Response of spring rape (Brassica napus var. oleifera L.) to inoculation with plant growth promoting rhizobacteria containing 1-aminocyclopropane-1-carboxylate deaminase depends on nutrient status of the plant

Responses of rape (Brassica napus var. oleifera L.) to inoculation with plant growth promoting rhizobacteria, Pseudomonas putida Am2, Pseudomonas putida Bm3, Alcaligenes xylosoxidans Cm4, and Pseudomonas sp. Dp2, containing 1-aminocyclopropane-l-carboxylate (ACC) deaminase were studied using growth pouch and soil cultures. In growth pouch culture, the bacteria significantly increased root elongation of phosphorus-sufficient seedlings, whereas root elongation of phosphorus-deficient seedlings was not affected or was even inhibited by the bacteria. Bacterial stimulation of root elongation of phosphorus-sufficient seedlings was eliminated in the presence of a high ammonia concentration (1 mM) in the nutrient solution. Bacterial effects on root elongation of potassium-deficient and potassium-sufficient seedlings were similar. The bacteria also decreased inorganic phosphate content in shoots of potassium- and phosphorus-sufficient seedlings, reduced ethylene production by phosphorus-sufficient seedlings, and inhibited development of root hairs. The effects of treatment with Ag+, a chemical inhibitor of plant ethylene production, on root elongation, ethylene evolution, and root hair formation were similar to bacterial treatments. The number of bacteria on the roots of phosphorus-deficient seedlings was not limited by phosphorus deficiency. In pot experiments with soil culture, inoculation of seeds with bacteria and treatment with aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis in plants, increased root and (or) shoot biomass of rape plants. Stimulation of plant growth caused by the bacteria was often associated with a decrease in the content of nutrients, such as P, K, S, Mo, and Ba, in shoots, depending on the strain used. The results obtained show that the growth-promoting effects of ACC-utilizing rhizobacteria depend significantly on the nutrient status of the plant.     

ACC deaminase producing Pseudomonas putida strain PSE3 and Rhizobium leguminosarum strain RP2 in synergism improves growth, nodulation and yield of pea grown in alluvial soils

Plant growth promoting rhizobacteria affects the overall performance of plants by one or combination of mechanisms. However, little information is available on how ACC deaminase secreting bacteria enhance crop production. The present study aimed at identifying ACC deaminase producing and phosphate solubilizing bacterial strains and to assess their plant growth promoting activities. Additionally, the effect of two ACC deaminase positive bacterial strains Pseudomonas putida and Rhizobium leguminosarum on pea plants was determined to find a novel and compatible bacterial pairing for developing efficient inoculants for enhancing legume production and reducing dependence on chemical fertilizers. The isolated bacterial cultures were characterized biochemically and by 16S rRNA sequence analysis. The plant growth promoting activities was determined using standard microbiological methods. The impact of P. putida and R. leguminosarum, on pea plants was determined both in pots and in field environments. Of the total 40 bacterial strains, strain PSE3 isolated from Mentha arvenss rhizosphere and RP2 strain from pea nodules produced ACC deaminase, solubilized insoluble phosphate, synthesized indole acetic acid, ammonia, cyanogenic compounds, exopolysaccharides and had antifungal activity. The dual inoculation of P. putida strain PSE3 and R. leguminosarum strain RP2 had largest positive effect and markedly increased the growth, symbiotic characteristics, nutrient pool and quantity and quality of pea seeds. The measured parameters were further augmented when inoculated pea plants were grown in soils treated with urea or DAP. A significant variation in the measured parameters of pea plants was observed under both pot and field trials following microbial inoculation but the bacterial cultures did not differ significantly in growth promoting activities. The results suggest that ACC deaminase positive bacterial cultures endowed with multiple potential can be targeted to develop mixed inoculants for enhancing pea production and hence, to reduce dependence on synthetic fertilizers.     

