And 1-aminocyclopropane-1-carboxylate Deaminase Research Articles

Comparative Analysis of Plant Growth-Promoting Rhizobacteria's Effects on Alfalfa Growth at the Seedling and Flowering Stages under Salt Stress.

Alfalfa (Medicago sativa L.), a forage legume known for its moderate salt-alkali tolerance, offers notable economic and ecological benefits and aids in soil amelioration when cultivated in saline-alkaline soils. Nonetheless, the limited stress resistance of alfalfa could curtail its productivity. This study investigated the salt tolerance and growth-promoting characteristics (in vitro) of four strains of plant growth-promoting rhizobacteria (PGPR) that were pre-selected, as well as their effects on alfalfa at different growth stages (a pot experiment). The results showed that the selected strains belonged to the genera Priestia (HL3), Bacillus (HL6 and HG12), and Paenibacillus (HG24). All four strains exhibited the ability to solubilize phosphate and produce indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Among them, except for strain HG24, the other strains could tolerate 9% NaCl stress. Treatment with 100 mM NaCl consistently decreased the IAA production levels of the selected strains, but inconsistent changes (either enhanced or reduced) in terms of phosphate solubilization, ACC deaminase, and exopolysaccharides (EPS) production were observed among the strains. During the various growth stages of alfalfa, PGPR exhibited different growth-promoting effects: at the seedling stage, they enhanced salt tolerance through the induction of physiological changes; at the flowering stage, they promoted growth through nutrient acquisition. The current findings suggest that strains HL3, HL6, and HG12 are effective microbial inoculants for alleviating salt stress in alfalfa plants in arid and semi-arid regions. This study not only reveals the potential of indigenous salt-tolerant PGPR in enhancing the salt tolerance of alfalfa but also provides new insights into the mechanisms of action of PGPR.

Combined application of H2S and a plant growth promoting strain JIL321 regulates photosynthetic efficacy, soil enzyme activity and growth-promotion in rice under salt stress

Salinity stress is one of the most harmful abiotic stresses that inhibit crop growth and grain yield. In this study, a salt-tolerant bacterium was isolated from the soil of the rice rhizosphere and named Myroides sp. JIL321, based on the results of the phylogenetic tree analysis. The strain JIL321 tolerated up to 1, 283.37 mM of NaCl and exhibited positive plant growth-promoting traits, such as the production of indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Therefore, the effects of JIL321 on rice (Oryza sativa L.) under salinity stress were determined. The inoculation of strain JIL321 significantly increased the chlorophyll content and the accumulation of osmotic adjustment substances, such as proline and soluble sugars, in rice expose to salt stress. Additionally, strain JIL321 inoculation significantly enhanced the activities of some enzymes commonly found in soil, such as urease, invertase and catalase. Moreover, the production of hydrogen sulfide (H2S), a pivotal signaling molecule, was also induced in rice by salt stress. Treatment with sodium hydrogen sulfide (NaHS, H2S donor) improved salt stress tolerance of the rice, while treatment with hypotaurine (HT, H2S scavenger) significantly suppressed it. Interestingly, NaHS treatment also improved the production of IAA and ACC deaminase in strain JIL321 under 0 mM and 150 mM salt concentrations. The combined treatment of JIL321 and NaHS could further improve the growth of salt-stressed rice seedlings, most likely due to the interaction effect between H2S and strain JIL321. To our knowledge, this study is the first to demonstrate that the combined use of H2S and plant growth-promoting bacteria could alleviate the adverse effects of salt stress on rice plants, and further verifies the novel role of H2S as a signaling molecule that enhance the tolerance of plant to abiotic stresses.

Soil environment influences plant growth-promotion traits of isolated rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) occur naturally in the rhizosphere, but our understanding of the soil and climatic variables that influence the occurrence of beneficial bacteria is poor. Here, we examined the effects of environmental factors on the occurrence of PGPR in the chickpea rhizosphere soils. A total of 743 rhizobacteria were isolated from the chickpea rhizosphere collected from 74 sampling sites across Australia. Results revealed that the ability of isolates to produce indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase were positively correlated with the potential of rhizobacteria to promote root growth. The amount of IAA production was positively correlated with soil copper, manganese and zinc concentrations, electric conductivity and the aridity index, but negatively correlated with soil carbon (C), nitrogen (N) and phosphorus (P) in the soils from which the PGPR were isolated. Additionally, the ability of PGPR to tolerate metal ion toxicity and water stress was related to their ability to produce IAA. The potential of isolates to solubilise P was negatively correlated with the C/N ratio, N, P, C and magnesium content of the soils but none of the soil environmental factors was correlated with the ACC deaminase activity of the isolates. In a principal component analysis, these environmental variables explained 53 % of the variation in the ability of the rhizobacteria to produce IAA and ACC deaminase and/or to solubilise P. These findings could be applied to the design of an efficient PGPR development strategy that incorporates ecological traits and plant growth-promoting mechanisms to increase chickpea production.

