ACC Deaminase Activity Research Articles

Field performance of bacterial inoculants to alleviate water stress effects in wheat (Triticum aestivum L.)

Plant growth promoting bacteria (PGPB) containing 1-aminocyclopropane-1-carboxylate (ACC) deaminase can play an important role in abiotic stress tolerance in plants, particularly drought. The objective of this study was to evaluate bacterial strains Variovorax paradoxus RAA3, Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 for their ability to alleviate drought stress in wheat in field experiments under irrigated and rain-fed conditions in the Uttarkhand region of India. In this study, ACC deaminase producing bacterial strains Pseudomonas palleroniana DPB16, Pseudomonas sp. UW4 and Variovorax paradoxus RAA3 were evaluated for their efficiency in improving growth, nutrient content and yield of wheat varieties, HD2967 (drought sensitive) and PBW660 (drought tolerant) under rainfed (drought) and irrigated conditions. Bacterial inoculants increased grain and straw yields at both sites, however the response to inoculation was considerably higher under rainfed conditions (64 to 90% increase with inoculation) compared to that observed under irrigated conditions (22 to 40% increase with inoculation). Of the three seed-coated inoculants tested, strain RAA3 maximally improved grain yield (28.2%, 47.4%), straw yield (11.2%, 26.0%) and harvest index (10.6%, 15.3%) under irrigated and rainfed conditions, respectively, compared to non-inoculated crops. The relative expression of the drought responsive gene aquaporin (TaTIP1;1), in response to inoculation, was significantly higher (3.34-fold) in the wheat variety PBW 660, as compared to the drought sensitive variety HD 2967 in which the expression level of aquaporin was unaffected. Under rainfed conditions, the relative mRNA level of the helicase gene WDH45 was significantly higher in HD 2967 (1.54-fold) than the PBW 660 (3.69-fold). Bacterial inoculation caused significant positive changes in plant biochemical and antioxidant properties compared to uninoculated plants. Overall, the results show that the selected PGPB containing ACC deaminase activity along with other plant growth promoting characteristics are effective inoculants for improving wheat yields in irrigated and rainfed field experiments.

Engineering banana endosphere microbiome to improve Fusarium wilt resistance in banana

BackgroundPlant microbiome highlights the importance of endosphere microbiome for growth and health of the host plant. Microbial community analysis represents an elegant way to identify keystone microbial species that have a more central position in the community. The aim of this study was to access the interactions between the keystone bacterial species and plants during banana Fusarium wilt process, by comparing the endophytic bacterial and fungal community in banana roots and shoot tips during growth and wilting processes. The keystone bacterial species were isolated and further engineered to improve banana wilt resistance.ResultsBanana endosphere microbiome structure varied during plant growth and wilting processes. Bacterial and fungal diversity in the shoot tips and roots increased with the development of the banana plantlets. The bacterial groups belonging to the Enterobacteriaceae family with different relative abundances were detected in all the samples. The Klebsiella spp. might be the keystone bacteria during the growth of banana plantlets. The relative abundance of Fusarium associated with the wilt disease did not increase during the wilting process. The endophytic Enterobacteriaceae strains Enterobacter sp. E5, Kosakonia sp. S1, and Klebsiella sp. Kb were isolated on Enterobacteriaceae selective medium and further engineered by expressing 1-aminocyclopropane-1-carboxylate (ACC) deaminase on the bacterial cell walls (designated as E5P, S1P, and KbP, respectively). Pot experiments suggested that plants inoculated with strains E5, E5P, S1, and S1P increased resistance to the Fusarium wilt disease compared with the controls without inoculation, whereas the Klebsiella inoculation (Kb and KbP) did not increase the wilt resistance. Compared with the inoculation with the wild strains E5 and S1, the inoculation with engineered strains E5P and S1P significantly increased wilt resistance and promoted plant growth, respectively. The results illustrated that the keystone species in the banana microbiome may not be dominant in numbers and the functional role of keystone species should be involved in the wilt resistance.ConclusionThe ACC deaminase activity of engineered bacteria was essential to the Fusarium wilt resistance and growth promotion of banana plants. Engineering keystone bacteria in plant microbiome with ACC deaminase on the cell walls should be a promising method to improve plant growth and disease resistance.

