Polychlorinated Biphenyl (PCB)-Degrading Bacteria Associated with Trees in a PCB-Contaminated Site

The abundance, identities, and degradation abilities of indigenous polychlorinated biphenyl (PCB)-degrading bacteria associated with five species of mature trees growing naturally in a contaminated site were investigated to identify plants that enhance the microbial PCB degradation potential in soil. Culturable PCB degraders were associated with every plant species examined in both the rhizosphere and root zone, which was defined as the bulk soil in which the plant was rooted. Significantly higher numbers of PCB degraders (2.7- to 56.7-fold-higher means) were detected in the root zones of Austrian pine (Pinus nigra) and goat willow (Salix caprea) than in the root zones of other plants or non-root-containing soil in certain seasons and at certain soil depths. The majority of culturable PCB degraders throughout the site and the majority of culturable PCB degraders associated with plants were identified as members of the genus Rhodococcus by 16S rRNA gene sequence analysis. Other taxa of PCB-degrading bacteria included members of the genera Luteibacter and Williamsia, which have not previously been shown to include PCB degraders. PCB degradation assays revealed that some isolates from the site have broad congener specificities; these isolates included one Rhodococcus strain that exhibited degradation abilities similar to those of Burkholderia xenovorans LB400. Isolates with broad congener specificity were widespread at the site, including in the biostimulated root zone of willow. The apparent association of certain plant species with increased abundance of indigenous PCB degraders, including organisms with outstanding degradation abilities, throughout the root zone supports the notion that biostimulation through rhizoremediation is a promising strategy for enhancing PCB degradation in situ.     

西藏青稞根际细菌群落结构及多样性

【目的】分析西藏不同种植区青稞根际土壤细菌群落结构及其影响因素，揭示特定环境下根际细菌生物标志物，为发掘研究优异根际促生菌及其作用提供参考。【方法】采用16S rRNA基因高通量测序技术和数据统计分析，比较了西藏5个市青稞种植区根际土壤细菌群落组成和结构差异，分析了青稞根际细菌生物标志物及群落结构变化的驱动因素。【结果】通过测序45个根际土壤样品获得10 715个操作分类单元（operational taxonomic units，OTUs），共43门、1 244属、2 783种，其中放线菌门（Actinobacteriota）、变形菌门（Proteobacteria）、绿弯菌门（Chloroflexi）、酸杆菌门（Acidobacteriota）、拟杆菌门（Bacteroidota）、厚壁菌门（Firmicutes）、芽单胞菌门（Gemmatimonadota）、粘球菌门（Myxococcota）和髌骨细菌门（Patescibacteria）为优势菌门，相对丰度占比94.92%-96.56%。五个市的根际细菌群落结构存在明显的差异，组间差异大于组内差异（R=0.226 9，P=0.001），其中放线菌门、绿弯菌门、酸杆菌门、拟杆菌门和髌骨细菌门丰度存在显著性差异（P<0.05）。五个市青稞根际土壤存在潜在生物标志物，拉萨和山南只有3个和6个特有细菌进化支，共现网络更为复杂、OTUs间联系更为紧密。变形菌门、绿弯菌门、放线菌门和酸杆菌门是青稞根际土壤中主要的关键细菌门，内生菌门、Methylomirabilota和蓝细菌分别是林芝市、日喀则市和山南市的特有关键类群。青稞根际细菌群落结构的变化主要与环境因子pH、全钾（total potassium，TK）、速效钾（available potassium，AK）、碳磷比（C：P）和海拔有关，其中TK是影响根际土壤细菌群落最重要的因子（r²=0.621 4，P=0.001）。【结论】西藏青稞根际细菌多样性丰富，5市间存在显著差异，且不同生长区青稞根际具有特有的生物标志物，为进一步研究特有根际细菌在青稞生长和环境适应中的作用，发掘优异根际促生菌提供参考。     

