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。     

氢氧化细菌SDW-16的分离鉴定及促生特性

利用气体循环培养体系从沙打旺根际土壤分离得到1株氢氧化细菌SDW-16(GenBank登录号:KF835389),16S rDNA序列分析和生理生化特征鉴定其为荧光假单胞菌(Pseudomonas fluorescens)。菌株对植物促生机制的初步研究表明菌株SDW-16除具有铁载体分泌能力外,还具有产IAA和ACC脱氨酶活性,其中产IAA量为(21.62±0.30)μg/mL,ACC脱氨酶活力高达(8 372.17±805.43) nmol/(mg·h)。菌株SDW-16具有多项促生能力且均高于其他菌株,说明菌株SDW-16有较高的促生特性,同时也初步证明了氢氧化细菌的促生机制。     

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。     

三种蓝莓根际细菌的分离及其对蓝莓苗生长发育的影响

【目的】从3种蓝莓根际土壤中分离细菌,探究蓝莓根际土壤细菌多样性,并筛选具有产酸、促生长、抑菌性能的菌株,为蓝莓专用微生物肥料的研究提供优质菌株资源和理论基础。【方法】选用5种培养基分离3种蓝莓根际土壤细菌,并进行16S rRNA基因测序和系统发育分析。筛选产酸、产吲哚-3-乙酸（indole-3-acetic acid,IAA）和铁载体、固氮、溶磷和抑制灰葡萄孢生长的菌株,挑选最适菌株制备菌剂进行蓝莓苗盆栽实验验证促生能力,并检测菌剂对蓝莓元素吸收和根际土壤肥力的影响。【结果】从3种蓝莓根际土壤分离得到124株细菌,挑选70株代表性菌株进行16S rRNA基因测序,分布于3个门21个属,其中芽孢杆菌属（Bacillus）、假单胞菌属（Pseudomonas）、链霉菌属（Streptomyces）和红球菌属（Rhodococcus）为优势分离菌群。代表性菌株中,21.4%的菌株能产酸,21.4%的菌株产吲哚-3-乙酸,47.1%的菌株具有固氮潜力,65.7%的菌株具有解磷能力,14.3%的菌株能产铁载体。少量菌株同时具有产酸、产IAA、固氮、解磷和抑菌等能力。选取具有产酸和多种促生特征的菌株绿针假单胞菌CSM-70和双鱼假单胞菌CSM-129进行盆栽蓝莓苗处理,发现2株菌均能显著促进蓝莓苗的生长发育并调控根际土壤pH,其中菌株CSM-70处理还显著促进了蓝莓叶片氮、磷元素的吸收,提升了土壤速效钾、碱解氮的含量。【结论】蓝莓根际细菌多样性高且蕴藏着丰富的促生长菌株,绿针假单胞菌CSM-70和双鱼假单胞菌CSM-129能够促进蓝莓苗生长、调控根际土壤pH和肥力,并促进植株养分吸收,具有蓝莓专用微生物菌剂研制与应用的潜力。     

一株人参内生1-氨基环丙烷-1-1羧酸(ACC)脱氨酶活性细菌的筛选、鉴定及其对宿主生长的影响

【目的】从人参内生细菌中获得具有1-氨基环丙烷1-羧酸(ACC)脱氨酶活性的菌株,并进行促生效果的验证。【方法】结合初筛和复筛的方法筛选具有ACC脱氨酶活性的人参内生菌株;采用Ashby培养基和固氮酶基因验证其固氮潜能;菌碟法及钼锑抗比色法测定其解磷能力;CAS方法检测产生铁载体能力;通过室内及田间试验测定菌株对人参生长的促进作用。通过形态学、生理生化测定及16S rRNA序列分析明确菌株的分类地位。【结果】从120株人参内生菌中获得了一株具有较高ACC脱氨酶活性的菌株JJ8-3,其酶活性为α-酮丁酸6.7μmol/(mg·h);且具有解磷特性、固氮潜能和产生铁载体能力;能明显促进人参种子及根部的生长;经鉴定菌株JJ8-3为荧光假单胞菌(Pseudomonas fluorescens)。【结论】获得了一株具有ACC脱氨酶活性的人参内生细菌,将为其在促进植物生长中的应用和研究奠定基础。     

