Screening of free-living rhizospheric bacteria for their multiple plant growth promoting activities

Plant growth promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. In search of efficient PGPR strains with multiple activities, a total of 72 bacterial isolates belonging to Azotobacter, fluorescent Pseudomonas, Mesorhizobium and Bacillus were isolated from different rhizospheric soil and plant root nodules in the vicinity of Aligarh. These test isolates were biochemically characterized. These isolates were screened in vitro for their plant growth promoting traits like production of indoleacetic acid (IAA), ammonia (NH(3)), hydrogen cyanide (HCN), siderophore, phosphate solubilization and antifungal activity. More than 80% of the isolates of Azotobacter, fluorescent Pseudomonas and Mesorhizobium ciceri produced IAA, whereas only 20% of Bacillus isolates was IAA producer. Solubilization of phosphate was commonly detected in the isolates of Bacillus (80%) followed by Azotobacter (74.47%), Pseudomonas (55.56%) and Mesorhizobium (16.67%). All test isolates could produce ammonia but none of the isolates hydrolyzed chitin. Siderophore production and antifungal activity of these isolates except Mesorhizobium were exhibited by 10-12.77% isolates. HCN production was more common trait of Pseudomonas (88.89%) and Bacillus (50%). On the basis of multiple plant growth promoting activities, eleven bacterial isolates (seven Azotobacter, three Pseudomonas and one Bacillus) were evaluated for their quantitative IAA production, and broad-spectrum (active against three test fungi) antifungal activity. Almost at all concentration of tryptophan (50-500 microg/ml), IAA production was highest in the Pseudomonas followed by Azotobacter and Bacillus isolates. Azotobacter isolates (AZT(3), AZT(13), AZT(23)), Pseudomonas (Ps(5)) and Bacillus (B(1)) showed broad-spectrum antifungal activity on Muller-Hinton medium against Aspergillus, one or more species of Fusarium and Rhizoctonia bataticola. Further evaluation of the isolates exhibiting multiple plant growth promoting (PGP) traits on soil-plant system is needed to uncover their efficacy as effective PGPR.     

多功能植物根际促生菌对东北黑土区玉米的促生效果

应用微生物肥料改良土壤是提高土壤及化肥养分利用率的重要途径之一,但微生物肥料的效果受作物及生态条件的影响较大,目前适合东北地区玉米生产的微生物肥料应用研究较少。本研究针对我国东北黑土类型及气候特点,从当地玉米根际土中筛选分离出5株具有不同程度的合成生长素(IAA)、溶磷、解钾、产铁载体等多功能的植物根际促生菌MZ1、MZ2、MZ3、MZ4和MZ5;生态适应性研究发现5株菌均有不同程度的耐盐、耐干旱、耐酸碱以及耐农药等特性;16S rRNA基因序列分析鉴定出它们分别属于鞘氨醇单胞菌、肠杆菌、假单胞菌、芽孢杆菌和根瘤菌;玉米田间试验结果显示,在减施50%氮肥的条件下, 与不接种对照相比,接种MZ1、MZ3和MZ5可增产19.9%~25.0%。因此,MZ1、MZ3和MZ5具有发展为适合东北地区土壤和气候环境的玉米微生物肥料的潜力。     

植物根际促生菌作用机制研究进展

植物在生长过程中可能会遭受许多生物和非生物因素胁迫,从而降低生物产量. 人们已知一些植物在不同因素的刺激诱导下,能系统化建立抵抗或忍受不利因素的机制,植物根际促生菌（PGPR）就是其中一类能定殖于根系并促进植物生长的细菌.本文对PGPR促生机制进行归纳和总结,系统阐述了诱导体系抗性和诱导体系产生忍耐力两大促生机制.PGPR的作用机制的多样性暗示着其可能在更多的农业生态系统中得到应用.     