小花老鼠簕可培养细菌多样性及其生物学活性研究

小花老鼠簕(Acanthus ebracteatus)是一种生长在红树生态系统的珍稀真红树植物,具有较高的药用价值。为研究小花老鼠簕内生及根际可培养细菌多样性,挖掘其潜在新物种及具有特殊生物学活性的菌株,该文利用7种不同培养基,通过传统稀释涂布法对小花老鼠簕各植物组织及根际土壤可培养细菌进行分离,基于16S rRNA基因序列解析其内生及根际细菌群落结构和多样性特征,应用植物病原菌平板对峙实验和平铺捕食活性测试分析其可培养细菌的抗菌活性。结果表明：(1)基于16S rRNA基因序列分析,发现从小花老鼠簕的根、茎、叶、花及根际土壤中分离得到144株可培养细菌,这些细菌隶属于18目26科37属66种,芽孢杆菌属(Bacillus)和链霉菌属(Streptomyces)为优势菌属,分别占细菌种数的15.1%和13.6%;(2)拮抗多种植物病原菌试验结果显示,获得29株具有拮抗植物病原菌活性的细菌,10株具有广谱抑菌活性,其中链霉菌属菌株拮抗作用最强且菌株Y129为潜在新物种。(3)捕食活性测试结果显示,有5株细菌对金黄色葡萄球菌(Staphylococcus aureus)、耐甲氧西林金黄色葡...     

药用植物刺山柑不同部位细菌群落结构及其多样性

【目的】研究传统药用植物刺山柑（Capparis spinosa L.）不同部位细菌群落结构、物种组成和多样性特征,为药用植物微生物资源的开发及微生物与宿主互作提供理论依据。【方法】本研究以刺山柑地上部植物组织（果实、茎）和地下部土壤（根际土壤、非根际土壤）为研究材料,采用高通量测序技术分析刺山柑不同部位细菌的16S rRNA基因多样性,比较其细菌群落结构和物种组成特征。【结果】刺山柑4种样本共获得的3 649个操作分类单元（operational taxonomic unit,OTU）,属于34门、88纲、248目、464科和1 051属。土壤样本的细菌多样性大于植物组织,细菌群落多样性以根际土壤、非根际土壤、茎和果实的顺序逐渐降低,果实内生细菌群落多样性始终最低,显著低于根际土壤。不同部位相对丰度较高的细菌门如下：植物组织中以变形菌门为主,根际土壤中为变形菌门和放线菌门,非根际土中为厚壁菌门和放线菌门。无色杆菌属（Achromobacter）、欧文氏菌属（Erwinia）、肠球菌属（Enterococcus）、微小杆菌属（Exiguobacterium）、乳杆菌属（Lactobacillus）和克雷伯氏菌属（Klebsiella）主要存在于刺山柑植物组织中。游动球菌属（Planomicrobium）、库克菌属（Kocuria）、类芽孢杆菌属（Paenibacillus）、链霉菌属（Streptomyces）、微枝形杆菌属（Microvirga）和节杆菌属（Arthrobacter）主要分布于土壤中。β多样性分析结果表明,刺山柑植物组织和土壤的细菌群落结构具有显著差异,同类型样本的细菌群落结构相似。【结论】刺山柑土壤样本中细菌群落的多样性和丰富度均高于植物组织,刺山柑不同部位的细菌群落组成不同。本研究对刺山柑不同部位细菌群落结构进行了初步分析,鉴定了各部位细菌群落中的核心菌群,为以后挖掘刺山柑的功能研究和利用提供了准确的微生物信息。     