古尔班通古特沙漠苔藓结皮土壤中促生菌的分离筛选及促生特性研究

从古尔班通古特沙漠南缘苔藓结皮土壤中分离筛选植物促生菌并阐明其促生特性，对于发掘和应用功能性微生物制剂，促进植被恢复和提升荒漠固沙能力等具有积极意义。采用富集方法从苔藓生物结皮下0～20 cm土壤中分离可培养微生物。利用选择性培养基筛选具溶磷、产铁载体、分泌吲哚乙酸（IAA）特性的菌株。采用钼锑抗比色法、CAS检测法、Salkowski比色法分别测定菌株溶磷量、产生铁载体的浓度、分泌IAA的含量，并对性能优良的菌株进行分类鉴定。共筛选出促生菌31株，其中溶磷菌31株，产铁载体菌13株，分泌IAA菌28株。菌株LB5WH溶解无机磷能力最强，溶磷量为302.24 mg/L；菌株LB15产铁载体能力最强，产生铁载体的浓度 Su值（铁载体活性单位）为85.7%；菌株GA20分泌IAA活性最强，分泌量为15.46 mg/L。菌株LB5WH、LB15同时具有溶磷、产铁载体和分泌IAA活性，菌株GA20具有溶解有机磷、分泌IAA活性。菌株溶解无机磷能力要强于溶解有机磷能力，溶解无机磷菌株的溶磷量与培养液pH值之间呈显著负相关。经鉴定，菌株LB5WH属于芽胞杆菌属（Bacillus），菌株GA20属于寡养单胞菌属（Stenotrophomonas），菌株LB15属于赖氨酸芽胞杆菌属（Lysinibacillus）。这三株细菌的促生功能较多，具有进一步开发为微生物肥料的潜能。本研究为丰富荒漠区促生菌资源，进一步深入研究苔藓结皮下土壤-微生物-植物互作的生态调控机制及荒漠植物促生菌的促生机理提供菌种资源。     

烟草根际可培养微生物多样性及防病促生菌的筛选

[背景] 根际微生物在植物根部生态系统中扮演着重要角色,影响着植物的营养吸收和健康生长。[目的] 了解常年不发病烟田烤烟品种K326根际可培养微生物的多样性,筛选具有防病促生功能的菌株,为烟草病害绿色防控提供资源。[方法] 采用传统培养方法对烟草根际土壤中的细菌和真菌进行分离鉴定,评价菌株的促生特性及病原菌拮抗能力,并进一步验证典型菌株对盆栽烟苗的促生效果。[结果] 共获得261株微生物菌株,包括160株细菌和101株真菌。经分子鉴定,细菌中以变形菌门（Proteobacteria）和厚壁菌门（Firmicutes）为主要类群;真菌中以子囊菌门（Ascomycota）和毛霉菌门（Mucoromycota）为主要类群。在属水平上,细菌以假单胞菌属（Pseudomonas）和芽孢杆菌属（Bacillus）为主,真菌以曲霉属（Aspergillus）和青霉属（Penicillium）为主。从不同种水平上进一步选择44株细菌为代表菌株,发现它们均具有不同程度的吲哚-3-乙酸（Indole-3-Acetic Acid,IAA）产生能力,9株能够溶解有机磷,16株能够溶解无机磷,13株产生铁载体,14株产生生1-氨基环丙烷-1-羧酸（1-Aminocyclopropane-1-Carboxylate,ACC）脱氨酶。从160株细菌中筛选得到抑制青枯病菌和黑胫病菌的菌株数目分别为25、26株。经盆栽试验发现韩国假单胞菌（P. koreensis） HCH2-3、浅黄绿假单胞菌（P. lurida） FGD5-2和贝莱斯芽孢杆菌（B. velezensis） EM-1对烟苗呈现不同程度的促生作用,其中3株菌联合施加对烟苗的促生效果最明显。[结论] 烟草根际存在着丰富多样的具有防病促生潜力的微生物,并且合成菌群或功能互补的菌株联合施用是未来微生物菌剂研发的重要方向。     

贵州喀斯特地区具ACC脱氨酶活性细菌的分离和鉴定

1-氨基环丙烷-1-羧酸(ACC)脱氨酶能够降解乙烯前体,从而有助于植物生长。具有ACC脱氨酶活性细菌在旱胁迫下具有植物促生作用。本研究从贵州地区选取典型喀斯特地貌区域159份土壤样品中分离并鉴定出具有ACC脱氨酶活性的细菌188株。利用16S r DNA测序分析将这些菌株归为14属63种,优势菌属为假单胞菌属和伯克氏菌属,分别有ACC脱氨酶活性的细菌18种和17种。对63种菌株的ACC脱氨酶活性定量检测,酶活最高的菌株是AL30ADF120(Cupriavidus oxalaticus),为3.639 U/mg。据我们所知,这是第一个有关喀斯特地区土壤中的具有ACC脱氨酶活性细菌名录,为将来研究ACC脱氨酶活性细菌的植物促生作用奠定了基础。     

