薇甘菊根际可培养固氮菌和氨化细菌的分离鉴定与促生作用

【目的】固氮菌和氨化细菌是氮循环产生生物有效氮的关键起始环节,直接影响了外来入侵植物的生长速度和扩散进程。然而,关于典型入侵植物薇甘菊根际可培养固氮菌和氨化细菌的研究尚未见报道,这在很大程度上制约了我们对薇甘菊根际高效的氮素转化机制的深刻理解。【方法】采用传统平板涂布培养法对野外采集的薇甘菊根际土壤中的可培养固氮菌和氨化细菌进行了分离鉴定,并进行了接种验证实验。【结果】结果表明,入侵植物薇甘菊根际土壤中的固氮菌和氨化细菌的菌群密度显著高于两个本地伴生植物(火炭母和鸡屎藤),其固氮效率及有机氮矿化效率也优于2个本地种;系统发育分析表明：薇甘菊根际的固氮菌菌株归类于5个属,分别为伯克霍尔德氏菌属(Burkholderia)、肠杆菌属(Enterobacter)、植物杆菌属(Phytobacter)、新肠杆菌属(Kosakonia)和根瘤菌属(Rhizobium);氨化细菌归类于7个属,分别为沙雷氏菌属(Serratia)、不动杆菌属(Acinetobacter)、假单胞菌属(Pseudomonas)、博德特氏菌属(Bordetella)、寡养单胞菌属(Stenotrophomonas)、苍...     

落地生根内生固氮菌多样性和促生特性

【背景】内生固氮菌可以定殖于植物体内为植物提供营养物质,还能通过代谢促进植物生长,目前对于落地生根内生菌的研究鲜见报道。【目的】研究落地生根中内生固氮菌多样性。【方法】从表面消毒的植物组织中分离纯化内生菌,并通过乙炔还原法测定菌株的固氮酶活性。采用SDS-PAGE全细胞蛋白电泳和IS指纹图谱对菌株聚类,各类群代表菌株进行16S rRNA基因系统发育分析和生理生化鉴定。测定菌株固氮、分泌生长素和ACC脱氨酶、产铁载体、溶磷和解钾等促生特性。【结果】从落地生根中分离纯化出26株内生固氮菌,聚为5个类群,隶属于4个属的5个菌种,且各类群代表菌株具有多种促生功能。【结论】从落地生根中分离获得的内生菌具有丰富的遗传多样性和促生特性,并且存在新的微生物资源,有待开发利用。     

一株海洋放线菌的鉴定及其促生作用机理

【背景】海洋放线菌BM-2是本实验室从连云港海域分离得到的一株具有抗菌和促生作用的优良菌株,具有良好的开发应用前景。【目的】明确海洋放线菌BM-2的分类地位,揭示该菌株的促生作用机理,为菌株的开发应用提供理论依据。【方法】通过形态观察、生理生化特性和16S rRNA基因序列分析,对海洋放线菌BM-2菌株进行种属鉴定;采用透明圈法、平板划线法测定BM-2菌株解磷、解钾作用、固氮作用和产植酸酶、1-氨基环丙烷-1-羧基(1-aminocyclopropane-1-carboxylate,ACC)脱氨酶的能力;运用沙尔科夫斯基反应(Salkowski法)和铬天青(chromeazurol S,CAS)法分别测定菌株产吲哚乙酸(indole acetic acid,IAA)和产铁载体的能力。【结果】培养特征、菌落形态观察及生理生化试验结果表明,BM-2菌株符合链霉菌属(Streptomyces)的特征,16SrRNA基因序列与GenBank中栗褐链霉菌(Streptomycesbadius)的序列相似性为99.72%;BM-2菌株具有固氮和解有机磷活性,能够产生ACC脱氨酶、铁载体和IAA。【...     