洮河上游不同海拔紫果云杉根际与非根际土壤细菌多样性及影响因子

【背景】紫果云杉天然林在维护洮河上游生态环境安全方面发挥着重要作用,不同海拔梯度如何影响紫果云杉根际与非根际细菌多样性、土壤养分因子及三者之间的相关性尚不清楚。【目的】深入探索紫果云杉根际与非根际土壤细菌群落结构组成及受控因子。【方法】采用Illumina Miseq平台对洮河上游不同海拔紫果云杉天然林根际与非根际土壤细菌进行测序分析,分析土壤理化因子与细菌多样性随海拔的变化趋势,并通过相关性与冗余分析探究环境因子对细菌群落的影响。【结果】土壤养分因子随海拔升高呈先增加后降低趋势;根际土养分因子组间差异显著(P<0.05),非根际组间差异不显著(P>0.05)。随海拔升高根际微生物物种多样性指数(H)、均匀度指数(E)、丰富度指数(Chao1/ACE)和OTU数目呈单峰型变化趋势;非根际多样性指数随海拔升高呈双峰型变化趋势。土壤细菌多样性与养分因子密切相关,其中有机质、全氮和碱解氮呈显著正相关(P<0.05),而土壤pH和有效磷与细菌多样性呈负相关但不显著(P>0.05)。不同海拔梯度下紫果云杉天然林细菌群落结构一致性较高,从30个样本中获得7 159个细菌OTU,注释到37个门;细菌优势类群为放线菌门、变形菌门、酸杆菌门和绿弯菌门。不同细菌门对土壤养分因子的响应各不相同,有机质、全氮和碱解氮与变形菌门呈显著正相关(P<0.05)。【结论】土壤理化因子能够显著影响紫果云杉根际与非根际细菌多样性和组成,海拔和水热条件等环境因子对植物和土壤的驱动影响是细菌群落结构稳定组成的重要原因。本研究有助于深入理解紫果云杉天然林土壤细菌多样性的变化和驱动机制,为洮河上游天然林恢复与生态恢复提供借鉴。     

Degradation of PCB congeners by bacterial strains

Biological in situ methods are options for the remediation of contaminated sites. An approach to quantify biodegradation by soil bacteria was developed, combining experiment with mathematical modelling. We performed in vitro assays to investigate the potential and kinetics of the wild-type degrader, Burkholderia sp. strain LB400 (expressing bph) and the genetically modified Pseudomonas fluorescens strains F113pcb and F113L::1180 (expressing bph under different promoters) to metabolise individual congeners of polychlorinated biphenyls (PCBs). Kinetics of metabolism was analysed using the Monod model. Results revealed similar patterns of degradable PCB congeners for LB400 and F113L::1180. The degree of PCB degradation was comparable for LB400 and F113L::1180 but was much lower for F113rifpcb. In additional mesocosm experiments with PCB-contaminated soil, the F113 derivatives demonstrated a good survival ability in willow (Salix sp.) rhizosphere. Strain F113L::1180 in combination with willow plants is expected to degrade a large spectrum of PCB congeners in soil. The data from the experiments were used to calculate the time scale of the degradation process in a PCB-contaminated soil. The uncertainty of the model predictions due to the uncertainties of experimental removal velocities and bacterial cell density in soil was quantified.     

Culturable bacteria from Zn‐ and Cd‐accumulating Salix caprea with differential effects on plant growth and heavy metal availability

Aims: To characterize bacteria associated with Zn/Cd‐accumulating Salix caprea regarding their potential to support heavy metal phytoextraction. Methods and Results: Three different media allowed the isolation of 44 rhizosphere strains and 44 endophytes, resistant to Zn/Cd and mostly affiliated with Proteobacteria, Actinobacteria and Bacteroidetes/Chlorobi. 1‐Aminocyclopropane‐1‐carboxylic acid deaminase (ACCD), indole acetic acid and siderophore production were detected in 41, 23 and 50% of the rhizosphere isolates and in 9, 55 and 2% of the endophytes, respectively. Fifteen rhizosphere bacteria and five endophytes were further tested for the production of metal‐mobilizing metabolites by extracting contaminated soil with filtrates from liquid cultures. Four Actinobacteria mobilized Zn and/or Cd. The other strains immobilized Cd or both metals. An ACCD‐ and siderophore‐producing, Zn/Cd‐immobilizing rhizosphere isolate (Burkholderia sp.) and a Zn/Cd‐mobilizing Actinobacterium endophyte were inoculated onto S. caprea. The rhizosphere isolate reduced metal uptake in roots, whereas the endophyte enhanced metal accumulation in leaves. Plant growth was not promoted. Conclusions: Metal mobilization experiments predicted bacterial effects on S. caprea more reliably than standard tests for plant growth‐promoting activities. Significance and Impact of the Study: Bacteria, particularly Actinobacteria, associated with heavy metal‐accumulating Salix have the potential to increase metal uptake, which can be predicted by mobilization experiments and may be applicable in phytoremediation.     