ACC deaminase plays a major role in Pseudomonas fluorescens YsS6 ability to promote the nodulation of Alpha- and Betaproteobacteria rhizobial strains.

Ethylene acts as a major regulator of the nodulation process of leguminous plants. Several rhizobial strains possess the ability to modulate plant ethylene levels through the expression of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase; however, rhizobia present low enzymatic activities. One possible alternative to this problem resides on the use of free-living bacteria, such as Pseudomonas, presenting high levels of ACC deaminase activity that may be used as adjuvants in the nodulation process by decreasing inhibitory ethylene levels. Nevertheless, not much is understood about the specific role of ACC deaminase in the possible role of free-living bacteria as nodulation adjuvants. Therefore, this work aims to study the effect of ACC deaminase in the plant growth-promoting bacterium, Pseudomonas fluorescens YsS6, ability to facilitate alpha- and beta-rhizobia nodulation. The ACC deaminase-producing P. fluorescens YsS6 and its ACC deaminase mutant were used in co-inoculation assays to evaluate their impact in the nodulation process of alpha- (Rhizobium tropici CIAT899) and beta-rhizobia (Cupriavidus taiwanensis STM894) representatives, in Phaseolus vulgaris and Mimosa pudica plants, respectively. The results obtained indicate that the wild-type P. fluorescens YsS6, but not its mutant defective in ACC deaminase production, increase the nodulation abilities of both alpha- and beta-rhizobia, resulting in an increased leguminous plant growth. Moreover, this is the first report of the positive effect of free-living bacteria in the nodulation process of beta-rhizobia. The modulation of inhibitory ethylene levels by free-living ACC deaminase-producing bacteria plays an important role in facilitating the nodulation process of alpha- and beta-rhizobia.

Physiological Diversity of Spitsbergen Soil Microbial Communities Suggests Their Potential as Plant Growth-Promoting Bacteria.

The objective of the study was to assess the physiological diversity and metabolic activity of the soil bacterial communities inhabiting Spitsbergen soils in search of bacterial abilities facilitating plant growth promotion. In the soil, the total number of culturable microorganisms, the number of their individual physiological groups (including Siderophore Synthesizing; SSB and Phosphate Solubilizing Bacteria; PSB), the dehydrogenase (DH) activity, and the ability to utilize sources of C, N, P (EcoPlate) were analysed. In bacterial isolates, siderophores production, ACC (1-aminocyclopropane-1-carboxylate) deaminase (ACCD) activity, IAA (indole-3-acetic acid) synthesis were examined. The isolates were applied to the seeds of Phaseolus coccineus regarding their germination and root length. The results showed differences between copio- and oligotrophic bacteria. A usually high number of SSB was accompanied by the raised number of PSB. A bigger number of SSB was connected with low values of Fe in the soil. High DH activity was assisted by greater number of copio- and oligotrophic bacteria, raised average well color development value, and N and C contents in the soil. Germination index was more alike relative seed germination than relative root growth. IAA concentration and ACCD activity were conversely related. Synthesis of siderophores was matched with ACCD activity and its high level was combined with elevated germination index. In spite of different localization of soil samples, some isolates proved similar traits of activity. Distinct affiliation of isolates and their various localizations were displayed. Among all isolates tested, some possessed one main trait of activity, but most of them had two or more significant features for potential plant growth stimulation. These isolates could be an important source of useful bacteria.

Screening of Rice Apoplast Associated Endophytic Bacterial Isolates for Moisture Stress Tolerance and Plant Growth Promoting Traits