4株茶树根际促生菌菌株的鉴定及促生作用

【背景】根际促生菌可以促进植物生长、提高植物抗性。茶树根际具有特殊的根土微生物生境,可以获得具促生作用的有益微生物。【目的】探究4株茶树根际促生菌菌株的分类地位及促生作用,筛选优良的根际促生菌菌株。【方法】通过形态、生理生化特征、16S rRNA基因序列同源性比对鉴定4株茶树根际促生菌,采用钼锑抗比色法测定溶磷量,通过比色法测定ACC脱氨酶活性、CAS法测定产铁载体能力、Salkowski法测定产IAA (Indoleacetic acid)的能力进行促生作用研究,通过盆栽实验测试白菜、空心菜、苋菜及水稻的株高及鲜重以分析促生效应。【结果】鉴定KKS-6-N1为放射型土壤杆菌(Agrobacteriumradiobacter), KKS-7-N7为铜绿假单胞菌(Pseudomonas aeruginosa),GD3为Pseudomonashunanensis,GD12为弯曲芽孢杆菌(Bacillusflexus)。固氮菌株KKS-6-N1可产铁载体;固氮菌株KKS-7-N7具有解磷及产铁载体能力,分泌的IAA含量高达101.29mg/L;解钾菌株GD3具溶磷能力,分泌的ACC脱氨酶酶活为8.09μmol/(mg·h),相对铁载体含量为0.31;具固氮解钾性能的菌株GD12分泌的ACC脱氨酶活性为14.46μmol/(mg·h)。盆栽试验表明,4个菌株对白菜、空心菜、苋菜的株高和鲜重均有明显促进作用,尤以GD3效果更甚。【结论】茶树根际促生菌菌株Pseudomonas hunanensis GD3促生作用显著,具有开发成微生物菌肥的潜力。     

岑溪药用野生稻高效内生固氮菌分离及促生特性

【目的】以广西岑溪市野生稻保护区的药用野生稻为材料,分离纯化内生细菌,筛选固氮酶活性较高和对作物促生效果较好的菌株。【方法】利用乙炔还原法检测固氮酶活性,采用SDS-PAGE全细胞蛋白电泳和IS-PCR指纹图谱技术对分离到的固氮菌进行聚类。利用16S rRNA基因和nifH基因确定其系统发育地位。采用钼锑抗比色法、Salkowski比色法和CAS检测法分别测定菌株溶磷性、生长素的分泌能力和产铁载体能力。通过平板和盆栽试验检测其对水稻的促生作用。【结果】共分离得到35株内生固氮菌,分为6个类群。其中CX24固氮酶活性最高,经鉴定属于Klebsiella variicola,其固氮酶活性为298.64 μmol/(L·h),为参比模式菌株DSM15968的9倍。另外该菌株还具有较高的溶磷性、分泌生长素和产铁载体能力,能够有效地促进水稻的萌发和生长。【结论】菌株CX24属于Klebsiella variicola,是一株高效内生固氮菌,具有很好的生产应用前景。     

耐镉促生菌株的分离鉴定及对大豆的促生效应

【背景】华南地区镉（Cd）污染严重,与有益微生物共生能够使作物通过直接或间接的机制解除镉毒,提高抗逆性,进而促进生长。耐镉促生菌剂具有广泛的应用前景。【目的】从华南地区受镉污染植株的根内和根际筛选出耐镉且能促进大豆生长的促生菌,以丰富促进田间大豆生产的优异菌种资源。【方法】采用平板划线法从植株的根内或根际分离菌株,通过生理生化特性和16S rRNA基因序列分析对分离菌株进行初步研究,利用盆栽试验探究镉胁迫下菌株对大豆生长的影响,通过测定丙二醛含量和总抗氧化能力探究菌株的耐镉机制。【结果】分离获得4株菌D1、D2、D3和D4,促生特性试验证明4株菌均具有溶磷、产吲哚乙酸和铁载体的能力。经16S rRNA基因序列分析鉴定,D1、D2、D3和D4菌株分别属于不动杆菌属、微小杆菌属、类芽孢杆菌属和普罗威登斯菌属。用这4株菌进行不同镉处理的大豆（巴西10号）盆栽试验,结果表明,4株菌均具有耐镉和促进大豆生长的作用。不添加镉的条件下,大豆接种D4菌株的地上部干重、根部干重和株高分别增加了28%、35%和31%;在添加20mg/kg-CdCl₂·5/2H₂...     