假单胞菌T1-3-2的抑菌特性及其对杉木的抗病促生作用

【背景】生物防治是“基于自然的解决方案”,有利于生态文明和可持续发展,开展生物防治技术研究的基础是明确菌株的生防作用和抑菌特性。【目的】探究杉木内生菌株T1-3-2的抑菌促生特性,为研制该菌株生防菌剂、防治杉木炭疽病(Cunninghamia lanceolata anthracnose)奠定基础。【方法】通过形态学特征、生理生化特性及16S rRNA基因序列分析,确定菌株T1-3-2的分类地位;通过平板对峙、菌落径向生长抑制率和平板倒扣等方法测定细菌及其挥发性气体和次级代谢产物的抑菌作用;同时,测定其促生作用和室内防效。【结果】菌株T1-3-2与桉生假单胞菌(Pseudomonas eucalypticola)亲缘性较近,属于假单胞菌属。该菌株对分属于6个属的10株靶标菌株具有较强的拮抗作用,尤其对炭疽菌属、拟盘多毛孢属、黑孢霉属和葡萄座腔菌属的6株靶标菌株抑制率高达80%以上。室内盆栽试验显示：菌株T1-3-2用Kings Medium B液体培养基的发酵菌液对杉木炭疽病的防效可达74.20%,同时能有效改善杉木幼苗的生长状况、增加生物量。【结论】菌株T1-3-2隶属于假单胞菌属,对杉木具有良好的抗病促生作用,是一株具有开发潜力的生防菌株。     

缓解花生连作障碍的根际促生菌分离及功能鉴定

[目的] 长期连作障碍严重降低花生生产的产量及品质,根际促生菌可有效降解土壤中自毒化感物质、抑制植物病原菌生长及促进植物生长,从而有效缓解连作障碍问题。筛选优化具有缓解花生连作障碍能力的多功能根际益生微生物,验证其益生作用能力,为根际促生菌株在连作障碍中的应用提供理论依据及技术支持。[方法] 采集连作12年地块花生根际土壤,利用以酚酸为唯一碳源的筛选培养基获得具有酚酸自毒化感物质降解及利用能力的根际促生菌,通过16S rRNA基因测序进行系统发育分析,确定根际促生菌菌株的分类地位,并验证其对植物病原菌生长抑制能力及解磷、解钾、产植物激素吲哚乙酸能力。[结果] 从连作12年的花生发病土壤中获得7株可高效降解酚酸类自毒物质且降解底物多样的根际微生物菌株,经16S rRNA测序比对分别为克雷伯氏菌B02 （Klebsiella sp.B02）、克雷伯氏菌B07 （Klebsiella sp.B07）、克雷伯氏菌B15 （Klebsiella sp.B15）、芽孢杆菌B28 （Bacillus sp.B28）、不动杆菌P09 （Acinetobacter sp.P09）、布鲁氏杆菌VA05 （Brucella sp.VA05）、芽孢杆菌CA04 （Bacillus sp.CA04）。促生实验表明,7株高效降解菌株均可以合成吲哚乙酸,3株具有固氮能力,4株菌具有解有机磷及无机磷的能力,2株菌具有解钾的能力。拮抗实验表明,2株菌可以抑制多种植物病原菌的生长,均为芽孢杆菌属。选取Bacillus sp.B28初步验证对花生种子萌发及幼苗生长的影响,结果表明根际促生菌可显著缓解酚酸对花生种子发芽的抑制,并明显促进花生幼苗的生长。[结论] 获得多株具有降解酚酸类自毒化感物质、抑制植物病原菌生长及促进植物生长的多功能花生根际促生菌,更好地为根际促生菌在连作障碍治理中的有效应用提供菌株及技术支持。     

Characterization of plant-growth promoting diazotrophic bacteria isolated from field grown Chinese cabbage under different fertilization conditions