Pseudomonas brassicacearum strain Am3 containing 1-aminocyclopropane-1-carboxylate deaminase can show both pathogenic and growth-promoting properties in its interaction with tomato

The role of bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity in the interaction between tomato (Lycopersicon esculentum=Solanum lycopersicum) and Pseudomonas brassicacearum was studied in different strains. The phytopathogenic strain 520-1 possesses ACC deaminase activity, an important trait of plant growth-promoting rhizobacteria (PGPR) that stimulates root growth. The ACC-utilizing PGPR strain Am3 increased in vitro root elongation and root biomass of soil-grown tomato cv. Ailsa Craig at low bacterial concentrations (10(6) cells ml-1 in vitro and 10(6) cells g-1 soil) but had negative effects on in vitro root elongation at higher bacterial concentrations. A mutant strain of Am3 (designated T8-1) that was engineered to be ACC deaminase deficient failed to promote tomato root growth in vitro and in soil. Although strains T8-1 and 520-1 inhibited root growth in vitro at higher bacterial concentrations (>10(6) cells ml-1), they did not cause disease symptoms in vitro after seed inoculation, or in soil supplemented with bacteria. All the P. brassicacearum strains studied caused pith necrosis when stems or fruits were inoculated with a bacterial suspension, as did the causal organism of this disease (P. corrugata 176), but the non-pathogenic strain Pseudomonas sp. Dp2 did not. Strains Am3 and T8-1 were marked with antibiotic resistance and fluorescence to show that bacteria introduced to the nutrient solution or on seeds in vitro, or in soil were capable of colonizing the root surface, but were not detected inside root tissues. Both strains showed similar colonization ability either on root surfaces or in wounded stems. The results suggest that bacterial ACC deaminase of P. brassicacearum Am3 can promote growth in tomato by masking the phytopathogenic properties of this bacterium.     

海州香薷（Elsholtzia splendens）根际铜抗性细菌的筛选及生物多样性

摘要：【目的】重金属耐性植物海州香薷根际铜抗性细菌的筛选及生物多样性研究将有助于了解微生物－超富集植物相互关系和植物修复机理、开发微生物－香薷重金属修复新技术。【方法】采用稀释平板涂布法从海州香薷根际筛选铜抗性菌株,测定菌株溶磷和产生吲哚乙酸、铁载体、1-氨基环丙烷-1-羧酸（ACC）脱氨酶的特性,采用16S rDNA限制性酶切多态性分析（amplified rDNA restriction analysis, ARDRA）研究铜抗性细菌的遗传多样性,根据16S rDNA相似性对产ACC脱氨酶的菌株进行了     

Isolation and characterization of ACC deaminase-producing fluorescent pseudomonads, to alleviate salinity stress on canola (Brassica napus L.) growth

Salinity stress is of great importance in arid and semi-arid areas of the world due to its impact in reducing crop yield. Under salinity stress, the amount of 1-aminocyclopropane-1-carboxylate (ACC), a precursor for ethylene production in plants, increases. Here, we conducted research under the hypothesis that isolated ACC deaminase-producing Pseudomonas fluorescens and Pseudomonas putida can alleviate the stressful effects of salinity on canola (Brassica napus L.) growth. The experiments were conducted in the Soil and Water Research Institute, Tehran, Iran. Seven experimental stages were conducted to isolate and characterize ACC deaminase-producing Pseudomonas fluorescens strains and to determine factors enhancing their growth and, consequently, their effects on the germination of canola seeds. Under salinity stress, in 14% of the isolates, ACC deaminase activity was observed, indicating that they were able to utilize ACC as the sole N-source. Bacterial strains differed in their ability to synthesize auxin and hydrogen cyanide compounds, as well as in their ACC deaminase activity. Under salinity stress, the rate of germinating seeds inoculated with the strains of ACC deaminase-producing Pseudomonas fluorescens and Pseudomonas putida, and seedling growth was significantly higher. These results indicate the significance of soil biological activities, including the activities of plant growth-promoting bacteria, in the alleviation of soil stresses such as salinity on plant growth.     