番茄内生菌的分离鉴定及菌株FQ-G3抗病促生特性

由灰葡萄孢(Botrytis cinerea)引起的灰霉病是番茄生产中最重要的病害之一,当前使用的杀菌剂因药物残留、病原菌抗药性及食品安全等原因逐渐受到限制。因此,利用拮抗微生物的生物防治逐渐成为灰霉病防控的有效策略。【目的】从番茄植株体内筛选具有抗病促生特性内生菌株并对其生防潜力进行评估,为开发番茄灰霉病生物防治新策略提供理论依据。【方法】采用组织分离法在番茄植株不同部位分离出内生细菌、真菌,结合16SrRNA和ITS序列分析,对候选菌株进行初步鉴定;通过菌株对峙培养、果实离体接种筛选对灰葡萄孢具有拮抗活性的内生菌;进一步测定菌株分泌生长素、嗜铁素的能力及其对拟南芥和番茄幼苗生长的促生特性。【结果】从番茄植株不同部位共分离出72株内生细菌和31株内生真菌,通过平板对峙法筛选出1株对多种病原菌具有较好抑菌活性的内生细菌FQ-G3,分子鉴定为Bacillus velezensis。FQ-G3对灰葡萄孢抑菌率达80.93%,并显著抑制灰葡萄孢在番茄果实上的扩展。该菌株能够分泌生长素、蛋白酶和嗜铁素,且对拟南芥、番茄幼苗具有明显的促生效果。【结论】本研究表明分离自番茄植株的内生菌FQ-G3具...     

两株具促生作用的苜蓿内生菌的分离纯化与鉴定

【目的】分离具有植物促生功能的苜蓿内生菌。【方法】从苜蓿的新鲜组织中分离纯化菌株,进行16S r RNA基因序列分析,生理生化鉴定并检测内生菌对苜蓿的促生特性。【结果】获得两株苜蓿内生菌,成团泛菌ASR16和短小芽孢杆菌ALR33。两株菌株均能产生植物生长激素IAA和嗜铁素,能溶解磷,对苜蓿的促生作用明显。【结论】获得两株具有植物促生特性的苜蓿内生菌ASR16和ALR33,可作为微生物菌肥的研究基础。     

ACC脱氨酶活性菌株ACC 30的分离、 鉴定及其促生作用

【目的】筛选具有1-氨基环丙烷-1-羧酸(简称ACC)脱氨酶活性的菌株,并探索该类菌的促生作用,有助于研发微生物肥料,实现农业增产。【方法】以ACC为唯一氮源,从土壤中富集和分离ACC脱氨酶产生菌;测定ACC脱氨酶的比活力,对酶活性最强的菌株根据形态和培养特征、生理生化特征及16S rDNA序列进行分类鉴定;分别采用菌液培养接种法与菌液浸种接种法初步研究该菌株对紫花苜蓿幼苗生长的促生作用。【结果】筛选得到6株ACC脱氨酶阳性细菌,其中菌株ACC 30酶活性最高,为0.217 U/mg,根据培养特征观察和生理生化指标测定结果,结合16S rDNA序列比对分析,确定ACC 30为产气肠杆菌(Enterobacter aerogenes)。促生试验表明,ACC 30可促进紫花苜蓿幼苗根伸长,菌液培养接种法与菌液浸种接种法两种处理方法下ACC 30分别使幼苗根相对伸长135%、136%,促生作用均明显且基本一致。但是,两种方法处理下ACC 30均抑制幼苗下胚轴伸长。【结论】筛选获得ACC脱氨酶活性菌株ACC 30,其酶活性较高且促生作用明显,有望进一步研发成为微生物肥料。     

Study of mechanisms for plant growth promotion elicited by rhizobacteria in Arabidopsis thaliana

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots and exert beneficial effects on plant health and development. We are investigating the mechanisms by which PGPR elicit plant growth promotion from the viewpoint of signal transduction pathways within plants. We report here our first study to determine if well-characterized PGPR strains, which previously demonstrated growth promotion of various other plants, also enhance plant growth in Arabidopsis thaliana. Eight different PGPR strains, including Bacillus subtilis GB03, B. amyloliquefaciens IN937a, B. pumilus SE-34, B. pumilus T4, B. pasteurii C9, Paenibacillus polymyxa E681, Pseudomonas fluorescens 89B-61, and Serratia marcescens 90-166, were evaluated for elicitation of growth promotion of wild-type and mutant Arabidopsis in vitro and in vivo. In vitro testing on MS medium indicated that all eight PGPR strains increased foliar fresh weight of Arabidopsis at distances of 2, 4, and 6 cm from the site of bacterial inoculation. Among the eight strains, IN937a and GB03 inhibited growth of Arabidopsis plants when the bacteria were inoculated 2 cm from the plants, while they significantly increased plant growth when inoculated 6 cm from the plants, suggesting that a bacterial metabolite that diffused into the agar accounted for growth promotion with this strain. In vivo, eight PGPR strains promoted foliar fresh weight under greenhouse conditions 4 weeks after sowing. To define signal transduction pathways associated with growth promotion elicited by PGPR, various plant-hormone mutants of Arabidopsis were evaluated in vitro and in vivo. Elicitation of growth promotion by PGPR strains in vitro involved signaling of brassinosteroid, IAA, salicylic acid, and gibberellins. In vivo testing indicated that ethylene signaling was involved in growth promotion. Results suggest that elicitation of growth promotion by PGPR in Arabidopsis is associated with several different signal transduction pathways and that such signaling may be different for plants grown in vitro vs. in vivo.     

