Perspective of plant growth promoting rhizobacteria (PGPR) containing ACC deaminase in stress agriculture

Ethylene is a gaseous plant growth hormone produced endogenously by almost all plants. It is also produced in soil through a variety of biotic and abiotic mechanisms, and plays a key role in inducing multifarious physiological changes in plants at molecular level. Apart from being a plant growth regulator, ethylene has also been established as a stress hormone. Under stress conditions like those generated by salinity, drought, waterlogging, heavy metals and pathogenicity, the endogenous production of ethylene is accelerated substantially which adversely affects the root growth and consequently the growth of the plant as a whole. Certain plant growth promoting rhizobacteria (PGPR) contain a vital enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which regulates ethylene production by metabolizing ACC (an immediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia. Inoculation with PGPR containing ACC deaminase activity could be helpful in sustaining plant growth and development under stress conditions by reducing stress-induced ethylene production. Lately, efforts have been made to introduce ACC deaminase genes into plants to regulate ethylene level in the plants for optimum growth, particularly under stressed conditions. In this review, the primary focus is on giving account of all aspects of PGPR containing ACC deaminase regarding alleviation of impact of both biotic and abiotic stresses onto plants and of recent trends in terms of introduction of ACC deaminase genes into plant and microbial species.     

Synergistic interactions between the ACC deaminase-producing bacterium Pseudomonas putida UW4 and the AM fungus Gigaspora rosea positively affect cucumber plant growth

Bacteria producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase modulate plant ethylene levels. Decreased ethylene levels increase plant tolerance to environmental stresses and promote legume nodulation. On the contrary, the role of ethylene in mycorrhizal symbiosis establishment is still controversial. In this work, the ACC deaminase-producing strain Pseudomonas putida UW4 AcdS+ and its mutant AcdS(-), impaired in ACC deaminase synthesis, were inoculated alone or in combination with the AM fungus Gigaspora rosea on cucumber. Mycorrhizal and bacterial colonization as well as plant growth and morphometric parameters were measured. The influence of each microorganism on the photosynthetic efficiency was evaluated on the second and fourth leaf. The strain AcdS+, but not the AcdS(-) mutant, increased AM colonization and arbuscule abundance. The mycorrhizal fungus, but not the bacterial strains, promoted plant growth. However, the AcdS+ strain, inoculated with G. rosea, induced synergistic effects on plant biomass, total root length and total leaf projected area. Finally, the photosynthetic performance index was increased by the strain UW4 AcdS+ inoculated in combination with G. rosea BEG9. These results suggest a key role of this enzyme in the establishment and development of AM symbiosis.     

芽孢杆菌对桉树幼苗的促生效果及其ACC脱氨酶活性的研究

【目的】筛选出能显著促进桉树幼苗生长的芽孢杆菌菌株,探究酶活性与桉树幼苗生长的相关性,初步揭示芽孢杆菌对桉树幼苗的促生机制。【方法】以分离自广东广州、阳江桉树林地土壤的32个芽孢杆菌菌株为研究对象,测定桉树幼苗接种盆栽试验以及菌株ACC脱氨酶活性与幼苗N、P养分。【结果】接种菌株2306、2403、2301能够显著促进桉树幼苗高生长和生物量积累,尤以菌株2306的促生效果最佳,其苗高、生物量分别比对照增加53.1%和190.2%。【结论】芽孢杆菌的ACC脱氨酶活性与桉树幼苗高生长相关极显著,与生物量相关显著;而且上述3个菌株均能提高桉树幼苗的N、P含量。研究结果将进一步丰富桉树促生菌资源,促进桉树微生物肥料的开发。     

含ACC脱氨酶的根际细菌提高植物抗盐性的研究进展

盐胁迫是抑制植物生长的主要非生物因素之一,高浓度的盐分不利于植物体的生长和发育,严重时会导致植物细胞及植物体死亡.已有大量实验结果显示含ACC脱氨酶的根际细菌可以缓解高盐对植物的危害.ACC脱氨酶可以降解乙烯的直接前体1-氨基环丙烷-1-羧酸(ACC),从而降低胁迫乙烯的合成量.胁迫乙烯是阻碍植物生长的主要原因.首先介...     