Biodiversity of diazotrophic bacteria within the soil, root and stem of field-grown maize

Recent studies suggest a high diversity of diazotrophic bacteria in maize. However, none of these works have been based on a sufficient number of samples to provide reasonable quantitative estimates of diazotrophic bacterial diversity. Here we present the use of molecular tools and statistical inference to assess diazotrophic bacterial diversity within rhizosphere soils, roots and stems of field grown maize. DNA was isolated from the latter collected from six maize growing regions within the southern most state in Brazil, Rio Grande do Sul. Using conserved primers, nifH Cluster I gene fragments were amplified from each of the three zones, and the products cloned and sequenced. The majority of the sequences were classified within the Proteobacteria with the α-proteobacteria and β-proteobacteria being the most abundant in the rhizosphere soil and stem samples. The γ-proteobacteria were most abundant in rhizosphere soils, less so in roots, and least in the stem samples. According to three different diversity measures, the rhizosphere soil samples possessed greater diazotrophic bacterial diversity than the roots and stems of the maize plants. Only two genera, Azospirillum and Azotobacter, were found in virtually all samples at an abundance of over 1% of the total nifH sequences obtained. Other genera were largely restricted to soil (Methylocystis, Beijerinckia, Geobacter, Rhodovulum, Methylobacterium, Gluconacetobacter, Methylocella, and Delftia), roots (Dechloromonas), or stems (Methylosinus, Raoultella, and Rhizobium). Three genera, Herbaspirillum, Ideonella, and Klebsiella, appeared to dominate in the interior of the plant but were much rarer in soil.     

Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows

A variety of plants growing on metalliferous soils accumulate metals in their harvestable parts and have the potential to be used for phytoremediation of heavy metal polluted land. There is increasing evidence that rhizosphere bacteria contribute to the metal extraction process, but the mechanisms of this plant–microbe interaction are not yet understood. In this study ten rhizosphere isolates obtained from heavy metal accumulating willows affiliating with Pseudomonas, Janthinobacterium, Serratia, Flavobacterium, Streptomyces and Agromyces were analysed for their effect on plant growth, Zn and Cd uptake. In plate assays Zn, Cd and Pb resistances and the ability of the bacteria to produce indole-3-acetic acid (IAA), 1-amino-cyclopropane-1-carboxylic acid deaminase (ACC deaminase) and siderophores were determined. The isolates showed resistance to high Zn concentrations, indicating an adaptation to high concentrations of mobile Zn in the rhizosphere of Salix caprea. Four siderophore producers, two IAA producers and one strain producing both siderophores and IAA were identified. None of the analysed strains produced ACC deaminase. Metal mobilization by bacterial metabolites was assessed by extracting Zn and Cd from soil with supernatants of liquid cultures. Strain Agromyces AR33 almost doubled Zn and Cd extractability, probably by the relase of Zn and Cd specific ligands. The remaining strains, immobilized both metals. When Salix caprea plantlets were grown in γ-sterilized, Zn/Cd/Pb contaminated soil and inoculated with the Zn resistant isolates, Streptomyces AR17 enhanced Zn and Cd uptake. Agromyces AR33 tendentiously promoted plant growth and thereby increased the total amount of Zn and Cd extracted from soil. The IAA producing strains did not affect plant growth, and the siderophore producers did not enhance Zn and Cd accumulation. Apparently other mechanisms than the production of IAA, ACC deaminase and siderophores were involved in the observed plant–microbe interactions.     

呼和浩特市大青山白桦根际土壤细菌群落结构研究

采用高通量测序技术对天然次生林生态系统演替过程中先锋树种白桦的根际土壤细菌多样性及群落结构进行了分析。研究结果表明:白桦根际土壤细菌隶属于28门、90纲、126目、213科、286属,在3个采样地中排名前8的优势细菌门的相对丰度均大于1%,分别为变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)、芽单胞菌门(Gemmatimonadetes)、绿弯菌门(Chloroflexi)、硝化螺旋菌门(Nitrospirae)、疣微菌门(Verrucomicrobia)和拟杆菌门(Bacteroidetes)。各样地中前3个门的相对丰度之和均在60%以上。对白桦根际土壤细菌的α多样性指数、门水平的聚类热图以及PCoA聚类结果的分析表明,3个采样地中,小井沟(B2)和哈达门森林公园(C2)白桦根际土壤细菌的物种组成更为接近,与井儿梁(A2)的物种组成有一定差异;且小井沟和哈达门森林公园的物种多样性及丰度(ACE指数)显著高于井儿梁,表明细菌对不同环境的适应能力有明显差异。对细菌群落结构与土壤理化性质的RDA分析及相关性分析表明,环境因子对白桦根际土壤细菌的影响顺序为:全氮TN酸碱度pH含水量WC速效钾AK硝态氮NN铵态氮AN有机质OM有效磷EP,其中,TN、pH和WC是白桦根际土壤优势细菌的主要影响因子。研究结果为深入认识森林生态系统中根际土壤细菌的群落结构和影响因子提供了理论依据。     