Genome analysis of a salinity adapted Achromobacter xylosoxidans rhizobacteria from the date palm

Rhizospheric bacteria play an indispensable role in plant growth, development, and stress response in plants. This project aims to isolate and functionally characterize plant-growth-promoting rhizobacteria (PGPR) from date palm (Phoenix dactylifera L.) rhizosphere, to investigate its potential uses as a biofertilizer in date palm. Here, we report an Achromobacter xylosoxidans SQU-1 (SQU-1), as a rhizobacteria strain isolated from date palms grown under salinity. The strain was visualized using electron microscopy, identified using protein profiling and 16 S rRNA gene sequencing, functionally characterized, and its genome was sequenced, assembled, and annotated. The results showed that SQU-1 is a Gram-negative flagellated strain and possesses several plant-growth-promoting traits, including the ability to solubilize micronutrients such as zinc, potassium, phosphorus and to produce ammonia, iron siderophores, indole acetic acid (IAA) phytohormone, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. SQU-1 was also able to significantly enhance date palm seed germination and Arabidopsis growth under normal and saline conditions. Whole-genome sequencing of SQU-1 revealed a total of 6,441,875 bp reads that were assembled into 15 scaffolds. Genome sequence analysis indicated the presence of 5968 open reading frames (ORFs), including 5848 coding genes, 56 pseudogenes, and 64 rRNA DNA sequences. Sequence and cluster of orthologous groups (COG) analysis of SQU-1 enabled the identification of potential genes involved in plant growth-promoting characteristics such as ACC DEAMINASE (acdS), D-CYSTEINE DESULFHYDRASE, and various siderophore production and transporter genes. In conclusion, SQU-1 can be a good candidate for a sustainable agricultural system that aims at producing date fruits under saline conditions with minimal usage of chemical fertilizers.

Investigation of ACC-Deaminase and Indole Acetic Acid Producing Bacteria from Rhizospheric Soils in Ağrı Province

Plant growth promoting rhizobacteria (PGPR) have critical role in promoting plant growth and health with various mechanisms. Production of indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity are well-known plant growth promoting (PGP) properties. In the current study; A total of 48 morphologically distinct bacterial colonies were chosen during the isolation of bacteria from various rhizospheric wheat, maize and sainfoin soil samples from agricultural areas in Ağrı-Turkey. The bacteria were isolated from soil samples utilizing by culture-dependent techniques. Then, the strains were visualised for PGP activities such as production acetic acid IAA and ACC deaminase activity. The 16S rRNA sequence similarity of potential PGPR rhizospheric strains demonstrated that strains belong to species Bacillus, Pseudomonas, Microbacterium, Pseudarthrobacter, Arthrobacter and Enterobacter. Totally, 11 of 48 isolates exhibited highly IAA producing and ACC deaminase activity. These results show that IAA producing and ACC deaminase activity of local potential PGPR strains isolated from soil rhizospheric which can appropriate for sustainable agricultural applications in Ağrı province.

ACC deaminase-producing Ensifer adhaerens KS23 enhances proximate nutrient of Pisum sativum L. cultivated in high altitude.

A phytohormone producing, N2-fixing and 1-aminocyclopropane-1-carboxylate (ACC) deaminase synthesizing bacterium Ensifer adhaerens KS23 effectively increased the yield and nutritional contents of Pisum sativum var. Arkel. The isolate KS23 showed positive ACC deaminase activity with 174.2 (nmol of α-ketobutyrate/g-1 biomass½ h-1) a 9.7-fold increase in glutathione S-transferase activity. The proximate analysis exhibited an increased yield of protein (21.45%), carbohydrate (38.90%), sulphur (29.94%) starch (27.52%), total ash (35.57%), fat content (27.5%), nitrogen (24.06%) and hydrogen (17.91%) in treated seeds of P. sativum as compared to untreated crop seeds in field trials at Srikot village, Srinagar-246,174 (Garhwal) India. The most desirable essential and non-essential amino-acids content was also enhanced simultaneously by E. adhaerens KS23 as compared to non-treated crop seeds. This study revealed the enhancement of various nutritional contents resulting in quality improvement and an increase in growth productivity of pea. This study provides an encouraging result that may benefit the marginal income of farmers belonging mainly to hilly regions who are dependent on traditional methods of farming and thus improving their economy.