中华补血草内生与根际具ACC脱氨酶活性细菌的筛选及其生物多样性

【目的】获得江苏沿海滩涂盐生药用植物中华补血草内生及根际具有1-氨基环丙烷-1-羧酸(ACC)脱氨酶活性的细菌,研究其遗传多样性和潜在促生活性。【方法】从中华补血草和根际土壤分离筛选具有ACC脱氨酶活性的菌株,对其ACC脱氨酶活性定量检测,通过16S r RNA基因序列分析确定菌株系统发育地位。同时研究其固氮、溶磷、产植物生长素吲哚乙酸(IAA)及耐盐能力。【结果】分离筛选获得18株具有ACC脱氨酶活性的内生与根际细菌,定量检测发现其中有13株菌的ACC脱氨酶含量在20 nmolα-KA/(mg Pr·h)以上,有11株菌可以固氮,7株菌能够解磷,9株菌产生IAA。菌株的Na Cl盐耐受范围多数在0–13%之间。16S r RNA基因测序表明,活性菌株分属于7个属,多样性丰富,节杆菌属(Arthrobacter)为优势类群。其中菌株KLBMP 5180为节杆菌属的潜在新种。【结论】江苏沿海滩涂盐生药用植物中华补血草共生环境中具有丰富多样的具ACC脱氨酶活性的菌株,并存在潜在新物种资源,具有进一步研究价值。     

ACC deaminase positive Enterobacter-mediated mitigation of salinity stress,and plant growth promotion of Cajanus cajan: a lab to field study

Salinity is a major abiotic stress that negatively impacts plant health and soil microbiota. ACC (1-aminocyclopropane carboxylic acid) deaminase producing microorganisms act as natural stress busters that protect plants from different kinds of stresses. The study focused on the isolation of potent, indigenous, multi-trait ACC deaminase producers. The shortlisted ACC deaminase producers were checked for their ability to promote growth of Cajanus cajan, and mitigate stress under laboratory conditions followed by validation of their potency in naturally saline field conditions. Physiological stress markers were assessed to evaluate the impact of salinity in plants treated with ACC deaminase producer, compared to controls. Further, the contribution of ACC deaminase in stress mitigation was demonstrated by using a chemical inhibitor for ethylene biosynthesis. This study presents a polyphasic approach, transitioning from the rhizospheric soil to the laboratory to validation in the field, and puts forth a promising eco-friendly alternative for sustainable agriculture.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-01031-0.     

具有ACC脱氨酶活性的细菌的分离和鉴定

在以ＡＣＣ（α－氨基环丙烷梭酸）为唯一氮源的选择性培养基上,对土壤来源的细菌菌株进行了筛选。通过生长测定、对ＡＣＣ降解的分析,确定了菌株ＡＣＣ脱氨酶的活性,并对菌株进行了系统鉴定。     

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。     

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。     

Promotion of Plant Growth by Bacterial ACC Deaminase

To date, there has been only limited commercial use of plant growth-promoting bacteria in agriculture, horticulture, and silviculture. However, with recent progress toward understanding the mechanisms that these organisms utilize to facilitate plant growth, the use of plant growth-promoting bacteria is expected to continue to increase worldwide. One of the key mechanisms employed by plant growth-promoting bacteria to facilitate plant growth is the lowering of plant ethylene levels by the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase. This article reviews the published work on this enzyme, with an emphasis on its biochemistry, protein structure, genes, and regulation. In addition, this article provides some initial insights into the changes in both plants and ACC deaminase-containing plant growth-promoting bacteria as a consequence of plant-microbe interactions. Finally, a brief discussion of how bacterial ACC deaminase and indoleacetic acid (IAA) together modulate plant growth and development is included.     

旱地小麦根际细菌中产生1-氨基环丙烷-1-羧酸(ACC)脱氨酶菌株的分离和鉴定

采用富集定向筛选法,从旱地小麦的根际土壤中分离到2株产生1-氨基环丙烷-1-羧酸(ACC)脱氨酶的菌株AS和CS。经测定菌株AS和CS的ACC脱氨酶的比活力分别为0.018 6 U/mg和0.016 7 U/mg蛋白。根据培养特征观察和生理生化指标测定结果,结合16S rDNA碱基序列测定和系统发育同源性分析,确定菌株AS和菌株CS分别属于霍氏肠杆菌(Enterobacter hormaechei)和变形斑沙雷氏菌(Serratia proteamaculans)。     

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.     

