荒漠草原植物骆驼蓬根际土壤细菌群落分析北大核心CSCD

骆驼蓬（Peganum harmala L.）具有较强耐旱抗寒特性,在维护生态环境中发挥着重要作用。为了解其生态适应及与环境相互作用机制,采用高通量测序和纯培养方法研究了甘肃白银荒漠草原区骆驼蓬根际土壤细菌群落特征,并与周边土壤进行了对比。结果表明：骆驼蓬根际土壤主要优势细菌群为放线菌门（Actinobacteria）30.01%、变形菌门（Proteobacteria）23.98%、拟杆菌门（Bacteroidetes）11.53%、酸杆菌门（Acidobacteria）10.19%。周边荒漠草原土壤主要优势细菌群为放线菌门55.05%、变形菌门21.11%、酸杆菌门6.07%。可培养细菌类群包括厚壁菌门（Firmicutes）、变形菌门、放线菌门,其中根际土壤分离的优势菌为短杆菌属（Brevibacterium）23.53%、芽孢杆菌属（Bacillus）23.53%、假单胞菌属（Pseudomonas）17.65%,周边土壤可培养细菌的优势种群为节杆菌属（Arthrobacter）37.50%、芽孢杆菌属18.75%、假单胞菌属12.50%。骆驼蓬根际微生物群落组成和结构与周边土壤有显著差异,根际土壤微生物数量及多样性指数明显高于非根际土壤。研究结果对了解荒漠植物与根际微生物之间相互作用,揭示土壤微生物促进植物根际土壤物质循环转化作用,筛选促生长有益微生物,为加强荒漠草原生态保护提供科学依据。     

科尔沁沙地水盐处理对油莎豆农田土壤细菌群落及植株生理特性的影响

为揭示水盐处理下科尔沁沙地土壤细菌群落结构及其对油莎豆（Cyperus esculentus）的影响。以吉林省前郭尔罗斯灌区油莎豆农田为研究对象,开展水、盐双因素（水处理：50%、70%、100%标准灌溉定额;盐处理：无盐胁迫、轻度盐胁迫、中度盐胁迫）随机区组野外控制试验,构建土壤细菌分子生态网络筛选关键菌种,并研究揭示其与油莎豆生长的相互关系。结果表明：（1）油莎豆农田土壤细菌优势菌门为变形菌门（Proteobacteria）(22.85%±3.80%)、酸杆菌门（Acidobacteriota）(20.02%±3.21%)和放线菌门（Actinobacteriota）(18.85%±2.41%)。优势菌属为RB41属、鞘氨醇单胞菌属（Sphingomonas）和红色杆菌属（Rubrobacter）。水盐环境对土壤细菌Alpha多样性无显著影响（P>0.05）。（2）100%标准灌溉定额灌溉处理细菌种间共存关系更强,50%标准灌溉定额灌溉处理细菌种间互作程度、连接紧密度最高。无盐胁迫细菌群落生态网络复杂度、互作程度最高,中度盐胁迫细菌物种之间的共存关系更强。（3）随灌溉量增加,...     