Ameliorative effect of co-application of Bradyrhizobium japonicum EI09 and Se to mitigate chromium stress in Capsicum annum L.

The present study was conducted to explore the potential of Bradyrhizobium japonicum EI09 (EI09) and selenium (Se) alone or in combination to mitigate hexavalent chromium (Cr6+) stress in Capsicum annum L. Chromium stressed plants exhibited significant reduction in biomass, chlorophyll content and gas exchange characteristics. The inoculated seedlings subjected to Cr6+stress showed improvement in growth, proline content, gas exchange attributes and total soluble proteins. Likewise, inoculated C. annum seedlings exhibited augmented activity of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) under Cr6+ stress. The Cr6+ stress mitigation in inoculated seedlings was ascribed to reduction in malondialdehyde (MDA) content, hydrogen peroxide (H2O2) besides increase activity of flavonoids, proline, phenolic content along with modulation of antioxidative enzymes. The growth-enhancing attributes of bacteria such as indole acetic acid (IAA) content and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity enhanced growth in Cr6+-stressed plants. Moreover, co-treatment of EI09 and 5 µM Se effectively mitigated Cr (VI) stress in C. annum plants. Current studies provide a novel insight into potential of B. japonicum EI09 and Se in reduction of Cr6+ toxicity in C. annum plants.

Role of Inorganic Phosphate Solubilizing Bacilli Isolated from Moroccan Phosphate Rock Mine and Rhizosphere Soils in Wheat (Triticum aestivum L) Phosphorus Uptake.

This work aimed to assess the ability of plant growth-promoting Bacilli isolated from wheat rhizosphere and rock phosphate mine soils to convert inorganic phosphate (Pi) from Moroccan natural phosphate (NP) to soluble forms. The effect of these bacteria on wheat plants in order to increase their phosphorus (P) uptake in vitro was also investigated. Bacteria were isolated from wheat rhizosphere and natural rock phosphate soils and screened for their ability to solubilize Tri-Calcium Phosphate (TCP) and Natural Rock Phosphate (NP), to produce indole-3-acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Isolates were identified by 16S rRNA sequencing and tested for their capacity to increase wheat plants growth and their phosphorus uptake.Twenty-four strains belonging to Bacillus genus isolated from both biotopes were screened for their ability to solubilize Pi. The highest NP solubilization was showed by strains isolated from wheat rhizosphere. Solubilization of Pi was accompanied by organic acid production. Strains produce IAA, siderophore and ACC deaminase. Inoculation assays using efficient NP-solubilizing bacilli strains from both sources showed the ability of these isolates to increase wheat growth and the phosphorus uptake under in vitro conditions. Bacilli strains isolated from rhizosphere soil and natural rock phosphorus soil showed effective solubilization of Pi from rock phosphate. Phosphate solubilizing Bacilli were evaluated for their plant growth promotion under in vitro conditions. Results revealed the positive effect of all strains on biometric parameters and P content of wheat seedlings.

Alleviation of salt stress response in soybean plants with the endophytic bacterial isolate Curtobacterium sp. SAK1