A colorimetric assay of 1-aminocyclopropane-1-carboxylate (ACC) based on ninhydrin reaction for rapid screening of bacteria containing ACC deaminase

Aims: 1‐Aminocyclopropane‐1‐carboxylate (ACC) deaminase activity is an efficient marker for bacteria to promote plant growth by lowering ethylene levels in plants. We aim to develop a method for rapidly screening bacteria containing ACC deaminase, based on a colorimetric ninhydrin assay of ACC. Methods and Results: A reliable colorimetric ninhydrin assay was developed to quantify ACC using heat‐resistant polypropylene chimney‐top 96‐well PCR plates, having the wells evenly heated in boiling water, preventing accidental contamination from boiling water and limiting evaporation. With this method to measure bacterial consumption of ACC, 44 ACC‐utilizing bacterial isolates were rapidly screened out from 311 bacterial isolates that were able to grow on minimal media containing ACC as the sole nitrogen source. The 44 ACC‐utilizing bacterial isolates showed ACC deaminase activities and belonged to the genus Burkholderia, Pseudomonas or Herbaspirillum. Conclusions: Determination of bacterial ACC consumption by the PCR‐plate ninhydrin–ACC assay is a rapid and efficient method for screening bacteria containing ACC deaminase from a large number of bacterial isolates. Significance and Impact of the Study: The PCR‐plate ninhydrin–ACC assay extends the utility of the ninhydrin reaction and enables a rapid screening of bacteria containing ACC deaminase from large numbers of bacterial isolates.     

具有ACC脱氨酶活性的绞股蓝内生细菌的分离鉴定及其抑菌促生作用

采用富集筛选法从绞股蓝根中筛选得到6株具有ACC脱氨活性的细菌,其中菌株JDG-6、JDG-7、JDG-14、JDG-16、JDG-23均具有较强的分泌铁载体能力,但菌株JDG-32没有产铁载体能力。抑菌试验结果显示,菌株JDG-6、JDG-7、JDG-14和JDG16对一种或多种供试菌有抑菌作用,其中菌株JDG-14能抑制大肠埃希菌、藤黄八叠球菌和白色念球菌的生长。促生试验表明,菌株JDG-6、JDG-7和JDG-14均能促进水稻幼苗根的伸长,其中菌株JDG-14的促生作用最为明显,与对照组相比水稻幼苗的根长和根鲜重分别增长了26%和21%。通过形态特征观察、生理生化试验以及16S rDNA序列分析,菌株JDG-6、JDG-7、JDG-16和JDG-23属于假单胞杆菌属（Pseudomonas）,菌株JDG-14为木糖葡萄球菌（Staphylococcus xylosus）,而菌株JDG-32为枯草芽胞杆菌（Bacillus subtilis）。菌株JDG-6、JDG-7和JDG-14均具有ACC脱氨酶活性和抑菌活性的促生菌,具有农业应用潜力。     

具有ACC脱氨酶活性的麻疯树根际促生菌(PGPR)的分离筛选及系统发育分析

[目的]获得具有产ACC、IAA,铁载体,能固氮或解磷的潜在促生菌株.[方法]通过稀释涂布的方法,从麻疯树根际土壤中分离得到98株细菌,从中选取28株以产l-氨基环丙烷-1-羧酸(ACC)脱氨酶为主要促生指标进行筛选,同时检测了其产吲哚乙酸(IAA)、固氮、解磷及铁载体等促生指标的能力.[结果]结果显示,46％的菌株能产ACC脱氨酶,其含量最高可达到128.308 μmol α-KA/(mg.h),68％的菌株能产生IAA,54％的菌株有固氮的能力,32％的菌株有解磷的能力.少量菌株同时具有产ACC脱氨酶、IAA,固氮,解磷等能力.挑选代表性菌株进行16S rRNA序列分析,这些菌株属于芽孢杆菌属(Bacillus)、节杆菌属(Arthrobacter)、假单胞菌属(Pseudomonas)和产碱杆菌属(Advenella)等8个属,其中多数菌株(50％)属于芽孢杆菌属,系统发育分析表明菌株KLBMP 4817、KLBMP 4821和KLBMP 4824为窄食单胞菌属(Stenotrophomonas)和类芽孢杆菌属(Paenibacillus)的潜在新种.[结论]攀枝花麻疯树根际土壤细菌中含有丰富的遗传多样性,且存在大量的促生菌株.其中,菌株KLBMP 4804产ACC脱氨酶含量最高.菌株KLBMP4820产IAA含量最显著.     