Experimental and mathematical simulation of plant growth promoting rhizobacteria and plant interaction under cadmium stress

Bacterial inoculants of the commercially available plant growth promoting rhizobacteria (PGPR) Arthrobacter mysorens 7, Flavobacterium sp. L30, and Klebsiella mobilis CIAM 880 were selected to obtain ecologically safe barley crop production on cadmium (Cd) polluted soils. All the PGPR immobilized 24–68% soluble cadmium from soil suspension. A. mysorens 7 and K. mobilis CIAM 880 were highly resistant to Cd and grew in up to 1 and 3 mmol CdCl₂ on DAS medium respectively. All PGPR were able to fix nitrogen (276–1014 nmol mg^–1 bacterial DW) and to produce indole acetic acid (IAA) (126–330 nmol mg^–1 bacterial DW) or ethylene (4.6–13.5 nmol bacterial DW). All the PGPR actively colonized barley root system and rhizosphere and significantly stimulated root elongation of barley seedlings (up to 25%), growing on soil containing 5 or 15 mg Cd kg^–1 of soil. Created in the simulation mathematical model confirms our hypothesis that PGPR beneficial effect on barley growing under Cd-stress is a complex process. One of mechanisms underlying this effect might be increase of bacterial migration from rhizoplane to rhizosphere, where PGPR bind soluble free Cd ions in biologically unavailable complex forms. Among the studied PGPR K. mobilis CIAM 880 was the most effective inoculant. Inoculation with K. mobilis CIAM 880 of barley plants growing on Cd contaminated soil (5 mg Cd kg^–1 of soil) under field conditions increased by 120% grain yield and 2-fold decreased Cd content in barley grain. The results suggest that the using K. mobilis CIAM 880 is an effective way to increase the plant yield on poor and polluted areas.     

Role of plant growth promoting rhizobacteria and Ag-nano particle in the bioremediation of heavy metals and maize growth under municipal wastewater irrigation

The investigation evaluated the role of plant growth promoting rhizobacteria (PGPR) and Ag-nano particle on the growth and metabolism of maize irrigated with municipal wastewater (MW). Three PGPR isolated from MW were identified on the basis of 16S-rRNA gene sequence analyses as Pseudomonas sp., Pseudomonas fluorescence, and Bacillus cereus. The municipal waste water was used to irrigate the maize seeds inoculated with 3 isolated PGPR. The isolated PGPR had catalase and oxidase enzymes, solubilize insoluble bound phosphate and exhibit antifungal and antibacterial activities. The colony forming unit (cfu) of the PGPR was inhibited by Ag-nano particle, but was stimulated by the municipal wastewater. The Ag-nano particles augmented the PGPR induced increase in root area and root length. The root-shoot ratio was also changed with the Ag-nano particles. The plants irrigated with municipal wastewater had higher activities of peroxidase and catalase which were further augmented by Ag-nano particle. The Ag- nano particle application modulated level of ABA (34%), IAA (55%), and GA (82%), increased proline production (70%) and encountered oxidative stress and augmented the bioremediation potential of PGPR for Pb, Cd, and Ni. Municipal wastewater needs to be treated with PGPR and Ag nano particle prior to be used for irrigation. This aims for the better growth of the plant and enhanced bioremediation of toxic heavy metals.     

Soil salinity and pH in Japanese mangrove forests and growth of cultivated mangrove plants in different soil conditions

Soil conditions of mangrove forests in southern Japan were found to correlate largely with zonal distributions of the species.Kandelia candel grew in soils with low salinity and low pH,Avicennia marina, Rhizophora stylosa andSonneratia alba in soils with high salinity and high pH, andBruguiera gymnorrhiza in soil with a wide range of pH but limited range of salinity.Lumnitzera racemosa colonized soil with a wide range of pH and medium salinity. Seedlings ofKandelia candel, Bruguiera gymnorrhiza andRhizophora stylosa were planted in soils with differing salinity and pH. Optimum seedling growth ofKandelia, Bruguiera andRhizophora occurred when plants were cultivated in soils similar to those of their natural habitats, suggesting that growth of mangrove species and their zonal distributions were regulated by salinity and soil pH.     

Characterization of cadmium-resistant bacteria for its potential in promoting plant growth and cadmium accumulation in Sesbania bispinosa root

The cadmium (Cd) resistant bacteria were isolated from soils of Damanganga river, Vapi, and identified 11 potential Cd resistant bacteria based on 16S rDNA sequences. The Cd resistant bacteria belonged to four different genera: Providencia spp., Morganella sp., Stenotrophomonas sp., and Bacillus spp. The assessment of plant growth-promoting (PGP) parameters revealed that the Cd tolerant bacteria showed one or more PGP properties. Further, a pot experiment was conducted to elucidate the effects of Cd resistant bacteria on the plant growth and the uptake of Cd by Sesbania bispinosa. The bacterized seedlings recorded 36.0–74.8% and 21.2–32.9% higher root and shoot lengths, respectively, in Cd amended soil compared with control. The Cd mobilization in the root of S. bispinosa by microbial inoculants ranged from 0.02 ± 0.01 to 1.11 ± 0.06 ppm. The enhanced concentrations of Cd accumulation in S. bispinosa roots correspond to the effect of the bacterial strains on metal mobilization in soil. The present observations showed that the Cd resistant strains protect the plants against the inhibitory effects of Cd, probably due to the production of PGP properties. The present results provided a new insight into the phytoremediation of Cd contaminated soil.     