Investigations were made to identify, screen and characterize rice apoplastic fluid endophytic bacterial strains for osmotic stress tolerance and plant growth promoting activity. These bacterial strains were identified phylogentically as Bacillus subtilis TSAC5, Bacillus subtilis TSAA2, Bacillus sp. R2AA10, Bacillus cereus R2AA7, Bacillus marisflavi TSAC7, Cupriavidus alkaliphilus TSAC1, Delftia sp. TSAC2, Janibacter melonis R2AA1, Microbacterium oleivorans R2AA6, Kocuria rosea R2AA5, Pseudomonas aeruginosa NAAI3 and Sphingobium yanoikuyae R2AI1. Of these 12 strains, eight were obtained from drought tolerant rice varieties such as Anna R4 and IR DRT 64 and four from normal rice variety CO51. These endophytes exhibited varied level of osmotic stress tolerance created using different concentrations of PEG 6000 (-1.5, -3.0, -4.0, -4.5, -5.0 and -5.5 MPa) under in vitro conditions in liquid and solid medium. Among the 12 strains, Cupriavidus alkaliphilus TSAC1, Delftia sp. TSAC2, Bacillus marisflavi TSAC7, Janibacter melonis R2AA1, Kocuria rosea R2AA5, Pseudomonas aeruginosa NAAI3 and Sphingobium yanoikuyae R2AI1 showed moisture stress tolerance up to -5.5 MPa. Further increase in moisture stress of -6.0 MPa inhibited growth of 12 tested strains. These strains also exhibited Indole acetic acid (IAA), gibberellic acid (GA3) and extracellular polysaccharide (EPS) production and also showed ACC deaminase (ACCD) activity. Maximum extracellular proline production was found in Bacillus marisflavi TSAC7 under both normal and water stressed conditions. Higher IAA productivity was registered in Janibacter melonis R2AA1 followed by Cupriavidus alkaliphilus TSAC1 and Sphingobium yanoikuyae R2AI1 in the absence of PEG 6000. In the presence of PEG 6000 Delftia sp. TSAC2 recorded maximum IAA productivity. Bacillus subtilis TSAA2 showed greater ACC deaminase activity. EPS production was in the order of Pseudomonas aeruginosa NAAI3 followed by Sphingobium yanoikuyae R2AI1. Sphingobium yanoikuyae R2AI1 produced maximum quantity of GA3 both under normal and water stressed condition. None of the tested strains indicated insoluble phosphate, silicate and zinc solubilisation.

Plant growth promoting ability of ACC deaminase producing rhizobacteria native to Sunflower (Helianthus annuus L.)

Abstract Rhizobacteria inhabiting the soil adhering to the root of the host plants are generally recognized to possess plant growth promoting properties. In the present study, a total of 120 rhizobacterial isolates from native soil samples of sunflower were isolated and screened for their ACC deaminase (ACCd) activity and plant growth promoting properties. A significant ACCd activity ranging between 322.55 and 2085.06 nmol of α-ketobutyrate mg−1 of protein h−1 was observed in 44 isolates with the maximum activity offered by Bacillus subtilis Rhizo SF 48. The rhizobacteria which produced more than 50% α-ketobutyrate were selected to evaluate their efficacy to promote the plant growth under laboratory and greenhouse conditions in sunflower. All the ten ACCd positive isolates were found to exhibit at least four different PGP traits and three were found antagonistic to Fusarium oxysporum. The seed treatment with ACCd producing PGPR also significantly enhanced both seed and vegetative growth parameters compared to control with a maximum enhancement offered by B. subtilis Rhizo SF 48. The findings of the study highlight the efficacy of ACCd producing PGPR in promoting growth parameters in sunflower plants upon seed treatment further warranting to test their ability in the suppression of biotic and abiotic stress.

Biofertilizer/biopesticide potentiality of zinc solubilizing Pseudomonas aeruginosa FA-9 and Enterobacter sp. FA-11 isolated from the wheat rhizosphere grown in arid zone