Diazotrophic bacteria isolated from the rhizosphere of Chinese cabbage were assessed for other plant growth promoting characteristics viz., production of IAA, ethylene, ACC deaminase, phosphate solubilization, and gnotobiotic root elongation. Their effect on inoculation to Chinese cabbage was also observed under growth chamber conditions. A total of 19 strains that showed higher nitrogenase activity identified by 16S rRNA gene sequence analysis were found to be the members of the genera Pseudomonas and Agrobacterium belonging to α- and γ-Proteobacteria groups. These strains were also efficient in producing IAA and ACC deaminase though they produced low levels of ethylene and no phosphate solubilization. In addition, inoculation of selected diazotrophic bacterial strains significantly increased seedling length, dry weight, and total nitrogen when compared to uninoculated control. The colonization of crop plants by diazotrophic bacteria can be affected by many biotic and abiotic factors, and further studies are oriented towards investigating the factors that could influence the establishment of a selected bacterial community.     

具ACC脱氨酶活性大豆根瘤内生菌的筛选、抗性及促生作用北大核心CSCD

【目的】从大豆根瘤中筛选具ACC(1-氨基环丙烷-1-羧基)脱氨酶活性的内生细菌,对活性菌株的抗盐碱性、系统分类地位以及代表菌株的促生长作用进行研究,为发掘和应用抗逆、促生优良菌种资源提供理论基础。【方法】以ACC作为唯一氮源测定菌株产ACC脱氨酶特性,采用标准曲线法测定α-丁酮酸含量,比色法定量测定ACC脱氨酶活力,固体平板筛选法对活性菌株进行抗性分析,通过菌体形态及生理生化特性测定、16S rRNA基因序列同源性分析鉴定菌株分类地位,采用盆栽试验验证代表菌株的促生作用。【结果】从河南省13个市(地区)36个点采集的大豆根瘤中筛选出8株ACC脱氨酶内生细菌,其中菌株DD132的酶活性最高(15.712 U/mg)。筛选菌株可耐受4%–6%NaCl,其中菌株DD165、DD132可耐受9%NaCl盐浓度。在pH 11时5株(DD14、DD132、DD67、DD141、DD131)生长良好,说明这些菌株有较强耐碱性。8株产ACC脱氨酶菌株分属于4属,即芽孢杆菌属(Bacillus)、肠杆菌属(Enterobacter)、寡养单胞菌属(Stenotrophomonas)和泛菌属(Pantoea)。接种试验表明内生菌DD132对小麦幼苗生长具有明显促生长作用。【结论】大豆根瘤内具ACC脱氨酶高活性菌株有较强耐盐碱性,其中菌株DD132对小麦幼苗生长有明显促生长作用。为发掘和应用抗逆、促生的优良菌种资源提供理论基础。     

Regulation of ethylene levels in canola (Brassica campestris) by 1-aminocyclopropane-1-carboxylate deaminase-containing Methylobacterium fujisawaense

We report the presence of ACC deaminase in Methylobacterium fujisawaense and its lowering of ethylene levels and promotion of root elongation in canola seedlings under gnotobiotic conditions. To test a part of the previous model proposed for ACC deaminase producing bacteria with Methylobacterium, ACC levels and various enzyme activities were monitored in canola. Lower amounts of ACC were present in the tissues of seeds treated with M. fujisawaense strains than in control seeds treated with MgSO₄. Though the increased activities of ACC synthase in the tissue extracts of the treated seedlings might be due to bacterial indole-3-acetic acid, the amount of ACC was reduced due to bacterial ACC deaminase activity. The activities of ACC oxidase, the enzyme catalyzing conversion of ACC to ethylene remained lower in M. fujisawaense treated seedlings. This consequently lowered the ethylene in plants and prevented ethylene inhibition of root elongation. Our results collectively suggest that Methylobacterium commonly found in soils, as well as on the surfaces of leaves, seeds, and in the rhizosphere of a wide variety of plants could be better exploited to promote plant growth.     