具ACC脱氨酶活性的碱蓬内生细菌的分离、鉴定及其生物学特性

【目的】具有1-氨基环丙烷-1-羧酸(ACC)脱氨酶活性的盐生植物碱蓬内生细菌的分离及生物学特性的研究有助于探索内生细菌与宿主植物耐盐性的关系。【方法】采用研磨法从健康碱蓬植株的根、茎、叶中分离具有ACC脱氨酶活性的碱蓬内生细菌,根据形态特征、生理生化、API鉴定系统和16S rRNA对菌种进行鉴定,并分别测定了菌株产ACC脱氨酶、铁载体、吲哚乙酸、赤霉素、脱落酸、蛋白酶及溶磷、固氮和拮抗病原菌的特性。【结果】将分离得到的内生细菌LP11、SS12、TW1和TW2分别鉴定为栖稻假单胞菌(Pseudomonas oryzihabitans)、假单胞菌(Pseudomonas sp.)、成团泛菌(Pantoea agglomerans)和恶臭假单胞菌(Pseudomonas putida),4株菌除具有较高的ACC脱氨酶活力之外,还可不同程度地产生铁载体、吲哚乙酸、赤霉素和脱落酸,且均有溶磷作用,但无固氮能力及蛋白酶活力,唯有菌株SS12对萝卜枯萎病菌(Fusariumoxysporum f.sp.conglutinans)和黄瓜枯萎病菌(F.oxysporum f.sp.cucumerinum)具有拮抗作用。【结论】从盐生植物碱蓬中分离到的假单胞菌属和泛菌属内生细菌,具有丰富多样的生物学特性。     

Effectiveness of rhizobacteria containing ACC deaminase for growth promotion of peas (Pisum sativum) under drought conditions

A series of experiments were conducted to assess the effectiveness of rhizobacteria containing 1-aminocyclopropane- 1-carboxylate (ACC) deaminase for growth promotion of peas under drought conditions. Ten rhizobacteria isolated from the rhizosphere of different crops (peas, wheat, and maize) were screened for their growth promoting ability in peas under axenic condition. Three rhizobacterial isolates, Pseudomonas fluorescens biotype G (ACC-5), P. fluorescens (ACC-14), and P. putida biotype A (Q-7), were selected for pot trial on the basis of their source, ACC deaminase activity, root colonization, and growth promoting activity under axenic conditions. Inoculated and uninoculated (control) seeds of pea cultivar 2000 were sown in pots (4 seeds/pot) at different soil moisture levels (25, 50, 75, and 100% of field capacity). Results revealed that decreasing the soil moisture levels from 100 to 25% of field capacity significantly decreased the growth of peas. However, inoculation of peas with rhizobacteria containing ACC deaminase significantly decreased the "drought stress imposed effects" on growth of peas, although with variable efficacy at different moisture levels. At the lowest soil moisture level (25% field capacity), rhizobacterial isolate Pseudomonas fluorescens biotype G (ACC-5) was found to be more promising compared with the other isolates, as it caused maximum increases in fresh weight, dry weight, root length, shoot length, number of leaves per plant, and water use efficiency on fresh and dry weight basis (45, 150, 92, 45, 140, 46, and 147%, respectively) compared with respective uninoculated controls. It is highly likely that rhizobacteria containing ACC deaminase might have decreased the drought-stress induced ethylene in inoculated plants, which resulted in better growth of plants even at low moisture levels. Therefore, inoculation with rhizobacteria containing ACC deaminase could be helpful in eliminating the inhibitory effects of drought stress on the growth of peas.     

Methods for isolating and characterizing ACC deaminase-containing plant growth-promoting rhizobacteria

One of the major mechanisms utilized by plant growth-promoting rhizobacteria (PGPR) to facilitate plant growth and development is the lowering of ethylene levels by deamination of 1-aminocyclopropane-1-carboxylic acid (ACC) the immediate precursor of ethylene in plants. The enzyme catalysing this reaction, ACC deaminase, hydrolyses ACC to α -ketobutyrate and ammonia. Several bacterial strains that can utilize ACC as a sole source of nitrogen have been isolated from rhizosphere soil samples. All of these strains are considered to be PGPR based on the ability to promote canola seedling root elongation under gnotobiotic conditions. The treatment of plant seeds or roots with these bacteria reduces the amount of ACC in plants, thereby lowering the concentration of ethylene. Here, a rapid procedure for the isolation of ACC deaminase-containing bacteria, a root elongation assay for evaluating the effects of selected bacteria on root growth, and a method of assessing bacterial ACC deaminase activity are described in detail. This should allow researchers to readily isolate new PGPR strains adapted to specific environments.     

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.     

Characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing <Emphasis Type="Italic">Methylobacterium oryzae</Emphasis> and interactions with auxins and ACC regulation of ethylene in canola (<Emphasis Type="Italic">Brassica campestris</Emphasis>)

The possible interaction of the plant hormones auxin and ethylene and the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing bacteria on ethylene production in canola (Brassica campestris) in the presence of inhibitory concentrations of growth regulators were investigated. The effects of auxin (indole-3-acetic acid and 2,4-dichlorophenoxy acetic acid), auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid, ethylene precursor 1-aminocyclopropane-1-carboxylate and ethylene synthesis inhibitor l-α-(2-aminoethoxyvinyl)glycine hydrochloride on root elongation were concentration dependent. Exogenous addition of growth regulators influences the enzyme activities of ethylene production and we have presented here evidences that support the hypothesis that inhibitory effects of auxin on root elongation are independent of ethylene. Additionally, we have proved that inoculation of ACC deaminase containing Methylobacterium oryzae sequester ACC exuded from roots and hydrolyze them lowering the concentration of ACC in root exudates. However, the inhibitory actions of exogenous additions of auxins could not be ameliorated by bacterial inoculation that reduces ethylene concentration in canola seedlings.     

Growth of canola (Brassica napus) in the presence of plant growth-promoting bacteria and either copper or polycyclic aromatic hydrocarbons

Growth of canola (Brassica napus) seeds treated with plant growth-promoting bacteria in copper-contaminated and polycyclic aromatic hydrocarbon (PAH)-contaminated soils was monitored. Pseudomonas asplenii AC, isolated from PAH-contaminated soil, was transformed to express a bacterial gene encoding 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and both native and transformed bacteria were tested for growth promotion. Inoculation of seeds, grown in the presence of copper or creosote, with either native or transformed P. asplenii AC significantly increased root and shoot biomass. Native and transformed P. asplenii AC and transformed P. asplenii AC encapsulated in alginate were equally effective at promoting plant growth in copper-contaminated soils. In creosote-contaminated soils the native bacterium was the least effective, and the transformed encapsulated bacterium was the most effective in growth promotion.     

Plant Growth-Promoting Bacteria Facilitate the Growth of Barley and Oats in Salt-Impacted Soil: Implications for Phytoremediation of Saline Soils

Plant growth-promoting bacteria (PGPB) strains that contain the enzyme 1-amino- cyclopropane-1-carboxylate (ACC) deaminase can lower stress ethylene levels and improve plant growth. In this study, ACC deaminase-producing bacteria were isolated from a salt-impacted (～50 dS/m) farm field, and their ability to promote plant growth of barley and oats in saline soil was investigated in pouch assays (1% NaCl), greenhouse trials (9.4 dS/m), and field trials (6–24 dS/m). A mix of previously isolated PGPB strains UW3 (Pseudomonas sp.) and UW4 (P. sp.) was also tested for comparison. Rhizobacterial isolate CMH3 (P. corrugata) and UW3+UW4 partially alleviated plant salt stress in growth pouch assays. In greenhouse trials, CMH3 enhanced root biomass of barley and oats by 200% and 50%, respectively. UW3+UW4, CMH3 and isolate CMH2 also enhanced barley and oat shoot growth by 100%–150%. In field tests, shoot biomass of oats tripled when treated with UW3+UW4 and doubled with CHM3 compared with that of untreated plants. PGPB treatment did not affect salt uptake on a per mass basis; higher plant biomass led to greater salt uptake, resulting in decreased soil salinity. This study demonstrates a method for improving plant growth in marginal saline soils. Associated implications for salt remediation are discussed.     

Root colonization and growth promotion of winter wheat and pea by Cellulomonas spp. at different temperatures

Plant-growth-promoting bacteria isolated from the rhizosphere andphyllosphere were analysed for their colonization and growth-promoting effectson winter wheat and pea at different temperatures. The investigations werecarried out in pot experiments using loamy sand in Germany. The colonization ofstrains Cellulomonas sp. 21/2 andCellulomonas sp. 43 in the rhizosphere of winter wheat andpea were much better at 16 °C than that at 26°C. The inoculation with effective bacterial strainssignificantly increased the root and shoot growth of winter wheat and pea at 16more than at 26 °C. Bacterial inoculation also resulted insignificantly higher amount of N, P, and K contents of plant components.     