种稻年限对盐渍化土壤理化性质和细菌群落多样性的影响

为了解盐渍化土壤长期种稻引起土壤微生物和理化性质的变化特征,选取了种植水稻0、1、6、12、21 a的田块,用旱地(种植玉米)土壤作对照,利用Illumina Hiseq高通量测序技术解析不同种稻年限土壤细菌群落结构的特征,并分析了土壤理化因子与细菌群落结构的关系。结果表明:变形菌门、拟杆菌门、放线菌门是所有样点土壤细菌群落的优势种类,其中,变形菌门占总量的36.39%～53.20%,γ-变形菌纲相对丰度在0 a种稻的土壤中显著高于其他样点(P0.05)。变形菌门相对丰度在种稻1 a的土壤中含量较高,达到45.26%;拟杆菌门的相对丰度在种稻12 a和21 a土壤中较高,分别为20.25%和20.44%;放线菌门相对丰度在0 a土壤中显著高于其他样点(P0.05),为17.90%。在属水平,布赫纳氏菌属是所有样点的优势属。α多样性指数结果显示:种稻12 a的土壤细菌群落多样性和丰富度都显著低于其他样点,分别低于对照17.06%、85.73%、82.88%。土壤理化性质测定结果表明:全氮和硝态氮在旱地土壤中含量最高;微生物碳和电导率在种稻12 a的土壤中最低,低于对照101.89%、23.25%;有机碳在21 a种稻土壤中含量最高,高于对照29.03%;pH值在21 a种稻土壤中最低,低于对照组1.05%。Pearson相关性分析表明:微生物量碳和土壤电导率对细菌多样性指数的影响显著。冗余分析结果表明,土壤电导率值、微生物碳和硝态氮是影响盐渍化稻作土壤细菌群落结构的主要因子。研究表明,随着种稻年限的延长土壤细菌群落和理化性质发生显著变化,土壤生境呈明显的改善趋势。     

进境秘鲁朱顶红种球携带菌群组成及潜在致病菌初探

为查明进境朱顶红种球携带真菌和细菌菌群组成情况及潜在致病菌种类,本研究对宁波口岸5批次进境朱顶红种球进行取样,获得根部和顶部样本各5份,采用基于rRNA ITS和16S rRNA基因的Pacbio扩增子测序技术、生物信息学分析方法和分离培养技术,比较了供试样本中的菌群组成及潜在致病菌种类。对朱顶红种球根部与顶部的真菌菌群组成分析结果显示,在门水平上,子囊菌门（Ascomycota）的真菌丰度均为最高;在属水平上,青霉属（Penicillium）是最丰富的真菌菌群,在种球根部和顶部的平均相对丰度分别为68.73%和26.20%;在种水平上,短密青霉（Penicillium brevicompactum）是最丰富的真菌种类,平均相对丰度分别为58.54%和24.02%。细菌菌群组成分析结果显示,在门水平上,变形菌门（Proteobacteria）的细菌丰度最高;在属水平上,泛生菌属（Pantoea）是最丰富的细菌菌群,在种球根部和顶部的平均相对丰度分别为66.55%和74.50%;在种水平上,成团泛菌（Pantoea agglomerans）是最丰富的细菌种类,平均相对丰度分别为52.18...     

云南省不同海拔区草地贪夜蛾幼虫肠道与粪便细菌多样性

为探明草地贪夜蛾Spodoptera frugiperda不同海拔种群的幼虫肠道及粪便细菌组成,采用分离培养法、形态特征及16S rDNA测序分析法对云南省5个海拔22个草地贪夜蛾种群的幼虫肠道及粪便细菌进行分离培养、鉴定。结果表明,从不同海拔种群的幼虫肠道和粪便中分别获得可培养细菌4门15科22属45种和4门13科18属36种,优势菌门均为变形菌门和厚壁菌门。不同海拔种群的幼虫肠道和粪便细菌组成均不同,500 m以下、1 001～1 500 m、1 501～2 000 m和2 000 m以上4个海拔种群的幼虫肠道细菌优势属和优势种分别为肠球菌属Enterococcus和铅黄肠球菌Enterococcus casseliflavus,500～1 000 m海拔种群的优势属和优势种分别为克雷伯氏菌属Klebsiella和变栖克雷伯氏菌Klebsiella variicola;500 m以下、500～1 000 m、1 001 m以上海拔种群的幼虫粪便细菌优势属分别为假单胞菌属Pseudomonas、克雷伯氏菌属和肠球菌属,优势种分别为韩国假单胞菌Pseudomonas koreensis...     