Alleviation of salt stress by plant growth regulators and IAA producing bacteria in wheat

The action of phytohormone producing bacteria and plant growth regulators on germination and seedling growth of wheat under saline conditions were studied. Seed dormancy enforced by salinity (100 mM NaCl) was substantially alleviated and the germination was promoted by gibberellin, auxin, zeatin, and ethephon from 54 to 97%. The IAA producing bacterial strains Pseudomonas aureantiaca TSAU22, Pseudomonas extremorientalis TSAU6 and Pseudomonas extremorientalis TSAU20 significantly increased seedling root growth up to 25% in non-salinated conditions and up to 52% at 100 mM NaCl, compared to control plants. It is concluded that growth regulators considerably alleviated salinity-induced dormancy of wheat seeds. The facts mentioned above make it possible to recommend root colonizing bacteria that produce phytohormone to alleviate salt stress of wheat grown under conditions of soil salinity.     

The role of mycorrhizae and plant growth promoting rhizobacteria (PGPR) in improving crop productivity under stressful environments

Both biotic and abiotic stresses are major constrains to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes also show synergistic as well as antagonistic interactions with other microbes in the soil environment. These interactions may be vital for sustainable agriculture because they mainly depend on biological processes rather than on agrochemicals to maintain plant growth and development as well as proper soil health under stress conditions. A number of research articles can be deciphered from the literature, which shows the role of rhizobacteria and mycorrhizae alone and/or in combination in enhancing plant growth under stress conditions. However, in contrast, a few review papers are available which discuss the synergistic interactions between rhizobacteria and mycorrhizae for enhancing plant growth under normal (non-stress) or stressful environments. Biological interactions between PGPR and mycorrhizal fungi are believed to cause a cumulative effect on all rhizosphere components, and these interactions are also affected by environmental factors such as soil type, nutrition, moisture and temperature. The present review comprehensively discusses recent developments on the effectiveness of PGPR and mycorrhizal fungi for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review. Growth promotion by single and dual inoculation of PGPR and mycorrhizal fungi under stress conditions have also been discussed and reviewed comprehensively.     

Influence of inoculation with plant growth promoting rhizobacteria (PGPR) on tomato plant growth and nematode reproduction under greenhouse conditions

Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J₂/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.     

Decreasing prevalence of rhizosphere IAA producing and seedling root growth promoting bacteria with barley development irrespective of protozoan grazing regime

Barley was grown in soil with either bacteria and a mixed protozoan community (Mixed protozoa) or bacteria and a single vahlkampfiid amoebal species (Single amoeba). We assessed the influence of plant age (day 29, 43 and 57 after sowing) on two aspects of rhizosphere bacterial functioning: (1) the proportion of indole-3-acetic acid (IAA) producing bacteria and (2) the effect of mixed rhizosphere bacterial assemblages on barley seedling root growth in an agar based assay. The proportion of IAA producers was significantly lower at day 57 than at day 29 and 43, and mixed bacterial assemblages extracted from rhizospheres of 29 days old plants were significantly less harmful to seedling growth than bacterial assemblages from older plants. Hence both assays indicated that bacterial communities from rhizospheres of older plants were less beneficial for root growth than bacterial communities from younger plants. Genetic fingerprinting of rhizosphere bacterial communities was compared by use of length heterogeneity polymerase chain reaction (LH-PCR). This analysis showed a clear succession from the inoculum bacterial community with a rather low diversity to a community with much higher diversity at day 29. However, diversity did not change after day 29, and no relationship between protozoan treatment nor plant age and genetic fingerprinting was found. Responsible Editor: Petra Marschner     

A new bio-formulation containing plant growth promoting rhizobacterial mixture for the management of sheath blight and enhanced grain yield in rice