Influence of aromatic hydrocarbons on growth,plant growth promoting activities and survival in soil of Azotobacter chroococcum strain JL104

This study was undertaken to determine the effect of aromatic hydrocarbons on growth and plant growth promoting activities of Azotobacter chroococcum strain JL104. The organism was grown on Jensen’s media without sucrose, supplemented with different concentrations of aromatic hydrocarbons. Azotobacter chroococcum strain JL104 was able to grow in the presence of benzene, toluene, aniline and benzoic acid and was able to utilize these as sole carbon source as well. The culture showed the highest growth in presence of 0.5% concentrations of aniline and benzoic acid and 0.01% concentrations of benzene and toluene. Maximum indole acetic acid (IAA) production and acetylene reduction activity (ARA) were recorded with benzene and benzoic acid, respectively. Among other substituted benzene derivatives such as xylene, p-hydroxybenzoic acid, di-nitrophenol and di-chlorophenol, xylene was observed to be the least toxic and di-nitrophenol the most toxic hydrocarbon. The highest soil survival was found in soil amended with 1% sucrose however, the population of A. chroococccum strain JL104 declined continuously in unamended soil. Amongst various hydrocarbons, 0.1% toluene amended soil supported the maximum survival, indicating it to be least toxic aromatic hydrocarbon carbon in soil.     

广西葛根内生细菌的分离鉴定及其促生特性

【背景】植物内生菌长期与宿主共生,对宿主生长发育产生影响。葛根作为重要的药食两用作物,葛根内生菌的研究具有重要实践意义。【目的】对广西葛根根部内生细菌进行分离、鉴定及促植物生长特性分析,旨在了解该药食同源植物内生细菌种群结构及其促生特性,为分析内生菌群体在药食同源植物产量和品质形成的作用及其内生细菌资源的开发利用提供参考。【方法】采用6种不同的培养基从广西葛根的根瘤、根系和根愈伤组织分离内生细菌,16S rRNA基因测序和系统发育分析内生细菌的分布特征和遗传多样性,采用生理生化方法测定分离菌株的固氮活性、溶磷特性、产生嗜铁素、分泌吲哚乙酸(indole-3-aceticacid,IAA)等促生特性。【结果】从葛根根瘤、根系和根部愈伤组织中共分离得到223个菌株,16S rRNA基因测序鉴定这些菌株隶属于2门4纲10科19属,其中芽孢杆菌属、假单胞菌属、土壤杆菌属、肠杆菌属为葛根优势菌群;内生细菌数量和群落组成存在明显的组织特异性,其数量表现为根瘤>根系>根愈伤组织,但其种群多样性表现为根愈伤组织>根系>根瘤。不同培养基分离出的细菌种群丰富度有差异。从供试菌株中筛...     

南海东海岛近海固氮细菌多样性及对菜心的促生作用

海洋固氮细菌在自然界氮循环中发挥着重要作用,筛选和开发海洋固氮促生的菌种资源,对于生物菌肥的开发应用和农业生产具有重要意义。[目的]研究海洋固氮细菌的生物多样性及对陆地作物的促生作用,筛选优良的植物根际促生菌株。[方法]通过形态特征、生理生化试验和16S rRNA基因序列比对进行菌属鉴定;将解磷、解钾、产蛋白酶和纤维素酶等性能优良的菌株作为菜心盆栽试验的组合菌液,探究对菜心能否起促生作用。[结果]本研究从南海东海岛的海岛沉积物中筛选出18株固氮菌,分布在6个属9种,不动杆菌属4株,假交替单胞菌属1株,芽孢杆菌属8株,嗜冷杆菌属1株,海单胞菌属1株,交替单胞菌属3株。菜心幼苗经过组合菌剂的浇灌,在茎高、茎粗、最大叶宽和最大叶长4个指标均表明对菜心有显著的促生作用。其中,以芽孢杆菌属和不动杆菌属的菌株在菜心的生长过程中起关键的促进作用,对菜心的促生性能最佳。[结论]南海近海具有种类丰富多样的固氮细菌,以芽孢杆菌属和不动杆菌属的菌株促生作用最为显著,具有开发成微生物菌肥的潜力,为优良的海洋促生微生物菌种资源的定向利用及蔬菜的无公害生产提供重要依据。     