滨海盐渍土野大豆根瘤菌分离筛选及其在大豆中的应用

【目的】了解盐渍土野大豆根瘤菌的多样性，筛选具有耐盐促生作用的菌株，为栽培大豆耐盐菌剂的开发提供菌种资源。【方法】采用传统培养方法从滨海盐渍土野大豆中分离根瘤菌，评价菌株的促生特性，并验证其对野大豆和栽培大豆的促生效果。【结果】从野大豆根和根瘤样品中分离出87株根瘤菌，主要为中华根瘤菌属(Sinorhizobium)、根瘤菌属(Rhizobium)和慢生根瘤菌属(Bradyrhizobium)。测定了24株代表性菌株的促生特性，发现有16株根瘤菌具有产吲哚-3-乙酸(indole-3-acetic acid, IAA)能力，6株能够产生1-氨基环丙烷-1-羧酸(1-amino-cyclopropane-1- carboxylic, ACC)脱氨酶，16株具有溶磷活性，6株能够产生铁载体。根据以上促生特性，选择了11株优良根瘤菌进行野大豆促生和结瘤能力评价，发现美洲中华根瘤菌(Sinorhizobium americanus) DL3的性能优于其他菌株。最后，通过盆栽试验检测了菌株DL3对野大豆和栽培大豆耐盐能力的影响，发现菌株DL3在盐胁迫下能促进野大豆和大豆的生长，同时，降低了叶片脯氨酸水平，缓解了植物的盐胁迫程度。【结论】菌株DL3在提高植物耐盐性方面具有一定的作用，对实现大豆的盐碱地种植具有重要的理论意义和实践价值。     

Isolation of ACC deaminase producing PGPR from rice rhizosphere and evaluating their plant growth promoting activity under salt stress

Aims

Bacteria possessing ACC deaminase activity reduce the level of stress ethylene conferring resistance and stimulating growth of plants under various biotic and abiotic stresses. The present study aims at isolating efficient ACC deaminase producing PGPR strains from the rhizosphere of rice plants grown in coastal saline soils and quantifying the effect of potent PGPR isolates on rice seed germination and seedling growth under salinity stress and ethylene production from rice seedlings inoculated with ACC deaminase containing PGPR.

Methods

Soils from root region of rice growing in coastal soils of varying salinity were used for isolating ACC deaminase producing bacteria and three bacterial isolates were identified following polyphasic taxonomy. Seed germination, root growth and stress ethylene production in rice seedlings following inoculation with selected PGPR under salt stress were quantified.

Results

Inoculation with selected PGPR isolates had considerable positive impacts on different growth parameters of rice including germination percentage, shoot and root growth and chlorophyll content as compared to uninoculated control. Inoculation with the ACC deaminase producing strains reduced ethylene production under salinity stress.

Conclusions

This study demonstrates the effectiveness of rhizobacteria containing ACC deaminase for enhancing salt tolerance and consequently improving the growth of rice plants under salt-stress conditions.     

1-Aminocyclopropane-1-Carboxylate (ACC) Deaminase Genes in Rhizobia from Southern Saskatchewan

A collection of 233 rhizobia strains from 30 different sites across Saskatchewan, Canada was assayed for 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, with 27 of the strains displaying activity. When all 27 strains were characterized based on 16S rRNA gene sequences, it was noted that 26 strains are close to Rhizobium leguminosarum and one strain is close to Rhizobium gallicum. Polymerase chain reaction (PCR) was used to rapidly isolate ACC deaminase structural genes from the above-mentioned 27 strains; 17 of them have 99% identities with the previously characterized ACC deaminase structural gene (acdS) from R. leguminosarum bv. viciae 128C53K, whereas the other ten strains are 84% identical (864~866/1,020 bp) compared to the acdS from strain 128C53K. Southern hybridization showed that each strain has only one ACC deaminase gene. Using inverse PCR, the region upstream of the ACC deaminase structural genes was characterized for all 27 strains, and 17 of these strains were shown to encode a leucine-responsive regulatory protein. The results are discussed in the context of a previously proposed model for the regulation of bacterial ACC deaminase in R. leguminosarum 128C53K. An erratum to this article can be found at     

Mesorhizobium ciceri LMS-1 expressing an exogenous 1-aminocyclopropane-1-carboxylate (ACC) deaminase increases its nodulation abilities and chickpea plant resistance to soil constraints