Bacterial strains were obtained from wheat rhizosphere and screened for zinc solubilization on agar plates. Two strains FA-9 and FA-11 were found efficient for Zn solubilizing activity and were identified as Pseudomonas aeruginosa and Enterobacter sp. by 16S rRNA and gyrase (gyrB) genes analysis, respectively. The strain FA-9 produced a clear zone diameter of 63 mm, 60 mm and 51 mm on agar plate amended with different zinc ores. The strain FA-11 produced a zone diameter of 17 mm with zinc carbonate and 20 mm with zinc oxide while no zone was observed with zinc phosphate. Both strains showed no visible activity with ZnS ore. Similarly, FA-9 and FA-11 increased maximum soluble zinc content (102 µg ml−1 and 45 µg ml−1) from zinc carbonate ore as compared to zinc oxide ore (102 µg ml−1 and 45 µg ml−1) in liquid broth. It was noted that both strains exhibited less potential (7 µg ml−1 and 0.57 µg ml−1) to solubilize ZnS ore in liquid broth. A comparison between agar plate assay and liquid broth quantification shows that agar plate assay does not present the solubilizing potential of ZSB precisely. The strains FA-9 and FA-11 produced auxin with l-tryptophan (3.25 µg ml−1 and 2.86 µg ml−1) and without l-tryptophan (1.23 µg ml−1 and 1.02 µg ml−1). Both strains expressed exo-polysaccharides (EPS) and siderophores activity along with phosphate (P) solubilization, ACC deaminase and antifungal activities. The ACC deaminase and N-fixation activity was confirmed by the amplification of acdS and nifH genes respectively.

Silicate Solubilization and Plant Growth Promoting Potential of Rhizobium Sp. Isolated from Rice Rhizosphere

Silicon is a beneficial plant nutrient with a vital role in maintaining plant growth and enhancing tolerance to both biotic and abiotic stresses. The polymeric insoluble silica present in soils is solubilised during weathering to release monosilicic acid into the soil solution which is the bioavailable form of silicon absorbed by plants. In the present study, a silicate solubilizing bacterial isolate IIRR-1 from rhizopshere soil of rice was characterized for its potential to release soluble silica from insoluble inorganic (Ca, Al, K and Mg) silicates and biogenic materials like diatomaceous earth, siliceous earth, rice husk and rice straw. Incubation studies revealed the ability of the isolate to colonise and grow on all insoluble silicates leading to increased release of silica (12.45–60.15% over control) into culture media by the process of acidolytic (pH 4.5) dissolution of silicates. The isolate, besides possessing additional mineral (P, K and Zn) solubilising capacities, also exhibited phytostimulatory behaviour by producing IAA (0.95 + 0.14 μg IAA /μg bacterial cell protein) and ACC deaminase activity (2.52 + 0.73 μg α ketobutyrate /μg bacterial cell protein/24 h) that modulates the ethylene levels in plant. Furthermore, the isolate successfully colonized rice seedling roots and improved seedling vigour by 29.18% as compared to uninoculated control. The isolate identified as Rhizobium sp. has the potential to be employed as a plant beneficial bacterium for accelerating the weathering process and increasing the rhizosphere available silica concentration.

Evaluation of ACC-deaminase-producing rhizobacteria to alleviate water-stress impacts in wheat (Triticum aestivum L.) plants.

Application of plant-growth-promoting rhizobacteria (PGPR) is an environmentally sustainable option to reduce the effects of abiotic and biotic stresses on plant growth and productivity. Bacteria isolated from rain-fed agriculture field soils in the Central Himalaya Kumaun region, India, were evaluated for the production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase. Those producing ACC deaminase in high amounts were evaluated for their potential to improve wheat (Triticum aestivum L.) plant growth under irrigated and water-stress conditions in two glasshouse experiments. Some of the isolates also showed other plant-growth-promoting (PGP) traits, e.g., N2 fixation, siderophore production, and phosphate solubilization; however, strains with higher ACC deaminase activity showed the greatest effects. These were Variovorax paradoxus RAA3; Pseudomonas spp. DPC12, DPB13, DPB15, DPB16; Achromobacter spp. PSA7, PSB8; and Ochrobactrum anthropi DPC9. In both simulated irrigated and water-stress conditions, a single inoculation of RAA3 and a consortium of DPC9 + DPB13 + DPB15 + DPB16 significantly improved wheat plant growth and foliar nutrient concentrations and caused significant positive changes in antioxidant properties compared with noninoculated plants especially under water stress. These findings imply that PGPB having ACC deaminase activity together with other PGP traits could potentially be effective inoculants to improve the growth of wheat plants in water-stressed rain-fed environments.