白马雪山云南黄芪与灰毛康定黄芪根际微生物物种多样性及抗生物膜活性菌株筛选

【背景】细菌生物膜是造成病原菌耐药性增强和持续感染的主要因素,但目前尚无针对抗菌膜的特效药物。特境植物根际微生物可产生大量具有提高宿主免疫功能的活性成分,极具抗生物膜药源开发潜力。【目的】了解滇西北高寒特境白马雪山分布的云南黄芪与灰毛康定黄芪植物根际微生物的物种多样性,并对可培养菌株进行抑菌与抗生物膜活性筛选。【方法】采用宏基因组技术结合传统微生物培养方法,对采自我国云南迪庆藏族自治州德钦县白马雪山的云南黄芪与灰毛康定黄芪的根际微生物进行物种多样性研究,并通过“孔板法”测定其可培养菌株发酵液乙酸乙酯粗浸膏的抗菌、抗生物膜活性。【结果】宏基因组测序结果显示,云南黄芪根际土壤样本中的微生物来自6门7纲8目8科9属10种,其中栖热菌属为优势菌群;灰毛康定黄芪根际土壤样本中的微生物来自6门8纲10目11科14属15种,其中慢生根瘤菌属为优势菌群。通过纯培养共获得145株可培养菌株,包括112株细菌和33株真菌。其中,云南黄芪根际细菌59株,共计16属35种,优势属为假单胞菌属和链霉菌属;根际真菌19株,共计4属5种,优势属为曲霉属;灰毛康定黄芪根际细菌53株,归属于16属29种,优势属为芽孢杆菌属与寡养单胞菌属;根际真菌14株,归属于3属4种,优势属为曲霉属。从不同种水平上选择51株细菌和7株真菌为代表菌株进行抗生素药源评估,发现5株细菌及1株真菌发酵液的乙酸乙酯粗浸膏具有中等至较强的抗革兰阳性菌活性,而且其中4株具有抗MRSA生物膜活性,最终确定了链霉属放线菌Streptomyces fulvissimus KTA1和曲霉属真菌Aspergillus fumigatus YNF5为潜力活性菌株。【结论】首次报道了滇西北地区高寒特境黄芪属植物根际微生物具有较好的物种多样性,而且具有一定的抗生素药用资源开发潜力。本研究对滇西北高寒特境特色植物来源的微生物资源开发利用与保护具有重要的借鉴意义。     

基于高通量测序的连栽木麻黄根际土壤细菌群落变化研究

选取3个不同连栽代数(第一代First rotation plantation,FCP;第二代Second rotation plantation,SCP;第三代Third rotation plantation,TCP)木麻黄林地根际土壤为研究对象,通过IonS5~(TM)XL二代测序系统,从根际土壤微生物角度探究木麻黄连栽障碍形成机制。结果显示:从3个不同连栽代数木麻黄根际土壤中总共得到338560条有效序列,将其注释为17627个操作分类单元(Operational Taxonomic Units,OTUs)。α多样性指数表明,木麻黄根际土壤细菌群落的Simpson、Chao1、ACE指数随着连栽代数增加而下降,Observed species、Shannon指数呈现先增加后减少的趋势。β多样性指数表明,根际土壤中FCP与SCP之间的细菌群落多样性差异相对较大。UPGMA聚类分析结果阐明,木麻黄根际土壤FCP与SCP、TCP存在较大差异。优势细菌在属水平的热图分析结果表明,不同连栽代数木麻黄根际土壤细菌群落结构存在一定差异。随着木麻黄连栽代数增加,根际土壤中慢生根瘤菌属(Bradyrhizobium)的相对丰度呈上升趋势;与之相反,热酸菌属(Acidothermus)、根微菌属(Rhizomicrobium)、酸杆菌属(Acidibacter)、布氏杆菌属(Bryobacter)随连栽代数增加而下降;其中,与营养循环相关的有益菌属Rhizomicrobium的相对丰度随连栽代数增加而降低约311.49%、282.16%,而酸杆菌属(Acidibacter)的相对丰度随之降低约176.07%、284.54%。因此,木麻黄连栽障碍问题可能是由于根际土壤微生物群落结构失衡导致的,从而降低了森林的生态效益,使平均木生物量、林分生物量及林分净生产力下降。研究结果对揭示木麻黄连栽障碍形成的原因具有一定参考价值。     