番茄青枯病拮抗菌的定向筛选及其抗病促生机制研究

[目的] 从抑病型番茄根际土壤中筛选青枯病的高效拮抗促生菌,阐明其防病促生机制。[方法] 以番茄青枯雷尔氏菌（Ralstonia solanacearum）为靶病原菌,采用平板抑菌圈法,筛选拮抗菌;通过BOX-PCR指纹图谱鉴定菌株多样性,以平板透明圈法评价其产酶活性,并针对抑菌能力强、产酶种类多的拮抗菌开展16S rRNA基因系统发育分析;通过温室试验评价拮抗菌的防病促生能力,并在此基础上通过实时荧光定量PCR研究生防细菌对番茄青枯病的防病促生机制。[结果] 从番茄根际土壤分离获得29株细菌,其中15株对青枯菌具有拮抗功能,进一步通过BOX-PCR指纹图谱、酶活分析获得4株具有潜在防治番茄青枯病、促进生长的功能菌（B2、B5、B20、B23）,通过16S rRNA系统发育分析鉴定B2拮抗菌为解淀粉芽孢杆菌（Bacillus amyloliquefaciens）,B5和B20拮抗菌为枯草芽孢杆菌（Bacillus subtilis）,B23拮抗菌为贝莱斯芽孢杆菌（Bacillus velezensis）;温室试验表明,B2、B5、B20、B23拮抗菌的抑病效果分别为35.59%、8.47%、32.20%、96.61%,并且均能显著增加番茄生物量和生理性状,如地上部鲜重、总叶绿素含量、地下部根尖数等。B2、B5、B23拮抗菌显著促进番茄株高和根长,B2、B20、B23拮抗菌显著增加茎粗;而B23拮抗菌显著增加根系分叉数;实时荧光定量分析表明,B2、B20、B23拮抗菌株可促进抗病相关功能基因PR1α、POD1的表达量,B2、B5、B23拮抗菌促进吲哚乙酸（IAA）信号通路应答关键基因ctd1的表达量,B2、B5、B20、B23拮抗菌均降低乙烯（ETH）信号通路应答关键基因ERF2的表达量。[结论] 本研究分离筛选获得4株对番茄青枯病具有显著防治效果以及促进番茄生长的PGPR菌株,可为定向筛选植物促生防病菌提供理论依据。     

一株具有防病促生功能的贝莱斯芽孢杆菌SF327

【目的】筛选植物根际促生贝莱斯芽孢杆菌,分析菌株的生防潜力和全基因组特征。【方法】通过温室小青菜促生试验以及植物益生表型的分析,明确具有促生功能的菌株SF327。用滤纸片法测定菌株SF327对5种植物病原真菌以及4种植物病原细菌的拮抗活性。通过大田喷雾接种的方式评价菌株SF327对水稻白叶枯病的防治潜力。利用antiSMASH分析预测菌株SF327产生的二次代谢产物。通过比较基因组分析SF327与2株植物根际益生贝莱斯芽孢杆菌的代表性菌株FZB42和SQR9的亲缘关系、核心基因以及二次代谢产物合成基因簇。【结果】菌株SF327能够产生生长素吲哚-3-乙酸,是一株有益的根围促生菌;对稻瘟病菌、黄瓜枯萎病菌、辣椒疫霉菌、橡胶树胶孢炭疽菌、尖孢炭疽病菌都具有明显的拮抗作用;也具有防治水稻白叶枯病的生防潜力。菌株SF327基因组全长4.08 Mb,GC含量为46.49%,共编码4 033个基因,含有13个潜在的次生代谢产物编码基因簇,不含有质粒。SF327与FZB42和SQR9具有较近的亲缘关系,有87%以上的核心基因相同,但与SQR9的亲缘关系较近。【结论】B. velezensis SF327是一株具有宽广拮抗谱的多功能菌株,具有较好的生防应用潜力。     