生物炭、三叶草和蚯蚓种养对西瓜根际土壤细菌群落多样性的影响

为探究生物炭、三叶草和蚯蚓种养三种施用方式对西瓜根际土壤细菌群落多样性、功能预测及养分的影响,开展田间小区试验,设置对照(CK)、生物炭（B）、三叶草（T）、蚯蚓种养（V）、生物炭+蚯蚓种养（BV）、三叶草+蚯蚓种养（TV）、三叶草+生物炭（BT）和三叶草+生物炭+蚯蚓种养（BTV）等8个处理。结果表明：不同处理对西瓜根际土壤养分具有显著影响,BV处理土壤速效钾含量最高（383.41 mg·kg^-1）,TV处理土壤全氮含量最高（0.79 g·kg^-1）、BTV处理土壤速效磷含量最高（427.51 mg·kg^-1）,分别较CK处理提高102.23%、75.56%、23.88%。BTV处理Shannon指数显著高于其他处理;TV处理Simpson指数较T处理提高56.52%;B处理的ACE和Chao1指数较BTV处理分别提高10.95%和12.59%。不同土壤处理影响细菌群落组成和相对丰度,其中变形菌门、放线菌门、绿弯菌门和厚壁菌门为优势菌门。与CK相比,BTV处理的变形菌门和放线菌门相对丰度分别提高47.85%和30.47%,而酸杆菌门相对丰度降低48.36%。PICRUST2功能预测分析表明,BTV处理根际土壤细菌群落中新陈代谢、氨基酸代谢和全局概览通路等功能的活性加强,其活性微生物在“生物炭—三叶草—蚯蚓种养—西瓜”复合生境中起重要作用。综上,不同土壤处理方式改善了土壤细菌群落多样性和土壤养分,其中生物炭和三叶草配合蚯蚓种养施用的综合效果最好。     

轮作休耕模式对土壤细菌群落的影响

以黄土高原半干旱区9种轮作休耕模式土壤为研究对象，分别设残膜覆盖（T₂1）、伏天深耕（T₂2）、施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续休耕3 a（T₂3）、施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续种植豌豆3 a并在盛花期翻压还田（T₂4）、施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续3 a种植豌豆（每kg豌豆种子拌根瘤菌粉8.5 g）并在盛花期翻压还田（T₂5）、玉米秸秆粉碎（还田量7 500 kg·hm^-2）+施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续休耕3 a（T₂6）、玉米秸秆粉碎（还田量7 500 kg·hm^-2）+施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续3 a种植毛苕子并在盛花期翻压还田（T₂7）、玉米秸秆粉碎（还田量7 500 kg·hm^-2）+施牛羊粪（7 500 kg·hm^-2）+深翻耕（30 cm）+连续3 a种植毛苕子并在盛花期翻压还田（T₂8）等8个处理，以连续休耕3 a为对照（CK）,采用16S rRNA扩增子测序技术对土壤细菌群落组成、丰度和多样性等特征进行研究，分析了土壤养分与细菌种群多样性的相关关系。结果表明，9种休耕轮作模式下，土壤细菌群落中相对丰度较高的前5位菌门依次为变形菌门（Proteobacteria）（26.33%～37.33%）、酸杆菌门（Acidobacteria）（17.93%～21.43%）、放线菌门（Actinobacteria）（12.42%～19.41%）、芽单胞菌门（Gemmatimonadetes）（6.98%～10.99%）和绿弯菌门（Chloroflexi）（6.48%～10.50%）。其中T₂1、T₂5处理显著升高了硝化螺旋菌门的相对丰度（分别为50.04%和42.44%），T₂2处理显著提高了变形菌门和拟杆菌门的相对丰度（分别为31.51%和159.96%），T₂6、T₂7处理显著增加了芽单胞菌门的相对丰度（分别为28.36%和28.33%），T₂8处理显著增高了奇古菌门的相对丰度（519.79%）。不同轮作休耕模式的土壤全氮含量均高于CK。细菌群落丰富度指数除T₂7处理外，其余处理均高于CK。冗余分析和Monte Carlo置换检验结果显示，土壤全氮、全钾、速效氮含量对土壤细菌群落结构影响显著（P＜0.05）。     