Effects of inoculation of plant-growth promoting bacteria on Ni uptake by Indian mustard

In this study, among a collection of Ni resistant bacterial strains isolated from serpentine soil, two plant growth promoting bacteria (PGPB), Ps29C and Bm4C were selected based on their ability to utilize ACC as the sole N source and promote seedling growth in roll towel assay. The Ni resistant PGPB, Ps29C and Bm4C were characterized as Pseudomonas sp. and Bacillus megaterium, respectively, on the basis of their 16s rDNA sequences. Assessment of the parameters of plant growth promotion revealed the intrinsic ability of the strains for the production of IAA, siderophore and solubilization of insoluble phosphate. Further, the plant growth promoting activity of Ps29C and Bm4C on the Indian mustard (Brassica juncea) were assessed with different concentrations of Ni in soil. Inoculation of Ps29C or Bm4C promoted plant growth and protected the plant from Ni toxicity. However, the maximum growth was observed in the plants inoculated with strain Bm4C. Inoculation with Ps29C or Bm4C had little influence on the accumulation of Ni in root and shoot system, but produced a much larger aboveground biomass. The present observations showed that the strains Ps29C and Bm4C protect the plants against the inhibitory effects of nickel, probably due to the production of IAA, siderophore and solubilization of phosphate. The above results provided a new insight into the phytoremediation of Ni contaminated soil.     

Effect of a Nickel-Tolerant ACC Deaminase-Producing Pseudomonas Strain on Growth of Nontransformed and Transgenic Canola Plants

Four bacterial strains were isolated from soils at nickel-contaminated sites based on their ability to utilize 1-aminocyclopropane-1-carboxylate (ACC) as a sole source of nitrogen. The four isolates were all identified as Pseudomonas putida Biovar B, and subsequent testing revealed that they all exhibited traits previously associated with plant growth promotion (i.e., indoleacetic acid and siderophore production and ACC deaminase activity). These four strains were also tolerant of nickel concentrations of up to 13.2 mM in the culture medium. The strain, HS-2, selected for further characterization, was used in pot experiments to inoculate both nontransformed and transgenic canola plants (expressing a bacterial ACC deaminase gene in its roots). Plants inoculated with the HS-2 strain produced an increase in plant biomass as well as in nickel (Ni) uptake by shoots and roots. The results suggest that this strain is a potential candidate to be used as an inoculant in both phytoremediation protocols and in plant growth promotion.     

Role of heavy metal resistant Ochrobactrum sp. and Bacillus spp. strains in bioremediation of a rice cultivar and their PGPR like activities

The present study demonstrates the metal toxicity ameliorating and growth promoting abilities of three different bacterial isolates when applied to rice as host plant. The three bacterial strains included a cadmium resistant Ochrobactrum sp., a lead resistant Bacillus sp. and an arsenic resistant Bacillus sp. designated as CdSP9, PbSP6, and AsSP9, respectively. When these isolates were used as inocula applied to metal-treated rice plants of variety Satabdi, the germination percentage, relative root elongation (RRE), amylase and protease activities were increased. The toxic effect of metal was reduced in presence of these bacteria. The overall biomass and root/shoot ratio were also enhanced by bacterial inoculation. Hydroponic studies showed that the superoxide dismutase (SOD) activity and malondialdehyde (MDA) level, which had been increased in the presence of metal stress in rice roots, were lowered by the bacterial inoculation. In addition, all three strains were 1-aminocyclopropane-1-carboxylate (ACC) deaminase and catalase positive, whereas siderophore producing ability was lacking in PbSP6. However, both PbSP6 and AsSP9 were protease positive and could hydrolyse starch. The data indicate that these bacteria have promise for bioremediation as well as for plant growth promotion.     

Rhizobacteria that produce auxins and contain 1‐amino‐cyclopropane‐1‐carboxylic acid deaminase decrease amino acid concentrations in the rhizosphere and improve growth and yield of well‐watered and water‐limited potato (Solanum tuberosum)

Plant‐growth‐promoting rhizobacteria (PGPR) utilise amino acids exuded from plant root systems, but hitherto there have been no direct measurements of rhizosphere concentrations of the amino acid 1‐amino‐cyclopropane‐1‐carboxylic acid (ACC) following inoculation with PGPR containing the enzyme ACC deaminase. When introduced to the rhizosphere of two potato (Solanum tuberosum) cultivars (cv. Swift and cv. Nevsky), various ACC deaminase containing rhizobacteria (Achromobacter xylosoxidans Cm4, Pseudomonas oryzihabitans Ep4 and Variovorax paradoxus 5C‐2) not only decreased rhizosphere ACC concentrations but also decreased concentrations of several proteinogenic amino acids (glutamic acid, histidine, isoleucine, leucine, phenylalanine, serine, threonine, tryptophan, tyrosine, valine). These effects were not always correlated with the ability of the bacteria to metabolise these compounds in vitro, suggesting bacterial mediation of root amino acid exudation. All rhizobacteria showed similar root colonisation following inoculation of sand cultures, thus species differences in amino acid utilisation profiles apparently did not confer any selective advantage in the potato rhizosphere. Rhizobacterial inoculation increased root biomass (by up to 50%) and tuber yield (by up to 40%) in pot trials, and tuber yield (by up to 27%) in field experiments, especially when plants were grown under water‐limited conditions. Nevertheless, inoculated and control plants showed similar leaf water relations, indicating that alternative mechanisms (regulation of phytohormone balance) were responsible for growth promotion. Rhizobacteria generally increased tuber number more than individual tuber weight, suggesting that accelerated vegetative development was responsible for increased yield.     