Biodiversity of methylotrophic microbial communities and their potential role in mitigation of abiotic stresses in plants

Methylotrophic bacterial community is very important group of bacteria utilizing reduced carbon compounds and plays significant role in plant growth promotion (PGP), crop yield and soil fertility for sustainable agriculture. Abiotic and biotic stresses are very important factors affecting PGP in agriculture. A vast number of microbial communities play an important role in abiotic stress tolerance. The PGP methylotrophic microbes have been reported well enough to mitigate different types of biotic and abiotic stresses. The abiotic stress tolerance was well documented by several methylotrophic bacterial communities such as Hyphomicrobium, Methylarcula, Methylobacillus, Methylobacterium, Methylocapsa, Methylocella, Methyloferula, Methylohalomonas, Methylomonas, Methylophilus, Methylopila, Methylosinus, Methylotenera, Methylovirgula and Methylovorus. The abiotic stress tolerance ability of different methylotrophs and their colonization in different parts of plants under severe low temperature, high temperature, drought and salt stress conditions have been investigated in various studies. The methylotrophic communities help in proliferation of plant directly through solubilization of phosphorus, potassium and zinc, production of phytohormones viz., auxins and cytokinins; production of Fe-chelating compound, biological nitrogen fixation and ACC-deaminase activities or indirectly through productions of ammonia, siderophores and secondary metabolites. The auxin and cytokinin secreted by methylotrophs influence seed germination and plant root growth and help plants to endure water stress. On the plant surface, the abundant methylotrophs exude osmo-protectants such as sugars and alcohols which ultimately help to protect the plants from desiccation and excessive radiations. The utilisation of these potent methylotrophic strains may facilitate proper crop production, PGP by ameliorating abiotic stresses.

Mechanisms of the IAA and ACC-deaminase producing strain of Trichoderma longibrachiatum T6 in enhancing wheat seedling tolerance to NaCl stress

BackgroundTrichoderma species, a class of plant beneficial fungi, may provide opportunistic symbionts to induce plant tolerance to abiotic stresses. Here, we determined the possible mechanisms responsible for the indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase) producing strain of Trichoderma longibrachiatum T6 (TL-6) in promoting wheat (Triticum aestivum L.) growth and enhancing plant tolerance to NaCl stress.ResultsWheat treated with or without TL-6 was grown under different levels of salt stress in controlled environmental conditions. TL-6 showed a high level of tolerance to 10 mg ml− 1 of NaCl stress and the inhibitory effect was more pronounced at higher NaCl concentrations. Under NaCl stress, the activity of ACC-deaminase and IAA concentration in TL-6 were promoted, with the activity of ACC-deaminase increased by 26% at the salt concentration of 10 mg ml− 1 and 31% at 20 mg ml− 1, compared with non-saline stress; and the concentration of IAA was increased by 10 and 7%, respectively (P < 0.05). The increased ACC-deaminase and IAA concentration in the TL-6 strain may serve as an important signal to alleviate the negative effect of NaCl stress on wheat growth. As such, wheat seedlings with the ACC-deaminase and IAA producing strain of TL-6 treatment under NaCl stress increased the IAA concentration by an average of 11%, decreased the activity of ACC oxidase (ACO) by an average of 12% and ACC synthase (ACS) 13%, and decreased the level of ethylene synthesis and the content of ACC by 12 and 22%, respectively (P < 0.05). The TL-6 treatment decreased the transcriptional level of ethylene synthesis genes expression, and increased the IAA production genes expression significantly in wheat seedlings roots; down-regulated the expression of ACO genes by an average of 9% and ACS genes 12%, whereas up-regulated the expression of IAA genes by 10% (P < 0.05). TL-6 treatments under NaCl stress decreased the level of Na+ accumulation; and increased the uptake of K+ and the ratio of K+/Na+, and the transcriptional level of Na+/H+ antiporter gene expression in both shoots and roots.ConclusionsOur results indicate that the strain of TL-6 effectively promoted wheat growth and enhanced plant tolerance to NaCl stress through the increased ACC-deaminase activity and IAA production in TL-6 stain that modulate the IAA and ethylene synthesis, and regulate the transcriptional levels of IAA and ethylene synthesis genes expression in wheat seedling roots under salt stress, and minimize ionic toxicity by disturbing the intracellular ionic homeostasis in the plant cells. These biochemical, physiological and molecular responses helped promote the wheat seedling growth and enhanced plant tolerance to salt stress.