Salinity has been a major abiotic stressor that reduce the productivity. Previous studies reported that endophytic bacteria produce plant stress response hormones, antioxidants, and enzymes such as ACC deaminase. Augmentation of these metabolites and enzymes by endophytes mitigates the stress effects of salinity and improves plant growth and productivity. Bacterial endophytes were isolated from Artemisia princeps Pamp, and evaluated for indole-3-acetic acid (IAA), abscisic acid (ABA), siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production and the ability to solubilize phosphate in the presence of NaCl (100–400 mM). SAK1 was applied to Glycine max cv. Pungsannamul to investigate salinity stress. Our results revealed that with an increase in NaCl concentration, the amount of ABA production in SAK1 increased, whereas IAA levels decreased. Bacterial ABA and JA degrade the reactive oxygen species and protect plants against stressors. Gas chromatography-mass spectrometry (GC-MS) analysis detected different gibberellins (GAs) and organic acids in SAK1. Interestingly, SAK1 inoculation significantly increased plant growth attributes under normal and salinity stress conditions, whereas a decrease in endogenous jasmonic acid and ABA content in the plants was recorded under salinity stress. IAA and GAs enhance number of root tips and hence improve nutrients uptake in plants. Polyphenolic oxidase and peroxidase were alleviated by elevated SAK1 in G. max plants under stress. ACC deaminase of SAK1 resulted deamination of ACC, up to 330 nmol α-ketobutyrate mg−1 h−1 which could be a major reason of ethylene reduction promoting plant growth. SAK1 relieved salinity stress in plants by producing different phytohormones, antioxidants, and ACC deaminase enzyme. SAK1 could be a new addition in batch of plant stress hormone-regulating endophytic bacteria that mitigates the effects of salt stress and promotes plant growth in G. max.

Soil microbial dynamics prediction using machine learning regression methods

Soil microbial dynamics is significant for the soil productivity. The present study explores the application of machine learning based regression methods in the prediction of selected soil microbial dynamics, including bacterial population (BP), phosphate solubilization (PS), and enzyme activities. An experiment was designed in a salt medium with rock phosphate inoculated with the solubilizing microorganism to measure the PS, BP, and 1-Aminocyclopropane-1-carboxylate (ACC) deaminase activity at a different temperature, pH, and incubation period. The artificial neural network (ANN), support vector regression (SVR), Wang and Mendel’s (WM) - fuzzy inference systems (FIS), and subtractive clustering (SC)-FIS methods have been applied in the estimation of PS, BP, and ACC deaminase activity using the experimental conditions. The performance of four regression methods has been evaluated in the terms of the coefficient of determination (R2), root mean square error (RMSE), and correlation coefficient (ρ). The SC-FIS method has better performance than the rest three methods in the prediction of each of the soil microbial dynamics (R2 of 0.99 in the prediction of PS).

Characterization of phosphate solubilizing fluorescent pseudomonads from the rhizosphere of Aloe vera (L.)

ABSTRACTSoil phosphorous (P) deficiency is a major constraint to plant production which is overcome by adding inorganic-phosphate as chemical fertilizers. Fluorescent pseudomonads are the diverse group of bacteria able to mobilize sparingly soluble phosphate form. Total three hundred seven fluorescent Pseudomonas isolates were obtained from the Aloe barbadensis (Miller) rhizosphere. These Pseudomonas strains were further evaluated in vitro for their ability to solubilize phosphate and to produce indole acetic acid (IAA), hydrogen cyanide (HCN), siderophore and 1-aminocyclopropane 1- carboxylate (ACC) deaminase. Fifty three (36.8%) isolates produced IAA and 52 (36.1%) isolates produced siderophores whereas 36 (25.0%) and 31 (21.5%) isolates produced HCN and ACC deaminase, respectively. A positive correlation existed between siderophore and ACC deaminase producers. Cluster analysis showed rhizosphere as the major factor influencing the ecological distribution and physiological characterization of phosphate solubilizing bacteria (PSB). Based on partial 16S rRNA gene sequencing PSB were identified as Pseudomonas putida, Pseudomonas sp. and Pseudomonas plecoglossicida with highest phosphate solubilization ability. In conclusion, these phosphate solubilizing fluorescent pseudomonads would help in understanding their role in phosphorus solubilization and identification of potent phosphorus solubilizers from the rhizosphere of commercially grown A. barbadensis.

Isolation of a potential biocontrol agent Paenibacillus polymyxa NSY50 from vinegar waste compost and its induction of host defense responses against Fusarium wilt of cucumber

Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (FOC) is one of the major destructive soil-borne diseases infecting cucumber. In this study, we screened 60 target strains isolated from vinegar waste compost, from which 10 antagonistic strains were identified to have the disease suppression capacity of bio-control agents. The 16S rDNA gene demonstrated that the biocontrol agents were Paenibacillus polymyxa (P. polymyxa), Bacillus amyloliquefaciens (B. amyloliquefaciens) and Bacillus licheniformis (B. licheniformis). Based on the results of antagonistic activity experiments and pot experiment, an interesting strain of P. polymyxa (named NSY50) was selected for further research. Morphological, physiological and biochemical characteristics indicated that this strain was positive for protease and cellulase and produced indole acetic acid (22.21±1.27μg mL−1) and 1-aminocyclopropane-1-carboxylate deaminase (ACCD). NSY50 can significantly up-regulate the expression level of defense related genes PR1 and PR5 in cucumber roots at the early stages upon challenge with FOC. However, the gene expression levels of a set of defense-related genes, such as the plant nucleotide-binding site (NBS)-leucine-rich repeat (LRR) gene family (e.g., Csa001236, Csa09775, Csa018159), 26kDa phloem protein (Csa001568, Csa003306), glutathione-S-transferase (Csa017734) and phenylalanine ammonia-lyase (Csa002864) were suppressed by pretreatment with NSY50 compared with the single challenge with FOC after nine days of inoculation. Of particular interest was the reduced expression of these genes at disease progression stages, which may be required for F. oxysporum dependent necrotrophic disease development.

Rhizobacterial Pseudomonas spp. Strains Harbouring acdS Gene Could Enhance Metallicolous Legume Nodulation in Zn/Pb/Cd Mine Tailings

Phytostabilisation can benefit from phytostimulatory rhizobacteria. Forty-three bacterial strains were isolated from the roots of the metallicolous legume Anthyllis vulneraria ssp. carpatica grown in a highly contaminated mine tailing (total Cd, Pb and Zn were up to 1200; 34,000; and 170,000 mg kg−1, respectively). We aimed at evaluating their phytostimulatory effects on the development of leguminous metallophytes. Strains were screened for fluorescent siderophores and auxin synthesis, inorganic P solubilisation and 1-amino-cyclopropane-1-carboxylate deaminase (ACCd) activity to define a subset of 11 strains that were inoculated on the leguminous metallophytes A. vulneraria and Lotus corniculatus grown in diluted mine spoil (Zn 34,653; Pb 6842; and Cd 242, all in mg kg−1). All strains were affiliated to Pseudomonas spp. (except two), synthetised auxins and siderophores and solubilised P (except three), and seven of them were ACCd positive. The inoculation effects (shoot-root-nodule biomass, chlorophyll content) depended on legume species and bacterial strain genotype. Phytostimulation scores were unrelated to siderophore/auxin synthesis and P solubilisation rates. Inoculations of the strain nos. 17–43 triggered a 1.2-fold significant increase in the chlorophyll content of A. vulneraria. Chlorophyll content and root biomass of L. corniculatus were significantly increased following the inoculations of the strain nos. 17–22 (1.5–1.4-fold, respectively). The strongest positive effects were related to increases in the nodule biomass of L. corniculatus in the presence of three ACCd-positive strains (1.8-fold), one of which was the highest auxin producer. These data suggest to focus on interactions between ACCd activity and auxin synthesis to enhance nodulation of metallicolous legumes.

Indigenous salt-tolerant rhizobacterium Pantoea dispersa (PSB3) reduces sodium uptake and mitigates the effects of salt stress on growth and yield of chickpea

Salt stress has multiple damaging effects on plants including physiological damage, reduced growth, and productivity. Plant growth-promoting rhizobacteria (PGPR) are one of the valuable options to mitigate the negative effects of this stress. In the present study, native bacteria from chickpea’s rhizosphere were isolated, and checked for their salt tolerance and plant growth-promoting attributes (phosphate (P) solubilization, siderophores, indole-3-acetic acid (IAA) production, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production). One isolate, subsequently identified as Pantoea dispersa, showed appreciable production of IAA (218.3 µg/ml) and siderophores (60.33% SU), P-solubilization (3.64 µg/ml) and ACC deaminase activity (207.45 nmol/mg/h) in the presence of 150 mM NaCl, under laboratory conditions. Salt stress in uninoculated chickpea (GPF2 cultivar) plants induced high accumulation of Na+ ions (3.86 mg g−1 dw) in the leaves, along with significant reduction in K+ uptake, membrane integrity, chlorophyll concentration, and leaf water content, thus resulting in impaired growth of the plant and yield (pods and seeds) in a salt concentration-dependent manner. The damage due to salt stress was restored significantly in plants inoculated with P. dispersa. A significant improvement in biomass (32–34%), pods number (31–34.5%), seeds number (32–35.7%), pods weight (30–32.6%), and seeds weight (27–35%) per plant occurred in salt stress-affected plants, which was associated with significant reduction in Na+ uptake, reduced membrane damage, significantly improved leaf water content, chlorophyll content, and K+ uptake. This study suggests for the first time that native P. dispersa strain PSB3 can be used to alleviate the negative effects of salt stress on chickpea plants and holds the potential to be used as a biofertilizer.