冬灌制度对膜下滴灌棉田土壤理化性质、酶活性和微生物群落的影响

为明确不同冬灌制度的应用效果，以南疆膜下滴灌棉田为研究对象，选取每年冬灌处理（CK）、不冬灌处理（H1）及隔年冬灌处理（H2）3种冬灌制度，结合高通量测序技术对冬灌后土壤的理化性质、生物学性质以及微生物群落组成进行测定与分析。结果表明：（1）各处理间0~20 cm土层土壤总盐含量无显著差异，与CK相比，H1和H2处理显著降低了脲酶（0.96%~1.35%）和转化酶活性（1.17%）以及微生物量氮含量（4.21%~7.03%），但H2处理显著提高了土壤有机质（14.30%）、全氮（14.29%）、全磷（4.55%）和全钾（7.40%）含量；H1处理显著降低了土壤有机质（6.03%）、全磷（12.5%）和水分（23.08%）含量，提高了微生物量碳氮比（7.37%）。（2）不同处理下细菌群落的丰度和多样性以及真菌群落的丰度无显著差异，但与CK相比，H1和H2处理显著提高了真菌的辛普森指数（4.12%~ 4.55%）。此外，H1较CK处理提高了细菌放线菌门（Actinobacteria）、酸杆菌门（Acidobacteria）、绿弯菌门（Chloroflexi）和真菌担子菌门（Basidiomycota）的相对丰度，H2较CK处理提高了细菌变形菌门（Proteobacteria）、芽单胞菌门（Gemmatimonadetes）和真菌被孢霉门（Mortierellomycota）的相对丰度。（3）相关性分析结果表明细菌的群落结构主要受微生物量碳含量的影响，真菌的群落结构和多样性分别受转化酶和脲酶活性的影响。在无法保证每年冬灌用水的情况下，隔年冬灌更有利于保障膜下滴灌棉田的土壤耕地质量。     

准格尔露天矿区复垦对土壤细菌多样性的影响研究

运用PCR-DGGE技术对我国准格尔露天煤矿不同复垦时间土壤细菌组成及其多样性变化进行了研究,结果表明:1)复垦区的土壤细菌主要是厚壁菌门、拟杆菌门、放线菌门、变形菌门、酸杆菌门、芽单胞菌门和未知细菌类7类,其中,放线菌门、拟杆菌门和变形菌门为优势类群,占到全部细菌的81.2%;2)成功完成矿山土壤样品微生物总DNA提取和PCR-DGGE的分析检测,在69个测序序列中,不可培养细菌占到总数的62.3%;3)各复垦阶段存在共有细菌类群,但更多的细菌类群是随复垦时间不同而发生变化的。4)豆科-禾本科牧草种植区的土壤细菌多样性指数要高于乔灌草类型,这可能与豆科植物中丰富的根瘤菌利于土壤细菌生长发育有关。     

生长年限对甘肃贝母根际土壤细菌群落结构的影响

采用Illumina MiSeq高通量测序技术对撂荒地（CK）、生长1 a（BM-1Y）、3 a（BM-3Y）和5 a（BM-5Y）的甘肃贝母根际土壤细菌16S rRNA基因V3-V4可变区进行测序分析，探究不同生长年限甘肃贝母对根际土壤细菌群落结构的影响。结果表明：生长年限对甘肃贝母土壤理化因子和细菌菌群均有影响，其中BM-5Y处理显著降低了土壤有机质（OM）、水解氮（HN）和速效磷（AP）的含量（P＜0.05），较CK处理分别降低了22.76%、9.28%、51.25%；BM-5Y处理显著降低根际土壤细菌多样性（P＜0.05），其中OUT数、PD值及Chao I指数较CK处理分别降低了7.23%、6.79%、6.47%。生长年限改变了细菌群落在门和属水平的群落组成，但各生长年限中的优势菌门（相对丰度＞5%）相对稳定，均为放线菌门（Actinobacteria）、变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）和绿弯菌门（Chloroflexi），其在CK、BM-1Y、BM-3Y和BM-5Y处理中的相对丰度总和分别为82.28%、84.16%、83.12%和82.30%。土壤pH、OM、HN、AP及AK含量是驱动根际土细菌群落的主要环境因子，其程度大小为：pH＞AK＞HN＞AP＞OM。土壤理化因子与各优势细菌门的相关性不同，pH与放线菌门（Actinobacteria）和芽单胞菌门（Gemmatimonadetes）呈显著负相关（P＜0.05），OM、HN和AP均与厚壁菌门（Firmicutes）呈显著负相关（P＜0.05）。综上，甘肃贝母生长年限延长（BM-5Y）会显著降低土壤的养分含量和细菌群落的多样性。     

