small peptides, 5411 and 5906, which share sequence identities with the C site of LuxS, were identified. 5411 and 5906 proved to be inhibitors of AI-2 activity and could vitiate the infectivity of the pathogenic E. tarda strain TX1. The inhibitory effect of 5411 and 5906 on AI-2 activity is exerted on LuxS, with which these peptides specifically interact. The expression of 5411 and 5906 in TX1 has multiple effects (altering biofilm production and the expression of certain virulence-associated genes), which are similar to those caused by interruption of luxS expression. Further study found that it is very likely that 5411 and 5906 can be released from the strains expressing them and, should TX1 be in the vicinity, captured by TX1. Based on this observation, a constitutive 5411 producer (Pseudomonas sp. strain FP3/pT5411) was constructed in the form of a fish commensal isolate that expresses 5411 from a plasmid source. The presence of FP3/pT5411 in fish attenuates the virulence of TX1. Finally, it was demonstrated that fish expressing 5411 directly from tissues exhibit enhanced resistance against TX1 infection.

Screening of genes expressed in vivo after infection by Vibrio anguillarum M3

Aims: Genes uniquely expressed in vivo may contribute to the overall pathogenicity of an organism and are likely to serve as potential targets for the development of new vaccine. This study aims to screen the genes expressed in vivo after Vibrio anguillarum infection by in vivo-induced antigen technology (IVIAT). Methods and Results: The convalescent-phase sera were obtained from turbot (Scophthalmus maximus) survived after infection by the virulent V. anguillarum M3. The pooled sera were thoroughly adsorbed with M3 cells and Escherichia coli BL21 (DE3) cells. A genomic expression library of M3 was constructed and screened for the identification of immunogenic proteins by colony immunoblot analysis with the adsorbed sera. After three rounds of screening, 19 putative in vivo-induced (ivi) genes were obtained. These ivi genes were catalogued into four functional groups: regulator/signalling, metabolism, biological process and hypothetical proteins. Three ivi genes were insertion-mutated, and the growth and 50% lethal dose (LD50) of these mutants were evaluated. Conclusions: The identification of ivi genes in V. anguillarum M3 sheds light on understanding the bacterial pathogenesis and provides novel targets for the development of new vaccines and diagnostic reagents. Significance and Impact of the Study: To the best of our knowledge, this is the first report describing in vivo-expressed genes of V. anguillarum using IVIAT. The screened ivi genes in this study could be new virulent factors and targets for the development of vaccine, which may have implications for the development of diagnostic regents.

Screening of genes expressed in vivo after infection by Vibrio anguillarum M3

Aims: Genes uniquely expressed in vivo may contribute to the overall pathogenicity of an organism and are likely to serve as potential targets for the development of new vaccine. This study aims to screen the genes expressed in vivo after Vibrio anguillarum infection by in vivo-induced antigen technology (IVIAT). Methods and Results: The convalescent-phase sera were obtained from turbot (Scophthalmus maximus) survived after infection by the virulent V. anguillarum M3. The pooled sera were thoroughly adsorbed with M3 cells and Escherichia coli BL21 (DE3) cells. A genomic expression library of M3 was constructed and screened for the identification of immunogenic proteins by colony immunoblot analysis with the adsorbed sera. After three rounds of screening, 19 putative in vivo-induced (ivi) genes were obtained. These ivi genes were catalogued into four functional groups: regulator/signalling, metabolism, biological process and hypothetical proteins. Three ivi genes were insertion-mutated, and the growth and 50% lethal dose (LD50) of these mutants were evaluated. Conclusions: The identification of ivi genes in V. anguillarum M3 sheds light on understanding the bacterial pathogenesis and provides novel targets for the development of new vaccines and diagnostic reagents. Significance and Impact of the Study: To the best of our knowledge, this is the first report describing in vivo-expressed genes of V. anguillarum using IVIAT. The screened ivi genes in this study could be new virulent factors and targets for the development of vaccine, which may have implications for the development of diagnostic regents.

Functional characterization of sll0659 from Synechocystis sp PCC 6803

Synchocystis sp. PCC 6803 lacks a gene for the any known types of lycopene cyclase. Recently, we reported that sll0659 (unknown for its function) from Synechocystis sp. PCC6803 shows similarity in sequence to a lycopene cyclase gene-CruA from Chlorobium tepidum. To test, whether Sll0659 encoded protein serves as lycopene cyclase, in this study, we investigated the carotenoids of the wild types ans mutants, In the sll0659 deleted mutant, there is no blockage at the lycopene cyclization step. Our results demonstrate that sll0659 does not affect lycopene cyclization. However, the ultrastructure of mutants suggests the involvement or necessity of sll0659 in the cell division.