Impact of Native ST-PGPR (Bacillus pumilus; EU927414) on PGP Traits, Antioxidants Activities, Wheat Plant Growth and Yield under Salinity

The rhizobacterial isolate ‘121’ identified as Bacillus pumilus-EU927414, which was a rich source of PGP traits like IAA, gibberellins, phosphate solubilisers and siderophore production at 8% NaCl (w/v). This isolate showed synergistic behaviour of PGP traits with its compatible ST-PGPRs like three-fold increases in IAA content in T9 combination (EU927414-B. pumilus + EU927408-B. aquimaris +EU742146-Bacillus sp.). Synergistic behaviour of B. pumilus-EU927414 was also observed in the case of ACC deaminase activities in T9 at 8% NaCl (w/v). Growth and yield of wheat crop in saline soil (ECe>3.4 dSm−1) were enhanced by the inoculation of native ST-PGPR (salt tolerantplant growth promoting rhizobacteria) under half a dose of recommended synthetic fertilisers (N: P: K) as observed in two successive cropping seasons. Salinity tolerant wheat cultivar K-7903 was used to evaluate the effect of ST-PGPRs in the saline field. Antioxidants activities like SOD, APX, CAT and GR along with proline, TSS, RS content were increased in T9 treated leaves of wheat plant at 60 days, followed by 90 days. The N, P and K contents in plant leaf were significantly increased due to inoculation of compatible ST-PGPRs including B. Pumilus-EU927414. The results showed reduced sodium content in T9 treated wheat plant's leaf at 90 days, followed by 60 days. The yield of wheat was 24% increases with the inoculation of T9 combination, followed by T3 combination (EU927414-B. pumilus + EU927412-Pseudomonas medicona + EU927410-Arthrobacter sp.), when compared with control.

Application of Plant Growth Promoting Rhizobacteria in Growth Enhancement of a Multipurpose crop Crotalaria Juncea (Sunhemp) in Saline Soil

Salinity is a major abiotic stress which limits the crop productivity. In this study salt tolerant bacteria were isolated from root nodules of Crotalaria juncea plant collected from different salt affected sites. Salt tolerance activity of all the isolates was checked and it was observed that 47% of the isolates showed up to 8% salt tolerance. On the basis of morphological, biochemical and physiological characterization isolates were found to be Gram negative, rod shaped and motile bacteria that belong to rhizobia. All the isolates also showed nodulation in host plant. Most of the isolates were positive for various plant growth promoting attributes. On the basis of salt tolerance and plant growth promoting characterization isolate CR6 was selected for further studies. CR6 showed positive results for phosphate and zinc solubilisation, and was able to produce indole acetic acid (IAA), siderophore and exopolysaccharides (EPS). CR6 also showed nitrogen fixation and ACC deaminase activity. CR6 was applied on Crotalaria plant to enhance growth in saline soil. After application of CR6 seed germination rate and various growth parameters such as root length, shoot length, nodule number, fresh weight, dry weight, leaves count, chlorophyll and proline content of plants were enhanced in comparison to control, hence CR6 can be used as an efficient bioinoculant to enhance crop growth in saline soil.

Psychrotolerant bacteria isolated from the leaf apoplast of cold-adapted wild plants improve the cold resistance of bean (Phaseolus vulgaris L.) under low temperature

We have isolated psychrotolerant bacteria from the leaf apoplast of cold-adapted wild plants and aimed to investigate their effect on the cold resistance of bean (Phaseolus vulgaris L.). Based on the findings of 16S rRNA gene sequence analysis, 20 isolates belonging to 5 bacteria species (Pseudomonas fragi, P. chloropaphis, P. fluorescens, P. proteolytica and Brevibacterium frigoritolerans) were identified in the leaf apoplastic fluid of Draba nemorosa, Galanthus gracilis, Colchicum speciousum, Scilla siberica, Erodium cicutarium, respectively. We have determined that 6 of the 20 isolates have exhibited ACC (1-aminocyclopropane-1-carboxylate) deaminase activity and secreted different extracellular proteins under cold condition (+4 °C) compared to normal growth condition (28 °C). The six isolates were then inoculated independently of each other to the leaves of 10-day-old bean seedlings growing under normal conditions (25/22 °C, 16/8 h photoperiod), and the inoculated and uninoculated (control) seedlings were transferred to cold (9/5 °C, 16/8 h photoperiod) for 3 days. The bacterial inoculations have decreased freezing injury, ice nucleating activity and lipid peroxidation content in parallel with the decrease of reactive oxygen species level such as O2.- and H2O2 in the inoculated seedlings compared to the control. In addition, the inoculations of the isolates have stimulated the activity of apoplastic antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione reductase. The results show that the inoculations improve the cold resistance of bean seedlings and the psychrotolerant bacterial isolates can be evaluated within the group of plant growth promoting bacteria (PGPB) which can increase tolerance of cold-sensitive crops.