The community composition of root-associated bacteria of the tomato plant

The objective of this study was to characterize the bacterial community composition in the bulk soil, rhizosphere soil and root tissue of the tomato plant (Lycopersicum esculentum Mill). 16S ribosomal DNA (rDNA) from the bacterial community was amplified using PCR, and sequence analysis of 16S rDNA clones was subsequently used for bacterial identification and phylogenetic classification. Phylogenetic analysis of clones (total of 68) from the bulk soil, rhizosphere and root tissues showed that about 50% of the bacteria belonged to the α-, β-, γ-, and δ-Proteobacteria or Cytophaga–Flavobacterium–Bacteroides (CFB) phyla, with only one high G+C clone identified. A number of diverse bacteria were identified within Proteobacteria, while 87% of the bacteria belonged to the genus Flavobacterium within the CFB phylum, which is a unique finding for tomato plants. Our results will be of interest to those wanting to identify bacteria that can promote plant growth or resistance to diseases.     

Degradation of polychlorinated biphenyl (PCB) by a consortium obtained from a contaminated soil composed of Brevibacterium,Pandoraea and Ochrobactrum

An indigenous polychlorinated biphenyl (PCB)-degrading bacterial consortium was obtained from soils contaminated by transformer oil with a high content of PCBs. The PCB degrader strains were isolated and identified as Brevibacterium antarcticum, Pandoraea pnomenusa, and Ochrobactrum intermedium by 16S rRNA gene sequence phylogenetic analysis. The PCB-degrading ability of the consortium and of individual strains was determined by using GC/MS. The PCB-degrading capacities of the consortium were evaluated for three concentrations of transfomer oil ranging from 55 to 152 μM supplemented with 0.001% biphenyl and 0.1% of Tween 80 surfactant. PCB biodegradation by the consortium was favored in the presence of both additives and the greatest extent of biodegradation (67.5%) was obtained at a PCB concentration of 55 μM. Each bacterial species exhibited a particular pattern of degradation relating to specific PCB congeners. Isolated strains showed a moderate degradation capability towards tetra-, hepta-, and octa-chlorobiphenyls; although no effect on penta-, hexa-, and nona-chlorobiphenyls was observed. Recently, PCB degradation capacity was recognized in a Pandorea member; however, this is the first study that describes the ability of Brevibacterium and Ochrobactrum species to degrade PCBs.     

Frankia in the rhizosphere of nonhost plants: A comparison with root-associated N2-fixing Enterobacter,Klebsiella and Pseudomonas

Bacterial growth in the rhizosphere and resulting changes in plant growth parameters were studied in small aseptic seedlings of birch (Betula pendula and B. pubescens) and grasses (Poa pratensis and Festuca rubra). The seedlings were inoculated with three Frankia strains (Ai1a and Ag5b isolated from native Alnus root nodules and Ai17 from a root nodule induced by soil originating from a Betula pendula stand), and three associative N₂-fixing bacteria (Enterobacter agglomerans, Klebsiella pneumoniae and Pseudomonas sp., isolated from grass roots). Microscopic observations showed that all the Frankia strains were able to colonize and grow on the root surface of the plants tested without addition of an exogenous carbon source. No net growth of the associative N₂-fixers was observed in the rhizosphere, although inoculum viable counts were maintained over the experimental period. Changes in both the biomass and morphology of plant seedlings in response to bacterial inoculation were recorded, which were more dependent on the plant species than on the bacterial strain.     