Three plant growth promoting rhizobacterial (PGPR) strains, PF1,FP7 and PB2, were tested alone and in combinations for suppression ofrice sheath blight disease and promotion of plant growth underglasshouse and field conditions. The mixture of PGPR strainssignificantly reduced the sheath blight incidence when applied as eitherbacterial suspension through seed, root, foliar and soil application inglasshouse conditions, or as talc-based formulation under fieldconditions, compared to the respective individual strains. The averagemean of disease reduction was 29.2% for single strains and45.1% for mixtures. In addition to disease suppression, treatmentwith mixture of PGPR strains promoted plant growth in terms of increasedplant height and number of tillers, and ultimately grain yield. Theaverage increases in yield for single strains were 17.7%, and25.9% in case of mixture. Mixture of three PGPR strains reduceddisease and promoted growth to a level equivalent to two strainmixtures. Though seed treatment of either single strain or strainmixtures alone could reduce the disease, subsequent application to root,leaves or soil further reduced the disease and enhanced the plantgrowth. The mixture consisting of PF1 plus FP7 was the most effective inreducing the disease and in promoting plant growth and grainyield.     

镍胁迫下产铁载体细菌对花生的促生性

【目的】挖掘镍耐受性强、产铁载体活性高的植物根际促生细菌,研究镍胁迫下产铁载体细菌对花生的促生作用及其对花生吸收镍的影响。【方法】利用CAS(Chrome azurol S)培养基对花生根际产铁载体细菌定性筛选及定量测试获得产铁载体能力强的菌株,16S r RNA基因相似性及系统进化分析鉴定产铁载体细菌,并用含Ni~(2+)牛肉膏蛋白胨培养基测试细菌对Ni的耐受性;通过花生盆栽实验,测试花生的株高、根长、生物量、氮磷钾含量及镍含量来分析镍胁迫下产铁载体细菌对花生的影响。【结果】从花生根际分离筛选产铁载体芽孢杆菌5株,其中HSGJ1产铁载体能力最强,培养2 d后产156.56 mg/L的铁载体。HSGJ1对Ni~(2+)具有较强的耐受性,最小致死浓度为150 mg/L。在50、100 mg/kg的Ni~(2+)盆栽基质中,HSGJ1能够有效地促进花生的生长、增加花生的生物量及氮磷钾含量,并使花生根部和地上部分的镍含量降低。【结论】产铁载体芽孢杆菌HSGJ1是一株优良的植物根际促生细菌,可应用于镍污染农耕土壤的作物种植中,以提高作物在镍胁迫下的抗逆性,降低作物对镍的富集量,具有较好的应用价值。     

Metabolic demand and growth of juveniles of Centropomus parallelus as function of salinity

The effect of salinity and time of exposure on metabolism and growth of juveniles of fat snook, Centropomus parallelus, were investigated. Food conversion efficiency (FCE), specific growth rate (SGR), oxygen consumption, ammonia excretion rate and O:N (oxygen/nitrogen) ratio were assessed on groups of fat-snook (mean weight 2 g) acclimated for 15- and 30-day periods, to 5‰, 20‰ and 30‰ salinities. For 15-day period, differences between FCEs as well as SGRs at different salinities were not significant. For 30-day period, however, these differences were significant between 5‰ and the other salinities, with the highest and lowest values at 5‰ and 30‰, respectively, for both parameters. Salinity and acclimation period exerted significant influence on the oxygen consumption, ammonia excretion and the O:N ratio of juveniles of C. parallelus. The lowest and highest oxygen consumption was at 20‰ for 15- and 30-day period, respectively. Differences in oxygen consumption between fishes maintained at 5‰ and at 30‰ were not significant, at each period, while between those maintained at 5‰ and 20‰, and at 20‰ and 30‰ differences were significant. Ammonia excretion rates were significantly different between all salinities, at each period, and between periods at each salinity, except at 30‰. The highest and lowest rates were found at 5‰ and 30‰, respectively. The highest O:N ratio for 15-day period was at 30‰ with no difference between those at 5‰ and 20‰. For 30-day period, differences of O:N ratio were significant between salinities. The effect of acclimation period on the O:N was significant only at 20‰. Although C. parallelus is a fish species adapted to face a wide variation of environmental salinity, results show that juvenile fishes kept at different salinities, in laboratory, found better condition to efficiently channel the energy of food into growth at 5‰ for both acclimation periods.     