Epiphytic colonization of pear stigmas and hypanthia by bacteria during primary bloom

ABSTRACT Pear blossoms were sampled during various stages of bloom in 1991 and 1992 from orchards at Cashmere, WA, and Corvallis and Medford, OR, for epiphytic populations of culturable bacteria. On stigmatic surfaces, bacteria were isolated from 2 to 32% of blossoms prior to petal expansion and from 47 to 94% of blossoms by petal fall. In general, a lower percentage of hypanthia than stigmas supported bacterial populations. Randomly selected bacteria isolated at population levels of >/=10(4) CFU/tissue were identified by fatty acid methyl ester analysis. Diverse genera of gram-negative and -positive bacteria were identified from the Medford and Cashmere field sites. Pseudomonas syringae and Pseudomonas viri-diflava were isolated from all sites and were the predominant species detected at Corvallis, where they were isolated from 28% of the blossoms sampled on a given date. Because most pear blossoms do not support detectable populations (>/=10(2) CFU/tissue) of culturable bacteria prior to petal expansion, we speculate that introduced biocontrol agents may become established with minimal competition from indigenous epiphytes at early bloom stages.     

Comparison of sandy soils suppressive or conducive to ectoparasitic nematode damage on sugarcane

ABSTRACT Two South African sandy soils, one suppressive and the other conducive to ectoparasitic nematode damage on monoculture sugarcane, were compared. Analysis of field transects indicated that the suppressive soil displayed a comparatively higher population of the weak ectoparasite Helicotylenchus dihystera, whose predominance among ectoparasitic nematodes is known to limit yield loss caused by more virulent phytonematodes. Soil type was identical at both sites (entisols), but the suppressive soil had a higher organic matter content and a lower pH, which correlated with H. dihystera population data. In contrast, microclimatic differences between the two field sites were unlikely to be responsible for the suppressive or conducive status of the soils, as shown in a greenhouse experiment. The two soils exhibited a bacterial community of the same size but with different genetic structures, as indicated by automated ribosomal intergenic spacer analysis (RISA). The number of culturable fluorescent pseudomonads was higher for the conducive soil, probably because extensive root damage caused by ectoparasitic nematodes favored proliferation of these bacteria. This study shows that apparently small differences in soil composition between fields located in the same climatic area and managed similarly can translate into contrasted nematode communities, ectoparasitic nematode damage levels, and sugarcane yields.     

马铃薯腐烂茎线虫28S rDNA-D2/D3区序列分析

 我国危害甘薯的马铃薯腐烂茎线虫rDNA-ITS基因片段长度存在A型(900bp)和B型(1100bp)2个类型,A型腐烂茎线虫群体的ITS片段比B型群体少200bp。为了进一步研究这2种类型群体的发育关系,本文用线虫通用引物D2A和D3B对来自国内的21个马铃薯腐烂茎线虫群体和1个韩国的马铃薯腐烂茎线虫28SrDNA-D2/D3区进行了PCR扩增,均产生大小一致的片段,长度约为780bp,克隆、测序后用DNAMAN5.2软件和MEGA4软件进行分析比对,结果表明我国21个马铃薯腐烂茎线虫群体28SrDNA-D2/D3区只有20余个碱基的差异,相似率达97.2%。基于UPGMA构建的系统发育树很好地区分了马铃薯腐烂茎线虫A型和B型群体,展现出了群体的来源及发育关系。     

Bacterial community associated with the ambrosia beetle Platypus cylindrus on declining Quercus suber trees in the Alentejo region of Portugal