健康与感染青枯病烟株根际土壤与茎秆细菌群落结构与多样性

【目的】了解健康烟株与感染青枯病烟株在根际土壤、茎杆发病部位、茎杆病健交界部位以及未发病茎杆的细菌群落结构与多样性。【方法】分别对土壤与茎杆样品中细菌的16S rRNA基因V3-V4区进行扩增,采用Illumina MiSeq测序技术对扩增片段进行高通量测序,然后对健康烟株与感染青枯病烟株不同部位细菌群落结构与多样性进行分析。【结果】感染青枯病烟株发病茎杆及根际土壤的细菌群落多样性高于健康烟株茎杆及其根际土壤样品,病健交界茎杆样品细菌群落多样性低于健康烟株。变形菌门(Proteobacteria)在所有样品中均为优势菌门;所有烟株根际土壤的优势菌门为拟杆菌门(Bacteroidetes)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)和绿弯菌门(Chloroflexi);健康烟株茎杆部位的优势菌门为蓝细菌门(Cyanobacteria);感染青枯病烟株发病茎杆和病健交界茎杆部位的优势菌门为蓝细菌门(Cyanobacteria)和厚壁菌门(Firmicutes)。所有根际土壤样品的优势菌属为劳尔氏菌属(Ralstonia)、假单胞菌属(Pseudomonas)、鞘脂单胞菌属(Sphingomonas)、黄杆菌属(Flavobacterium)和代尔夫特菌属(Delftia),而感染青枯病烟株根际土壤的劳尔氏菌属(Ralstonia)和假单胞菌属(Pseudomonas)相对丰度显著高于健康烟株根际土壤,鞘脂单胞菌属相对丰度显著低于健康烟株根际土壤。烟株茎杆的优势菌属为劳尔氏菌属和假单胞菌属等。感染青枯病烟株病健交界茎杆中劳尔氏菌属、肠杆菌属(Enterobacter)和泛菌属(Pantoea)相对丰度显著低于健康烟株样品。【结论】健康与感染青枯病烟株茎杆样品细菌群落的丰富度和多样性明显低于相应的根际土壤样品。较健康烟株而言,感染青枯病烟株根际土壤和茎杆样品细菌群落丰富度和多样性均表现出不同程度地增加,且根际土壤细菌群落结构变化较茎杆样品明显,而病健交界茎杆样品细菌群落丰富度和多样性降低。烟草青枯病为典型土传病害,其病原茄科劳尔氏菌尽管能在烟株维管束中蔓延扩增,但主要还是分布于土壤中;它的存在似乎对土壤细菌群落的影响大于茎杆样品的。该研究结果提示对于青枯病的防治不能局限于烟株本身,田间土壤也应加大防治力度。     

Competition alters plant species response to nickel and zinc

Phytoextraction can be a cost-efficient method for the remediation of contaminated soils. Using species mixtures instead of monocultures might improve this procedure. In a species mixture, an effect of heavy metals on the species' performance can be modified by the presence of a co-occuring species. We hypothesised that (a) a co-occuring species can change the effect of heavy metals on a target species, and (b) heavy metal application may modifiy the competitive behaviour between the plants. We investigated these mechanisms in a greenhouse experiment using three species to serve as a model system (Carex flava, Centaurea angustifolia and Salix caprea). The species were established in pots of monocultures and mixtures, which were exposed to increasing concentrations of Ni and Zn, ranging from 0 to 2,500 mg/kg. Increased heavy metal application reduced the species' relative growth rate (RGR); the RGR reduction being generally correlated with Ni and Zn concentrations in plant tissue. S. caprea was an exception in that it showed considerable Zn uptake but only moderate growth reduction. In two out of six cases, competitors significantly modified the influence of heavy metals on a target species. The interaction can be explained by an increased uptake of Zn by one species (in this case S. caprea) that reduced the negative heavy metal effect on a target species (C. flava). In two further cases, increasing heavy metal application also altered competitive effects between the species. The mechanisms demonstrated in this experiment could be of relevance for the phytoextraction of heavy metals. The total uptake of metals might be maximised in specific mixtures, making phytoextraction more efficient.     