Growth promotion and yield enhancement of peanut (Arachis hypogaea L.) by application of plant growth-promoting rhizobacteria

Although plant growth-promoting rhizobacteria (PGPR) have been reported to influence plant growth, yield and nutrient uptake by an array of mechanisms, the specific traits by which PGPR promote plant growth, yield and nutrient uptake were limited to the expression of one or more of the traits expressed at a given environment of plant–microbe interaction. We selected nine different isolates of PGPR from a pool of 233 rhizobacterial isolates obtained from the peanut rhizosphere on the basis of ACC-deaminase activity. The nine isolates were selected, initially, on the basis of germinating seed bioassay in which the root length of the seedling was enhanced significantly over the untreated control. All the nine isolates were identified as Pseudomonas spp. Four of these isolates, viz. PGPR1, PGPR2, PGPR4 and PGPR7 (all fluorescent pseudomonads), were the best in producing siderophore and indole acetic acid (IAA). In addition to IAA and siderophore-producing attributes, Pseudomonas fluorescens PGPR1 also possessed the characters like tri-calcium phosphate solubilization, ammonification and inhibited Aspergillus niger and A. flavus in vitro. P. fluorescens PGPR2 differed from PGPR1 in the sense that it did not show ammonification. In addition to the traits exhibited by PGPR1, PGPR4 showed strong in vitro inhibition to Sclerotium rolfsii. The performances of these selected plant growth-promoting rhizobacterial isolates were repeatedly evaluated for 3 years in pot and field trials. Seed inoculation of these three isolates, viz. PGPR1, PGPR2 and PGPR4, resulted in a significantly higher pod yield than the control, in pots, during rainy and post-rainy seasons. The contents of nitrogen and phosphorus in soil, shoot and kernel were also enhanced significantly in treatments inoculated with these rhizobacterial isolates in pots during both the seasons. In the field trials, however, there was wide variation in the performance of the PGPR isolates in enhancing the growth and yield of peanut in different years. Plant growth-promoting fluorescent pseudomonad isolates, viz. PGPR1, PGPR2 and PGPR4, significantly enhanced pod yield (23–26%, 24–28% and 18–24%, respectively), haulm yield and nodule dry weight over the control in 3 years. Other attributes like root length, pod number, 100-kernel mass, shelling out-turn and nodule number were also enhanced. Seed bacterization with plant growth-promoting P. fluorescens isolates, viz. PGPR1, PGPR2 and PGPR4, suppressed the soil-borne fungal diseases like collar rot of peanut caused by A. niger and PGPR4 also suppressed stem rot caused by S. rolfsii. Studies on the growth patterns of PGPR isolates utilizing the seed leachate as the sole source of C and N indicated that PGPR4 isolate was the best in utilizing the seed leachate of peanut, cultivar JL24. Studies on the rhizosphere competence of the PGPR isolates, evaluated on the basis of spontaneous rifampicin resistance, indicated that PGPR7 was the best rhizoplane colonizer and PGPR1 was the best rhizosphere colonizer. Although the presence of growth-promoting traits in vitro does not guarantee that an isolate will be plant growth promoting in nature, results suggested that besides ACC-deaminase activity of the PGPR isolates, expression of one or more of the traits like suppression of phytopathogens, solubilization of tri-calcium phosphate, production of siderophore and/or nodulation promotion might have contributed to the enhancement of growth, yield and nutrient uptake of peanut.