Aims: Our goal was to understand the symbiotic behaviour of a Mesorhizobium strain expressing an exogenous 1‐aminocyclopropane‐1‐carboxylate (ACC) deaminase, which was used as an inoculant of chickpea (Cicer arietinum) plants growing in soil. Methods and Results: Mesorhizobium ciceri LMS‐1 (pRKACC) was tested for its plant growth promotion abilities on two chickpea cultivars (ELMO and CHK3226) growing in nonsterilized soil that displayed biotic and abiotic constraints to plant growth. When compared to its wild‐type form, the M. ciceri LMS‐1 (pRKACC) strain showed an increased nodulation performance of c. 125 and 180% and increased nodule weight of c. 45 and 147% in chickpea cultivars ELMO and CHK3226, respectively. Mesorhizobium ciceri LMS‐1 (pRKACC) was also able to augment the total biomass of both chickpea plant cultivars by c. 45% and to reduce chickpea root rot disease susceptibility. Conclusions: The results obtained indicate that the production of ACC deaminase under free living conditions by Mesorhizobium strains increases the nodulation, plant growth abilities and biocontrol potential of these strains. Significance and Impact of the Study: This is the first study regarding the use of a transformed rhizobial strain expressing an exogenous ACC deaminase in different plant cultivars growing in soil. Hence, obtaining Mesorhizobium strains with high ACC deaminase activity is a matter of extreme importance for the development of inoculants for field applications.     

Selection of ACC deaminase positive,thermohalotolerant and drought tolerance enhancing plant growth-promoting bacteria from rhizospheres of Cyamopsis tetragonoloba grown in arid regions

Plant growth-promoting bacteria (PGPB) expressing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity are widely acknowledged to have a role in mitigation of abiotic stress caused by extreme environmental conditions. Consequently, several studies have focused on the isolation of ACC deaminase positive PGPBs. However, the application of such strains in drought-prone arid regions has remained grossly under-exploited. In order to be used in arid agroecosystems, PGPBs need to have the dual capability: to express ACC deaminase and to have the ability to tolerate increased temperature and salt concentration. Conspicuously, to date, very few studies have reported about isolation and characterization of PGPBs with this kind of dual capability. Here we report the isolation of bacterial strains from rhizosphere(s) of Cyamopsis tetragonoloba, a commercial crop from arid regions of Rajasthan, India, and their characterization for ACC deaminase activity and thermohalotolerance. Isolates found positive for desired traits were subsequently assessed for plant growth promotion under simulated drought conditions. Our finding showed that although the bacterial diversity within the rhizosphere of C. tetragonoloba grown in the arid region is quite poor, multiple isolates are ACC deaminase positive. Four isolates were found to be ACC deaminase positive, thermohalotolerant, and successfully enhanced drought tolerance. These isolates were identified as strains belonging to genera Pseudomonas, Enterobacter, and Stenotrophomonas based on 16S rRNA sequence homology.     

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...     

Isolation of ACC deaminase-producing habitat-adapted symbiotic bacteria associated with halophyte Limonium sinense (Girard) Kuntze and evaluating their plant growth-promoting activity under salt stress

Background and aims

Many plant growth-promoting endophytes (PGPE) possessing 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity can reduce the level of stress ethylene and assist their host plants cope with various biotic and abiotic stresses. However, information about the endophytic bacteria colonizing in the coastal halophytes is still very scarce. This study aims at isolating efficient ACC deaminase-producing plant growth-promoting (PGP) bacterial strains from the inner tissues of a traditional Chinese folk medicine Limonium sinense (Girard) Kuntze, a halophyte which has high economic and medicinal values grown in the coastal saline soils. Their PGP activity and effects on host seed germination and seedling growth under salinity stress were also evaluated.

Methods

A total of 126 isolates were obtained from the surface sterilized roots, stems and leaves of L. sinense (Girard) Kuntze. They were initially selected for their ability to produce ACC deaminase as well as other PGP properties such as production of indole-3-acetic acid (IAA), N₂-fixation, and phosphate-solubilizing activities and subsequently identified by the 16S rRNA gene sequencing. For selected strains, seed germination, seedling growth, and flavonoids production in axenically growth L. sinense (Girard) Kuntze seedlings at different NaCl concentrations (0–500 mM) were quantified.

Results

Thirteen isolates possessing ACC deaminase activity were obtained. The 16S rRNA gene sequencing analysis showed them to belong to eight genera: Bacillus, Pseudomonas, Klebsiella, Serratia, Arthrobacter, Streptomyces, Isoptericola, and Microbacterium. Inoculation with four of the selected ACC deaminase-producing strains not only stimulated the growth of the host plant but also influenced the flavonoids accumulation. All four strains could colonize and can be re-isolated from the host plant interior tissues.

Conclusions

These results demonstrate that ACC deaminase-producing habitat-adapted symbiotic bacteria isolated from halophyte could enhance plant growth under saline stress conditions and the PGPE strains could be appropriate as bioinoculants to enhance soil fertility and protect the plants against salt stress.