Phytoextraction of Cd and Zn from agricultural soils by Salix ssp. and intercropping of Salix caprea and Arabidopsis halleri

Contamination of agricultural topsoils with Cd above guideline values is of concern in many countries throughout the world. Extraction of metals from contaminated soils using high-biomass, metal-accumulating Salix sp. has been proposed as a low-cost, gentle remediation strategy, but reasonable phytoextraction rates remain to be demonstrated. In an outdoor pot experiment we assessed the phytoextraction potential for Cd and Zn of four willow species (Salix caprea, S. fragilis, S. × smithiana, S. × dasyclados) and intercropping of S. caprea with the hyperaccumulator Arabidopsis halleri on three moderately contaminated, agricultural soils. Large concentrations of Cd (250 mg kg⁻¹) and Zn (3,300 mg kg⁻¹) were determined in leaves of Salix × smithiana grown on a soil containing 13.4 mg kg⁻¹ Cd and 955 mg kg⁻¹ Zn, resulting in bioaccumulation factors of 27 (Cd) and 3 (Zn). Total removal of up to 20% Cd and 5% Zn after three vegetation periods were shown for Salix × smithiana closely followed by S. caprea, S. fragilis and S. × dasyclados. While total Cd concentrations in soils were reduced by up to 20%, 1 M NH₄NO₃-extractable metal concentrations did not significantly decrease within 3 years. Intercropping of S. caprea and A. halleri partly increased total removal of Zn, but did not enhance total Cd extraction compared to single plantings of S. caprea after two vegetation periods.     

青枯病易感和钝感桑树品种根际土壤真菌群落结构比较

为研究青枯病易感和钝感桑树品种植株根际土壤真菌群落组成,该研究以ITS1F和ITS2R为引物,基于高通量测序技术对桑树青枯病易感品种(台湾长果桑,SM)和桑树青枯病钝感品种(桂桑12号,IM)植株根际土壤真菌群落结构进行分析。结果表明：(1)两个品种间指示真菌丰富度的ACE、Chao1指数及表征多样性的Shannon指数无显著差异,门分类水平,被孢霉门(Mortierellomycota)和球囊菌门(Glomeromycota)是青枯病钝感桑树品种植株根际土壤中特有的优势真菌门;而属分类水平,Apiotrichum、地丝菌属(Geotrichum)、足放线病菌属(Scedosporium)和腐质霉属(Humicola)等是青枯病易感桑树品种植株根际土壤中富集的特有优势真菌属。(2)青枯病易感桑树品种植株根际土壤中,缺失了被孢霉门、球囊菌门真菌,以及被孢霉属(Mortierella)、镰刀菌属(Fusarium)、曲霉菌属(Aspergillus)和毛壳菌属(Chaetomium)等具有生防功能的优势真菌门属,可能是其易感青枯病的重要原因。(3)根据真菌群落对同类环境资源的利用途径进行功...     

两种镉积累型小麦根际微生物群落结构及功能多样性

为探究不同积累型小麦品种对根际微生物群落结构及功能多样性的影响,以镉低积累型小麦济麦22和镉高积累型小麦冀5265为研究材料,采用分离培养法和Biolog-Eco微平板法分析根际细菌数量、可培养优势群落结构以及微生物群落功能多样性。结果表明：污染土壤济麦22根际总细菌数量和抗Cd细菌数量均显著高于冀5265,而非污染土壤中两品种间无差异。污染土济麦22根际发现较多产脲酶和高镉抗性菌株(200 mg/L)。污染土济麦22根际优势菌多为Arthrobacter sp.和Bacillus sp.,冀5265根际优势菌主要为Streptomyces sp.;非污染土济麦22与冀5265根际优势菌群相似,均以Bacillus sp.为主。Biolog试验结果表明,两个小麦品种根际微生物群落对碳源的利用能力存在差异,济麦22根际微生物AWCD值、Mc Intosh指数、Shannon-Wiener指数、Simpson指数在污染土和无污染土中均显著高于冀5265。因此,污染土壤中不同积累型小麦品种根际微生物群落结构及功能多样性均存在差异,该研究结果对于揭示高低积累型小麦根际微生物机制提供了重要参考依...