荧光假单胞菌对食用菌的促生作用及其机理

从小麦根际分离到1株对食用菌有较强促生作用的荧光假单胞菌,命名为假单胞菌P2-10(Pseudomonas sp.P2-10)。该菌株与平菇天达300(Pleurotus ostreatus Td 300)、杏鲍菇杏6(Pleurotus eryngii X6)或鸡腿菇瑞7(Coprinus comatus R7)混合培养,可显著提高这些食用菌菌丝生长速度及诱导并促进子实体的形成和发育。假单胞菌P2-10对食用菌的促生作用来自其代谢产物,可能是通过其1-氨基环丙烷-1-羧酸(ACC)脱氨酶降解食用菌产生的ACC、减少食用菌乙烯的合成及乙烯对菌丝生长和子实体发育的抑制作用。     

Characterization of bacterial communities associated with Brassica napus L. growing on a Zn-contaminated soil and their effects on root growth

The interaction between plant growth-promoting bacteria (PGPB) and plants can enhance biomass production and metal tolerance of the host plants. This work aimed at isolating and characterizing the cultivable bacterial community associated with Brassica napus growing on a Zn-contaminated site, for selecting cultivable PGPB that might enhance biomass production and metal tolerance of energy crops. The effects of some of these bacterial strains on root growth of B. napus exposed to increasing Zn and Cd concentrations were assessed. A total of 426 morphologically different bacterial strains were isolated from the soil, the rhizosphere, and the roots and stems of B. napus. The diversity of the isolated bacterial populations was similar in rhizosphere and roots, but lower in soil and stem compartments. Burkoholderia, Alcaligenes, Agrococcus, Polaromonas, Stenotrophomonas, Serratia, Microbacterium, and Caulobacter were found as root endophytes exclusively. The inoculation of seeds with Pseudomonas sp. strains 228 and 256, and Serratia sp. strain 246 facilitated the root development of B. napus at 1,000 µM Zn. Arthrobacter sp. strain 222, Serratia sp. strain 246, and Pseudomonas sp. 228 and 262 increased the root length at 300 µM Cd.     

Non-pathogenic Staphylococcus strains augmented the maize growth through oxidative stress management and nutrient supply under induced salt stress

The present study was conducted to elucidate the role of phytobeneficial bacteria to control the cellular oxidative damage in maize (Zea mays L.) plants caused by salinity. Bacteria were isolated from the rhizosphere of kallar grass (Leptochloa fusca L.) through serial dilution method and taxonomically identified on the basis of their 16S ribosomal RNA gene sequencing. In vitro phosphate solubilization, indole-3-acetic acid (IAA) synthesis, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity were evaluated by solubilization index measurement, colorimetric method, and turbidity assay, respectively. In the pot experiment, the impact of single and mixed inoculation of these strains at four levels (0, 50, 100, and 200 mM) of salt stress was evaluated in terms of growth and physiological response of maize plants to salinity. The bacterial strains (STN-1, STN-5, and STN-14) were taxonomically classified as Staphylococcus spp. At 5% NaCl level, the strains demonstrated substantial potential for phosphate solubilization, ACC deaminase activity, and IAA production both with and without tryptophan. The inoculation of strains STN-1, STN-5, and mixed inoculation resulted in substantial growth improvement of maize plants along with increased antioxidant enzyme activity and decreased levels of reactive oxygen species. In addition, single inoculation of STN-1 and STN-5 along with mixed inoculation augmented the uptake of N, P, K, and Ca+2 and reduced Na+ uptake. Current results demonstrated that the strains STN-1 and STN-5 modulated stress-responsive mechanisms and regulated ion balance in induced salinity to promote maize growth.