Synthesis of Indoleacetic Acid, Gibberellic Acid and ACC-Deaminase by Mortierella Strains Promote Winter Wheat Seedlings Growth under Different Conditions

The endogenous pool of phytoregulators in plant tissues supplied with microbial secondary metabolites may be crucial for the development of winter wheat seedlings during cool springs. The phytohormones may be synthesized by psychrotrophic microorganisms in lower temperatures occurring in a temperate climate. Two fungal isolates from the Spitzbergen soils after the microscopic observations and “the internal transcribed spacer” (ITS) region molecular characterization were identified as Mortierella antarctica (MA DEM7) and Mortierella verticillata (MV DEM32). In order to study the synthesis of indoleacetic acid (IAA) and gibberellic acid (GA), Mortierella strains were grown on media supplemented with precursor of phytohormones tryptophan at 9, 15 °C, and 20 °C for nine days. The highest amount of IAA synthesis was identified in MV DEM32 nine-day-culture at 15 °C with 1.5 mM of tryptophan. At the same temperature (15 °C), the significant promoting effect (about 40% root and shoot fresh weight) of this strain on seedlings was observed. However, only MA DEM-7 had the ACC (1-aminocyclopropane-1-carboxylate) deaminase activity with the highest efficiency at 9 °C and synthesized IAA without tryptophan. Moreover, at the same conditions, the strain was confirmed to possess the strong promoting effect (about 40% root and 24% shoot fresh weight) on seedlings. Both strains synthesized GA in all tested terms and temperatures. The studied Mortierella strains had some important traits that led them to be considered as microbial biofertilizers components, improving plant growth in difficult temperate climates.

Enhancement of growth and salt tolerance of rice seedlings by ACC deaminase-producing Burkholderia sp. MTCC 12259

Increasing soil salinity is often associated with accelerated ethylene production in plants, leading to overall growth reduction. The salt-tolerant 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing PGPR may alleviate salt stress by reducing the production of stress ethylene. In this study, a salt-tolerant ACC deaminase-producing strain named P50 was isolated from a coastal rice field in Odisha, India, which enhanced the growth of rice seedlings under salt stress. The P50 strain was identified as Burkholderia sp. based on phenotypic characteristics, MALDI-TOF MS data for ribosomal proteins and 16S rDNA sequence-based homology. Various PGP traits of strain P50 were characterized, among which the ACC deaminase activity was optimized at different physical conditions and confirmed by enzyme assay, as well as FTIR. The IAA, EPS and proline production of this strain were estimated under increasing NaCl concentrations essential for plant growth promotion under salt stress. Finally, the P50 strain was utilized in a gnotobiotic assay using rice seedlings (cv. Swarnamasuri) under saline stress. Seedlings treated with the P50 strain showed improvement in various morphological and biochemical characteristics, ROS scavenging antioxidant enzymatic activities, and reduced amounts of stress ethylene compared to non-inoculated strains under salinity. In addition, isolation of the ACC deaminase mutant of this strain was not found to reduce stress ethylene, confirming that the P50 strain was associated with a reduction in stress ethylene. Strain P50 was also found to colonize the root surfaces of rice seedlings associated with the plant-microbe interaction process. Thus, as an effective salt-tolerant PGPR, strain P50 can be utilized in salt-affected agricultural fields to improve plant growth in a sustainable manner.

Priming with ACC-utilizing bacterium attenuated copper toxicity, improved oxidative stress tolerance, and increased phytoextraction capacity in wheat.