Phyto-extraction of chromium and influence of plant growth promoting bacteria to enhance plant growth

Chromium (Cr) toxicity affects many physiological processes and inhibits plant growth. Plant growth promoting rhizobacteria (PGPR) have ability to improve plant health in contaminated soil as well as degrade toxic Cr. Present investigation was made to examine the role of Pseudomonas putida (ATCC 39213), to enhancing the plant growth and Cr phytoextraction. Three treatments of Cr (low; 150ppm, medium; 250ppm and high; 500ppm) were applied to the E. sativa seedlings, either inoculated with Pseudomonas putida (P. putida) or un-inoculated plants. Results of this study clearly indicate that P. putida inoculation significantly increased plant growth and Cr uptake as compared to un-inoculated plants. Root and shoot length increased 33% and 42%, fresh and dry weight increased 49% and 53% as compared to un-inoculated plants, respectively. However, chlorophyll and proline contents increased 39% and 44%. Physiological parameters of growth indicate that Cr toxicity decreased the plant growth, while inoculation of P. putida overcome the inhibitory effects of Cr and increased growth under Cr stress. Cr uptake by plants was increased 38% with P. putida inoculation. Provision of Indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity by P. putida in the growing media, which may induce the Cr uptake and plant growth under stress condition in E. sativa. The present results offer insight on plant growth promoting rhizobacteria's (PGPRs), such as P. putida, potential to enhance the plant growth by inhibiting the adverse effects of Cr in E. sativa. This study will contribute towards the environmental management of Cr-contaminated areas and enhancing plant growth under Cr stress conditions.

Formulation of bacterial consortia from avocado (Persea americana Mill.) and their effect on growth, biomass and superoxide dismutase activity of wheat seedlings under salt stress

Inoculation of plants with bacteria that produce indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) often has a positive effect on alleviation of salt stress in plants. Here, we isolated, characterized and formulated halotolerant bacterial consortia from avocado trees with the aim of developing biofertilizers to improve avocado production on saline soils. Using wheat as a test plant, experiments were conducted to investigate the effects of selected bacterial consortia on growth, biomass and superoxide dismutase (SOD) activity of wheat seedlings exposed to salt stress (0.25M and 0.45M NaCl) under greenhouse conditions. Among 309 isolates, 17.4% were characterized as halotolerant IAA- and ACCD-producing bacteria. Based on differences in their IAA production and ACCD activities, four consortia were formulated using members of five genera: Enterobacter, Serratia, Microbacterium, Pseudomonas and Achromobacter. Inoculation with selected halotolerant bacterial consortia significantly (P≥0.05) increased the emergence, growth, biomass and SOD activity of wheat seedlings exposed to salt stress. Avocado trees and their rhizosphere soils harbor halotolerant IAA- and ACCD-producing bacteria with the potential to mitigate the salt stress effects on plants. While wheat was useful for screening, further studies are necessary to validate the effects of selected bacterial consortia on avocado growth and yields under saline conditions.

Bioaccumulation of nickel by E. sativa and role of plant growth promoting rhizobacteria (PGPRs) under nickel stress

Phytoremediation potential of plants can be enhanced in association with microbes. Further, many plant growth-promoting rhizobacteria can improve growth under stress. The present study was conducted to investigate the effect of Pseudomonas putida (P. putida) on nickel (Ni) uptake and on growth of Eruca sativa (E. sativa). Three different levels of Ni (low; 150ug/g, medium; 250ug/g and high; 500ug/g) were applied to the soil containing E. sativa seedlings, with or without P. putida. Ni-toxicity was measured by metamorphic parameters including shoot length, root length, biomass, chlorophyll and proline and Ni contents. Inoculation with P. putida increased 34% and 41% in root and shoot length and 38% and 24% in fresh, dry weight respectively, as compared to non-inoculated plants. Similarly, Ni uptake increased by up to 46% following P. putida inoculation as compared to non-inoculated plants. Indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity in the growing media enhanced growth and Ni uptake in E. sativa. The present results offer insight on Plant Growth Promoting Rhizobacteria (PGPR), such as P. putida, for the potential to enhance the plant growth by inhibiting the adverse effects of Ni in E. sativa.