Effects of environmental salinity and 17alpha-methyltestosterone on growth and oxygen consumption in the tilapia, Oreochromis mossambicus

Effects of environmental salinity and 17α-methyltestosterone (MT) on growth and oxygen consumption were examined in the tilapia, Oreochromis mossambicus. Yolk-sac fry were collected from brood stock in fresh water (FW). After yolk-sac absorption, they were assigned randomly to one of four groups: FW, MT treatment in FW, seawater (SW) and MT treatment in SW. All treatment groups were fed to satiation three times daily. The fish reared in SW (both control and MT-treated groups) grew significantly larger than either group in FW from day 43 throughout the experiment (195 days). The fish fed with MT added to their feed grew significantly larger than their respective controls from day 85 in FW and in SW until the end of the experiment. The routine metabolic rate (RMR) was determined monthly from month 2 (day 62) to month 5 (day 155). A significant negative correlation was seen between RMR and body mass in all treatment groups. Among fish of the same age, the SW-reared tilapia had significantly lower RMRs than the FW-reared fish. The MT-treated fish in SW showed significantly lower RMRs than the SW control group at months 3–5, whereas MT treatment in FW significantly increased the RMR at month 3. Comparison of regression lines between RMR and body mass indicates that MT treatment in FW caused a significant increase in oxygen consumption at a given mass of the fish, whereas MT treatment was without effect on RMR in SW-reared fish. These results clearly indicate that SW-rearing and MT treatment accelerate growth of tilapia, and that RMR decreases as fish size increased. It is also likely that the increased RMR and growth in MT-treated tilapia in FW may be due to the metabolic actions of MT, although the reason for the absence of MT treatment in SW is unclear.     

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.     

烤烟根际烟碱降解细菌的多样性及其促生特性分析

【背景】挖掘兼具烟碱降解和植物根际促生细菌(Plant Growth-Promoting Rhizobacteria,PGPR)功能的细菌资源,有助于保护土壤质量,实现绿色种植。【目的】分析烤烟根际细菌多样性,筛选可降解高浓度烟碱的PGPR。【方法】采用纯培养法在选择性培养基上分离烟碱降解细菌。通过BOXA1R-PCR分析技术、16SrRNA基因测序及系统发育树构建,对菌株的遗传多样性和分类学地位进行分析。进一步评价了菌株的吲哚乙酸(Indole-3-Acetic Acid,IAA)活性、溶磷能力、病原菌拮抗能力等PGPR指标,以筛选出高效PGPR,最后通过盆栽试验验证其促生效果。【结果】分离得到58株烟碱降解细菌,根据BOXA1R-PCR指纹图谱选取11株菌进行16S rRNA基因序列测定,结果表明,58株菌分别属于芽孢杆菌属(Bacillus)、假单胞菌属(Pseudomonas)、拉乌尔菌属(Raoultella)和短波单胞菌属(Brevundimonas)4个属,以芽孢杆菌属(Bacillus)为优势菌属。58株细菌中48.28%的菌株可产IAA,27.59%具备溶磷能力,37.93%具备纤维素降解能力,G2-13、G2-3及HT2-8因促生与抗病特性突出而被筛选为目标功能菌。盆栽试验结果表明,G2-13菌株对幼苗生长的促进作用明显,可使株高与地上部鲜重分别增加33.05%与53.32%。【结论】烤烟根际存在较为丰富多样的烟碱降解细菌,它们在种植业上具有潜在的应用价值。     

Azotobacter: A potential bio-fertilizer for soil and plant health management

Stressor (biotic as well as abiotic) generally hijack the plant growth and yield characters in hostile environment leading to poor germination of the plants and yield. Among the plant growth promoting rhizobacteria, Azotobacter spp. (Gram-negative prokaryote) are considered to improve the plant health. Various mechanisms are implicated behind improved plant health in Azotobacter spp. inoculated plants. For example, acceleration of phytohormone like Indole-3-Acetic Acid production, obviation of various stressors, nitrogen fixation, pesticides and oil globules degradation, heavy metals metabolization, etc. are the key characteristics of Azotobacter spp. action. In addition, application of this bacteria has also become helpful in the reclamation of soil suggesting to be a putative agent which can be used in the transformation of virgin land to fertile one. Application of pesticides of chemical origin are being put on suspension mode as the related awareness program is still on. As far as the limitations of this microbe is concerned, commercial level formulations availability is still a great menace. Present review has been aimed to appraise the researchers pertaining to utility of Azotobacter spp. in the amelioration of plant health in sustainable agroecosystem. The article has been written with the target to gather maximum information into single pot so that it could reach to the dedicated researchers.