The major challenges for the plants growing in metal-contaminated soils are deficiency of nutrients, biomass reduction, and severe oxidative damages in the presence of heavy metals. In this regard, our aim was to overcome these challenges through the use of efficient microbial strains in metal-polluted soils and to assess its/their physiological and biochemical effects. In the current study, a copper (Cu)-resistant bacterium was isolated from the rhizospheric soil of 'Ziziphus nummularia' and evaluated for its ability to promote the wheat growth under the gradient stress of copper. Based on 16S rRNA gene sequencing, the isolate was identified as Pantoea sp. Among the plant growth promoting tests, the isolate showed the production of indole acetic acid, solubilization of inorganic phosphate, and ACC deaminase activity. Also, the isolate showed resistance to many heavy metals and antibiotics and increased the water-soluble copper in solution. The results of pot studies showed that bacterial application promoted various growth parameters of wheat plants and also enhanced the Cu uptake of wheat from the Cu-amended soil. The results showed that enhancement of Cu stress (100 to 300mgkg-1) resulted in a decrease in various compatible solutes such as proline, total soluble sugars, and total protein content, and increase in the level of malondialdehyde (MDA), latter of which is the indicator of oxidative stress. Bacterial treatment markedly increased the proline, soluble sugar, total protein content, and decreased the MDA content under Cu stress. In addition, bacterial inoculation significantly alleviated the harmful effect of metal toxicity by decreasing the activation of ROS molecules including superoxide (O2-) and hydrogen peroxide (H2O2). The activation of various antioxidative enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) was noted following bacterial inoculation under Cu stress. Therefore, the present study demonstrates the potential of the isolate Pantoea sp. ZNP-5 to improve the growth and phytoextraction of metal from the metal-polluted soil through the polyphasic mechanism of action.

Bacterial ACC Deaminase Activity in Promoting Plant Growth on Areas Contaminated with Heavy Metals

Bacterial ACC Deaminase Activity in Promoting Plant Growth on Areas Contaminated with Heavy Metals

Plant growth promoting rhizobacteria with ACC deaminase activity isolated from Mediterranean dryland areas in Chile: Effects on early nodulation in alfalfa

Plant growth promoting rhizobacteria with ACC deaminase activity isolated from Mediterranean dryland areas in Chile: Effects on early nodulation in alfalfa

Enhancement of alfalfa yield and quality by plant growth-promoting rhizobacteria under saline-alkali conditions.

Bacteria with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity could decrease the ethylene level, confer resistance of plant, and stimulate plant growth under biotic and abiotic stress conditions. Plant growth-promoting rhizobacteria (PGPR) strains Enterobacter aerogenes (LJL-5) and Pseudomonas aeruginosa (LJL-13) were obtained from the rhizosphere of alfalfa grown under saline-alkali conditions. The ACC deaminase activity of E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) was approximately 2-5 µmol mg-1 h-1 . indole acetic acid synthesis was increased with the increasing concentration of l-tryptophan. Siderophore production and phosphate solubilization in Ps. aeruginosa (LJL-13) were higher than those in E. aerogenes (LJL-5). Compared to the non-inoculated seedlings (1.31 ng mL-1 h-1 ), inoculated alfalfa seedlings with E. aerogenes (LJL-5) (0.90 ng mL-1 h-1 ) and Ps. aeruginosa (LJL-13) (0.78 ng mL-1 h-1 ) emitted lower levels of ethylene. Under saline-alkali conditions in the greenhouse, inoculation with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) increased the biomass, soil and plant analyzer development (SPAD), and P content of alfalfa plants, and also induced the activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase), promoted the accumulation of antioxidant substances and removed various harmful substances. Under saline-alkali conditions in the field (2012, 2013, and 2014), inoculation of alfalfa with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) significantly increased the shoot height, fresh and dry weights, yield and crude protein content of alfalfa plants, but decreased the fiber content. Two PGPR strains were isolated from the rhizosphere of alfalfa in saline-alkali conditions. Both strains could promote alfalfa growth in saline-alkali soil, and could be used as biofertilizer to promote plant growth under stress and reduce environmental pollution caused by fertilizers simultaneously. © 2018 Society of Chemical Industry.