Induction and characterization of green pigmentation mutant in Porphyra yezoensis Ueda

The free living conchocelis of Porphyra yezoensis Ueda was treated with N-methyl-N-nitro-N-nitrosoguanidine to induce pigmentation mutants. The artificial green pigmentation mutant of P. yezoensis conchocelis, which was composed entirely of green cells, was isolated through visualization with the unaided eye. The acquired green conchocelis was further developed into a green gametophytic blade. This mutant was relatively stable in color in both gametophytic blade and conchocelis phases. The gametophytic blade mutant was successively cultivated for commerce at some Porphyra farms in Rudong, China, and few wild type or sectorially variegated gametophytic blade occurred, indicating that the green mutant has commercial value. The green mutant was characterized as having lower phycoerythrin and higher phycocyanin content, and SDS-PAGE suggested that phycoerythrin was missing the gamma-subunit in comparison to the wild type. The wild type and the green mutant showed a clear difference in 02 evolution rates in white, green, yellow, and red light, which might be due to the qualitative and quantitative changes of phycoerythrin, and the quantitative difference of phycocyanin. (C) 2008 Elsevier B.V. All rights reserved.

Construction and characterization of a live, attenuated esrB mutant of Edwardsiella tarda and its potential as a vaccine against the haemorrhagic septicaemia in turbot, Scophthamus maximus (L.)

The esrB gene of Edwardsiella tarda, which encodes a regulator protein of the type III secretion system, was mutated by the unmarked deletion method and reintroduced by allelic exchange into the chromosome of E. tarda LSE40 by means of the suicide vector pRE 112. The LSE40 esrB mutant was highly attenuated when inoculated intraperitoneally into turbot Scophthamus maximus L., showing a 50% lethal dose of 10(8.1) cfu/fish. The esrB mutants were not recoverable from the internal organs at 14 days post-inoculation. Vaccination with a single dose of 10(5)-10(7) cfu/fish of the esrB mutant elicited significant protection against the wildtype strain of E. tarda LSE40 (relative percentage survival > 50%). The protection correlated well with the antibody titres in the serum of vaccinated fish. (c) 2006 Elsevier Ltd. All rights reserved.

贵阳市郊（喀斯特地区）菜园土重金属的生物地球化学循环与绿色作物生产

随着城市化进程的快速推进，大量蔬菜等食物由农村向城市输送，因此促进了城郊结合部蔬菜基地的发展。然而，城市化发展却导致越来越严重的城市和城郊土壤和大气污染，加上现代化生产中化肥和农用化学品的大量使用等，使得重金属在菜园土中大量积累，并可能通过食物链进入人体，威胁人类身体健康。因此，对重金属在土壤－蔬菜体系间迁移的生物地球化学行为的研究是我们了解和防治蔬菜重金属污染、促进绿色作物生产和保护人类健康的关键。 本文选择世界典型喀斯特地区的贵阳市市郊的菜园土－蔬菜体系为主要研究对象，通过系统地对土壤、主要蔬菜和大气沉降物质的元素分析以及铅同位素分析，对研究区域菜园土的主要理化性质、土壤（以及剖面）和蔬菜样品中重金属Cu、Pb、Zn和Cd的含量变化、菜园土以及土壤剖面重金属的形态分布等特征进行了研究。利用微量元素地球化学以及同位素地球化学理论，并结合土壤学研究理论和方法探讨了重金属在菜园土（石灰土和黄壤）和蔬菜体系间的赋存形态、重金属元素的来源、迁移与转化规律及其中的主要控制因素。 主要研究结果认为：贵阳市郊菜园土重金属元素含量变化与土壤母质显著相关，黄壤类型菜园土处于中度污染水平，石灰土类型菜园土处于轻度污染水平。菜园土中重金属形态以残余态为主，其次为有机结合态，再次为铁锰氧化物结合态和酸可提取态。土壤剖面中，菜园土表层大多数重金属含量高于背景剖面，其余各层吻合度较高。土壤剖面中重金属的形态分布仍以残余态为主，菜园土剖面上各元素的生物可利用态即酸可提取态、氧化物结合态和有机结合态则均要高于背景剖面，Pb和Zn主要受到有机结合态的影响，而Cd则三种形态的含量均高于背景剖面，种种迹象表明人为活动增加了菜园土重金属的活性和生物有效性，且以有机结合态的改变最为显著。 蔬菜中红薯可食部位的各项重金属富集系数均大于其他蔬菜，最容易受到土壤中重金属的影响；在土壤－蔬菜体系中，重金属元素含量的分布总体特征为菜园土>根>茎叶>果实，体系内元素的迁移在土壤/蔬菜根界面上最为关键，起着控制作用，此界面上各元素的迁移系数顺序为Cd>>Cu，Zn>Pb，大多数重金属元素在黄壤类型的菜园土中的迁移系数要小于石灰土类型的；在土壤－红薯和土壤－辣椒体系中，Cd的迁移系数随土壤pH的增加而降低，而其余元素的迁移系数则随土壤pH的增加而增加；土壤主成分与土壤理化性质对重金属形态分布有显著影响，但BCR连续提取法得到的土壤中重金属元素的各生物可利用态的含量与蔬菜根部的含量相关性不大；覆膜种植方式使土壤pH由4.5降低到3.8，并改变了其它物化参数，从而影响重金属的形态分布及其在蔬菜体内的含量分布特征，极可能增加农业系统中重金属的环境风险；铅稳定同位素分析表明，土壤中的铅主要来自于母岩的风化，蔬菜中放射成因铅明显略低于菜园土，菜园土和蔬菜中铅同位素组成在208Pb/206Pb对207Pb/206Pb的分布图上呈直线分布（在菜园土－蔬菜体系中，土壤样品、蔬菜不同部位的样品、以及雨水样品的铅同位素组成的分布也形成了极好的直线），显示明显的两端元混合体系；根据各端元物质铅同位素组成计算，土壤铅对蔬菜根部、茎叶的贡献值由71.8%~77.7%降低到16.0%~45.4%之间，大气铅的贡献则沿根向茎叶和果实逐渐增加，研究结果显示大气污染对蔬菜重金属Pb的贡献不可忽视。