In Portugal, the oak pinhole borer Platypus cylindrus and its mycobiota have been associated with cork oak (Quercus suber) death, but no knowledge exists regarding the associated bacterial community. However, it is known that some bacteria are important for ambrosia beetle symbiosis and play a role in oak tree health. To explore the bacteria associated with this beetle and its host, with the ultimate goal of highlighting potential roles in oak decline, this study used a culture-dependent approach for strain isolation and phylogenetic identification using 16S rRNA gene sequencing and multilocus sequence analysis (MLSA). The bored galleries of different cork oak trees from a cork stand in Alentejo, together with the body and mycangia of adult beetles, were investigated. The samples revealed a diverse community comprising 500 isolates with 64 distinct types of bacterial colonies. Sixty-eight strains were selected for sequencing and used for phylogenetic analysis, 40 from wood galleries and 28 from beetles. Thirty-two genera of bacteria were identified, 18 of which were described for the first time within oak–beetle interactions. Major taxonomic groups were Actinobacteria in beetles and Enterobacterales in wood galleries. Although specific oak bacterial pathogens were not detected, a group of distinct strains detected in wood galleries, potentially belonging to a new Pectobacteriaceae species, were able to produce mild symptoms on cork oak plantlets. This study reports for the first time the biodiversity of culturable bacteria associated with the Q. suber–P. cylindrus interaction, their relevance to both organisms and the possible contribution to oak decline.     

水稻条纹病毒中国分离物和日本分离物RNA1片段序列比较

 首次测定了我国水稻条纹叶枯病常年流行区的云南楚雄(CX)及病害暴发区的江苏洪泽(HZ)的RSV 2个分离物RNA1片段的全长序列,这2个分离物RNA1片段的全长序列均为8970 nts。同源性分析结果表明,HZ与日本T分离物的亲缘关系较CX与T分离物的亲缘关系更为接近。通过对纤细病毒属病毒RNA1编码的依赖于RNA的RNA聚合酶(RdRp)氨基酸序列分析的结果表明,该蛋白除了具有RNA聚合酶特征的基元序列结构外,还存在mRNA的转录过程中所采取的加帽起始机制的保守性结构域位点,这表明,纤细病毒属病毒和布尼安病毒科病毒及甲型流感病毒一样,都是采取加帽起始机制进行转录的。     

Soft rot disease alters soil characteristics and root-associated,culturable microbial community of <Emphasis Type="Italic">Amorphophallus konjac</Emphasis>

To elucidate how soft rot disease affects soil characteristics and root-associated, culturable microorganisms in Amorphophallus konjac stands, the responses of soil around roots of A. konjac with soft rot disease were investigated in stands with and without soft rot. Changes in the root-associated culturable microbial community and diversity were investigated by dilution plating. Soil characteristics were compared between stands using standard techniques. A. konjac with soft rot had higher concentrations of available soil P and K, NH₄–N, organic matter and water content and lower pH compared with plants without. The community composition of root-associated culturable microorganisms differed between stands with and without soft rot. The microbial community associated with soft rot in A. konjac was characterized by four types of abundant microorganisms (Fusarium solani, Fusarium oxysporum, Pseudomonas chlororaphis subsp. aureofaciens and Stenotrophomonas pavanii) and three types of less-abundant microorganisms (Rhizobium radiobacter, Bacillus thuringiensis and Streptomyces cellulosae), and a small number of Bacillus and Streptomyces species in the rhizosphere and rhizoplane soils. Particular microbial combinations were diametrically opposed between plants with and without soft rot. The richness and diversity of root-associated culturable microorganisms were higher in the stand without soft rot than in the stand with soft rot. A. konjac soft rot led to obvious differences in the diversity and community composition of root-associated culturable microorganisms and in soil characteristics.     