一株连香树根际促生细菌LWK2的分离鉴定及其全基因组序列分析

【背景】植物根际促生细菌是一类位于植物根际并能对植物生长产生促进作用的有益菌,在微生物肥料领域具有重要的应用价值。【目的】对濒危植物连香树根际的植物根际促生细菌进行分离筛选和连香树接种效应评价,挑选对连香树生长促进作用最为显著的菌种进行促生特性分析、菌种鉴定及全基因组序列测定与促生相关基因分析。【方法】利用相应筛选培养基对连香树根际土壤中解有机磷、溶无机磷和解钾细菌进行分离筛选,通过根际接种验证各菌株对连香树实生苗的促生能力。从中选取促生作用最为显著的细菌,进行解钾能力、产吲哚乙酸(indole-3-acetic acid,IAA)和1-氨基环丙烷-1-羧酸(1-aminocyclopropane-1-carboxylate,ACC)脱氨酶能力测定。利用菌体形态观察、16S rRNA基因序列分析及全基因组序列的平均核苷酸一致性比对进行菌种鉴定。最后利用基因组功能注释和比较基因组学分析对该菌株中的植物促生及重金属抗性相关基因进行解析。【结果】从连香树根际土壤中共筛选得到3株解有机磷细菌、2株溶无机磷细菌和2株解钾细菌,其中解钾细菌LWK2对连香树实生苗的生长促进作用最为显著。该菌株能够产...     

Effects of inoculation with plant growth promoting rhizobacteria (PGPRs) andSinorhizobium fredii on biological nitrogen fixation, nodulation and growth ofGlycine max cv. Osumi

We investigated the effects of three plant growth promoting rhizobacteria (PGPR), on Biological Nitrogen Fixation (BNF), nodulation and growth promotion by soybean (Glycine max) var. Osumi plants. The strains, Aur 6, Aur 9 and Cell 4, belong toPsedomonas fluorescens, Chryseobacterium balustinum andSerratia fonticola, respectively. Inoculation modes for the PGPRs andSinorhizobium fredii (carried out through irrigation), were examined. In the first mode, PGPRs andS. fredii were co-inoculated. In the second mode, we first inoculatedS. fredii and after the PGPRs, which were added 5 or 10 days later (each inoculation being an independent treatment). In the third mode, the PGPRs were inoculated first, and theS. fredii was inoculated 5 days later. We also included treatments inoculated with only the PGPRs (one PGPR per treatment) and only withS. fredii. Plants were maintained in a greenhouse under controlled environmental conditions, and were sampled 3 months after sowing. The results obtained showed the effects of the inoculation sequence. The most significant effects on growth parameters (stem plus leaf weight and fresh root weight) were found when inoculations with PGPR andS. fredii were at different times or when we inoculated only with PGPR and the plants were watered with nitrogen. Co-inoculation had no positive effects on any parameter, probably due to competition between the PGPR andS. fredii. Our results indicate that the inoculation modes with PGPR and rhizobia play a very important role in the effects produced. Thus, although plant growth promoting rhizobacteria may interact synergistically with root-nodulating rhizobia, plant growth promoting rhizobacteria selected for one crop should be assessed for potentially hazardous effects on other crops before being used as inoculants.     

Characterization of a novel plant growth-promoting bacteria strain Delftia tsuruhatensis HR4 both as a diazotroph and a potential biocontrol agent against various plant pathogens

A novel, plant growth-promoting bacterium Delftia tsuruhatensis, strain HR4, was isolated from the rhizoplane of rice (Oryza sativa L., cv. Yueguang) in North China. In vitro antagonistic assay showed this strain could suppress the growth of various plant pathogens effectively, especially the three main rice pathogens (Xanthomonas oryzae pv. oryzae, Rhizoctonia solani and Pyricularia oryzae Cavara). Treated with strain HR4 culture, rice blast, rice bacterial blight and rice sheath blight for cv. Yuefu and cv. Nonghu 6 were evidently controlled in the greenhouse. Strain HR4 also showed a high nitrogen-fixing activity in N-free Döbereiner culture medium. The acetylene reduction activity and ¹⁵N₂-fixing activity (N₂FA) were 13.06 C₂H₄ nmol ml⁻¹ h⁻¹ and 2.052 ¹⁵Na.e.%, respectively. The nif gene was located in the chromosome of this strain. Based on phenotypic, physiological, biochemical and phylogenetic studies, strain HR4 could be classified as a member of D. tsuruhatensis. However, comparisons of characteristics with other known species of the genus Delftia suggested that strain HR4 was a novel dizotrophic PGPB strain.