黔西南滥木厂铊矿化区河流沉积物重金属环境地球化学及环境效应研究

矿山环境重金属污染及其生态效应研究是环境地球化学研究的热点问题之一，其中水环境生态系统中的沉积物重金属污染由于可能影响流域水环境安全而备受关注。贵州矿产资源丰富，其开采利用过程中的重金属元素污染十分严重，尤其是Tl、As和Hg的污染备受关注。本研究选择黔西南滥木厂铊矿化区为研究对象，通过分析该地区河流沉积物中铊、砷、汞等重金属元素的环境地球化学分布特征，对重金属污染状况进行评价，并探讨其对环境的生态危害，得到以下几点认识： 1. 滥木厂铊矿化区河流沉积物中重金属Tl、Hg、As和Cd的含量相对很高。其中，Tl、Hg和As在矿山影响区河流沉积物中平均含量分别为23.3 mg/kg、46.8 mg/kg 和97.3 mg/kg，比页岩平均含量高几十倍至上百倍，而矿山未影响区及对照区河流沉积物中含量都相对较低。Cd在矿渣以及清水河矿山影响区、矿山未影响区和对照区河流沉积物中的平均含量都相对较高，分别为0.97 mg/kg、1.31 mg/kg、1.17 mg/kg和1.21 mg/kg，约为页岩平均含量的2～5倍，且变化不明显。重金属环境地球化学分析表明，Tl、Hg和As为同源污染物质，主要来自矿山硫化物的风化淋漓；Cd的高含量与矿山联系不明显，可能是由于地域上的Cd异常所致。Cu、Cr、Zn和Pb的含量都相对较低，只略高于页岩平均含量。 2. 地质累积指数（Igeo）和潜在生态危害系数（RI）分析评价结果显示，滥木厂清水河沉积物主要受到Hg、Tl、As以及Cd的污染。受矿山影响的河流沉积物中Hg和Tl的污染很严重，具有很强的潜在生态危害；As和Cd次之；Zn、Cu、Cr和Pb的污染不明显，潜在生态危害很小。 3. 沉积物中重金属各形态分级提取分析（BCR）表明，受矿山影响的滥木厂清水河沉积物及剖面沉积物中：不但总Tl含量很高，有效态Tl含量也高，平均分别为6.0 mg/kg 和5.9 mg/kg，对环境的生态危害很大；Hg虽然总含量非常高，但其酸可提取态含量都低于仪器的检测下限，可还原态含量也不高，平均分别只为0.46 mg/kg 和1.53 mg/kg，主要集中在不易释放的可氧化态和非常稳定的残余态，对环境的生态危害一般；As的总含量较高，但有效态平均含量只为6.51 mg/kg和1.58 mg/kg，对环境的生态危害较小；Cd的总含量也相对较高，有效态平均含量也分别达0.55 mg/kg和0.52 mg/kg，对环境的危害可能较大；Cr、Cu、Zn及Pb的总含量和有效态含量都较低，对环境的生态危害较小。 4. 滥木厂铊矿化区河流沉积物中Tl、Hg和Cd的重金属污染的生态危害性主要表现为Tl、Hg和Cd对食物链的直接或间接污染。Tl和Cd易在农作物中富集，Hg甲基化后也可以在农作物中富集，其人体健康危害性较大。