卵菌与真菌Argonaute家族基因的生物信息学分析

 Argonaute蛋白广泛存在于真核生物与原核生物中,可在非编码小RNA或DNA的引导下,对完全匹配或部分匹配的靶标进行切割、翻译抑制或染色体修饰。本研究利用生物信息学对127种卵菌与真菌的基因组进行分析,旨在了解各个物种中AGO家族基因的数量、蛋白结构域、进化关系及转录模式等。结果发现,大部分卵菌与真菌的基因组中(51%)含有2个AGO基因,而疫霉菌和壶菌等平均含有4个以上。卵菌与真菌的AGO基因在进化上相互独立,多拷贝AGO基因可能是通过基因复制形成;大部分AGO基因具有6个可预测的功能域(即:N端、Linker 1、PAZ、Linker 2、MID和PIWI),并且在PAZ和PIWI功能域上,与核酸5'和3'端结合及与催化活性相关的氨基酸位点整体相对保守,仅个别位点存在一定的差异。侵染大豆过程中,大豆疫霉和终极腐霉的两对同源AGO基因具有保守的表达模式,且基因表达水平相对较高,可能具有相似的生物学功能。上述结果将为深入解析AGO介导的RNA干扰机制及生物学功能奠定基础。     

卵菌与真菌Argonaute家族基因的生物信息学分析

 Argonaute蛋白广泛存在于真核生物与原核生物中,可在非编码小RNA或DNA的引导下,对完全匹配或部分匹配的靶标进行切割、翻译抑制或染色体修饰。本研究利用生物信息学对127种卵菌与真菌的基因组进行分析,旨在了解各个物种中AGO家族基因的数量、蛋白结构域、进化关系及转录模式等。结果发现,大部分卵菌与真菌的基因组中(51%)含有2个AGO基因,而疫霉菌和壶菌等平均含有4个以上。卵菌与真菌的AGO基因在进化上相互独立,多拷贝AGO基因可能是通过基因复制形成;大部分AGO基因具有6个可预测的功能域(即:N端、Linker 1、PAZ、Linker 2、MID和PIWI),并且在PAZ和PIWI功能域上,与核酸5'和3'端结合及与催化活性相关的氨基酸位点整体相对保守,仅个别位点存在一定的差异。侵染大豆过程中,大豆疫霉和终极腐霉的两对同源AGO基因具有保守的表达模式,且基因表达水平相对较高,可能具有相似的生物学功能。上述结果将为深入解析AGO介导的RNA干扰机制及生物学功能奠定基础。     

Evolutionary Characterization of Two Lily Isolates of Cucumber mosaic virus Isolated in Japan and Korea

We analyzed the evolutionary histories of two lily strains of Cucumber mosaic virus (CMV) isolated in Japan and Korea (HL- and Ly2-CMVs). They share common biological characteristics in that their host ranges are very restricted perhaps from a unique adaptation to lily plants. Although HL and Ly2 were isolated independently from different lily species in separate countries, their RNA3 sequences had a very high sequence similarity (97%). The evolutionary relationships between the two isolates were characterized by comparing their phylogenetic trees for the 3a and CP genes. The two lily CMVs always formed a distinct cluster within subgroup IB in 3a, but within IA in CP. Together, the phylogenetic tree topology and the sequence identity between the two lily CMVs suggest that they evolved from a common progenitor. Received 5 November 2001/ Accepted in revised form 11 January 2002     

Impact of maize mucilage on atrazine mineralization and atzC abundance

Soil was amended with maize mucilage, a major rhizodeposit, to study its role on the number of culturable soil micro-organisms, the structure of the bacterial community, atrazine mineralization and atzC abundance. The maximal percentage of atrazine mineralization was lower for mucilage-amended than for water-amended soil. Total culturable soil bacteria and 16S rDNA copy number, measured by RT-PCR, presented similar values and were not significantly (P < 0.05) different among treatments. Mucilage applied at a rate of 70 microg C g(-1) dry soil day(-1) over two weeks did not modify the abundance of the total soil microflora. Global structure of soil bacterial communities revealed by RISA analysis was not modified by maize mucilage amendment. Abundance of atzC sequence was only augmented by mucilage addition at the beginning of the experiment. However, this increase was not sustainable in time, as atzC copy number increased in water-amended soil which, in turn, corresponded with the higher percentage of atrazine mineralization observed in this soil. Maize mucilage amendment alone contributed only to minor changes in the atrazine-degrading community in the studied soil.