Characterization of Mn-resistant endophytic bacteria from Mn-hyperaccumulator Phytolacca americana and their impact on Mn accumulation of hybrid penisetum

Three hundred Mn-resistant endophytic bacteria were isolated from the Mn-hyperaccumulator, Phytolacca americana, grown at different levels of Mn (0, 1, and 10mM) stress. Under no Mn stress, 90%, 92%, and 11% of the bacteria produced indole acetic acid (IAA), siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, respectively. Under Mn stress, 68–94%, 91–92%, and 21–81% of the bacteria produced IAA, siderophore, and ACC deaminase, respectively. Greater percentages of ACC deaminase-producing bacteria were found in the Mn-treated P. americana. Furthermore, the ratios of IAA- and siderophore-producing bacteria were significantly higher in the Mn treated plant leaves, while the ratio of ACC deaminase-producing bacteria was significantly higher in the Mn treated-roots. Based on 16S rRNA gene sequence analysis, Mn-resistant bacteria were affiliated with 10 genera. In experiments involving hybrid penisetum grown in soils treated with 0 and 1000mgkg−1 of Mn, inoculation with strain 1Y31 was found to increase the root (ranging from 6.4% to 18.3%) and above-ground tissue (ranging from 19.3% to 70.2%) mass and total Mn uptake of above-ground tissues (64%) compared to the control. Furthermore, inoculation with strain 1Y31 was found to increase the ratio of IAA-producing bacteria in the rhizosphere and bulk soils of hybrid penisetum grown in Mn-added soils. The results showed the effect of Mn stress on the ratio of the plant growth-promoting factor-producing endophytic bacteria of P. americana and highlighted the potential of endophytic bacterium as an inoculum for enhanced phytoremediation of Mn-polluted soils by hybrid penisetum plants.

Characterization of ACC deaminase-producing endophytic bacteria isolated from copper-tolerant plants and their potential in promoting the growth and copper accumulation of Brassica napus

One hundred Cu-resistant-endophytic bacteria were isolated from Cu-tolerant plants grown on Cu mine wasteland, of which, eight Cu-resistant and 1-aminocyclopropane-1-carboxylate (ACC) deaminase-producing endophytic bacteria were obtained based on the ACC deaminase activity of the bacteria and characterized with respect to metal resistance, production of ACC deaminase, indole-3-acetic acid (IAA) as well as siderophores and mineral phosphate solubilization. Ralstonia sp. J1-22-2, Pantoea agglomerans Jp3-3, and Pseudomonas thivervalensis Y1-3-9 with higher ACC deaminase activity (ranging from 213 to 370 μM α-ketobutyrate mg −1 h −1) were evaluated for promoting plant growth and Cu uptake of rape grown in quartz sand containing 0, 2.5, and 5 mg kg −1 of Cu in pot experiments. The eight bacteria were found to exhibit different multiple heavy metal resistance characteristics, to show different levels of ACC deaminase activity and to produce indole acetic acid. Seven bacteria produced siderophores and solubilized inorganic phosphate. Pot experiments showed that inoculation with the strains (J1-22-2, Jp3-3, and Y1-3-9) was found to increase the biomass of rape. Increases in above-ground tissue Cu contents of rape cultivated in 2.5 and 5 mg kg −1 of Cu-contaminated substrates varied from 9% to 31% and from 3 to 4-fold respectively in inoculated-rape plants compared to the uninoculated control. The maximum Cu uptake of rape was observed after inoculation with P. agglomerans Jp3-3. The results show that metal-resistant and plant growth promoting endophytic bacteria play an important role in plant growth and Cu uptake which may provide a new endophytic bacterial-assisted phytoremediation of Cu-contaminated environment.

Plantation management induces long-term alterations to bacterial phytohormone production and activity in bulk soil

Phytohormone production and modification by soil bacteria has the potential to influence plant growth and performance. We studied the long term effects of nitrogenous fertilisation and weed control on the concentration of IAA equivalents and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity in bulk soil in a Pinus radiata plantation. IAA equivalent concentrations were increased by weed control and ACC deaminase activity was increased by weed control and fertilisation. Measurements of P. radiata growth were positively correlated with IAA equivalent concentrations. ACC deaminase activity was positively correlated with P. radiata growth only in the absence of fertilisation. These results suggest that plantation management can induce long term effects on soil bacterial phytohormone production and modification, which may influence plant growth.