Rhizobacterial Strains Research Articles

Lead-Resistant Morganella morganii Rhizobacteria Reduced Lead Toxicity in Arabidopsis thaliana by Improving Growth, Physiology, and Antioxidant Activities

Biological remediation serves as a powerful technique for addressing heavy metals toxicity in metals-contaminated soils. The present study aimed to evaluate the efficacy of lead (Pb)-resistant rhizobacterial strains on growth, photosynthetic traits, and antioxidant activities of the Arabidopsis plant under lead toxicity in pot conditions. Two pre-isolated and pre-characterized Pb-resistant Morganella morganii (ABT3) and Morganella morganii (ABT9) strains were used for inoculating Arabidopsis plants grown under varying Pb concentrations (1.5 mM and 2.5 mM) using PbNO3 as the lead source. The treatments were set up in a completely randomized design with four replications. Data on growth parameters, physiological characteristics, lipid peroxidation, and antioxidant activities were recorded at harvesting. It was observed that Pb contamination caused a significant reduction in Arabidopsis growth, chlorophyll content and quantum yield at both lead concentrations. The Pb concentration of 2.5 mM, showed a substantial decrease in all parameters, including shoot fresh weight (58.72%), shoot dry weight (59.31%), root fresh weight (67.31%), root dry weight (67.28%), chlorophyll content (48.69%), quantum yield (62.36%), catalase activity (65.30%), superoxide dismutase (60.88%), and peroxidase activity (60.54%) while increasing lipid peroxidation (113.8%). However, the inoculation with Pb-resistant M. morganii strains (ABT3 and ABT9) improved plant growth, photosynthesis and antioxidant activities, while reduced the malondialdehyde content of Arabidopsis compared to control plants without inoculation. The M. morganii strain ABT9 showed a maximum increase in the shoot fresh weight (67.18%), shoot dry weight (67.96%), root fresh weight (94.04%), root dry weight (93.92%), shoot length (148.88%), root length (123.33%), chlorophyll content (52.53%), quantum yield (58.57%), catalase activity (39.46%), superoxide dismutase (21.84%), and peroxidase activity (22.34%) while decreasing lipid peroxidation (35.28%). PCA analysis further showed that all nine treatments scattered differently across the PC1 and PC2, having 81.4% and 17.0% data variance, respectively, indicating the efficiency of Pb-resistant strains. The heatmap further validated that the introduction of Pb-resistant strains positively correlated with the growth parameters, quantum yield, chlorophyll content and antioxidant activities of Arabidopsis seedlings. Both Pb-resistant strains improved Arabidopsis plant growth and photosynthetic efficiency under lead stress conditions. Thus, both Morganella morganii ABT3 and Morganella morganii ABT9 strains can be considered as bio-fertilizer for reducing lead toxicity thereby improving plant growth and physiology in metal-contaminated agricultural soils.

Improved salinity and dust stress tolerance in the desert halophyte Haloxylon aphyllum by halotolerant plant growth-promoting rhizobacteria.

Because of global warming, desertification is increasing. One of the best strategies for combating desertification is reforestation of forests and biological operations of vegetation. However, events like soil salinity and dust storms, as the most important manifestations of desertification, prevent vegetation from settling in these areas. In this study, the effects of two halotolerant plant growth-promoting rhizobacterial strains, Bacillus pumilus HR and Zhihengliuella halotolerans SB, on physiological and nutritional status of the desert halophyte Haloxylon aphyllum under the stress of salinity (0, 300, and 600 mM NaCl) and dust (0 and 1.5 g m−2 month−1) were examined. Under dust application, the Z. halotolerans SB strain compared to the B. pumilus HR strain and the combination of these two bacterial strains improved the content of total chlorophyll (247 and 316%), carotenoid (94 and 107%), phosphorus (113 and 209%), magnesium (196 and 212%), and total dry biomass (13 and 28%) in H. aphyllum at salinity levels of 300 and 600 mM NaCl, respectively. Under conditions of combined application of dust and salinity, B. pumilus HR compared to Z. halotolerans SB and the combination of two strains at salinity levels of 300 and 600 mM NaCl, respectively, had better performance in increasing the content of iron (53 and 69%), calcium (38 and 161%), and seedling quality index (95 and 56%) in H. aphyllum. The results also showed that both bacterial strains and their combination were able to reduce the content of ascorbic acid, flavonoid, total phenol, proline, and malondialdehyde, and catalase activity, and ultimately improve the antioxidant capacity of H. aphyllum. This showed that the use of halotolerant rhizobacteria can stop the production of free radicals and thus prevent cell membrane damage and the formation of malondialdehyde under salinity and dust stress. The results of this study for the first time showed that halotolerant rhizobacteria can increase the seedling quality index of H. aphyllum under combined conditions of salinity and dust. The use of these bacteria can be useful in the optimal afforestation of H. aphyllum species in arid and semi-arid ecosystems.

Effects of multiple halotolerant rhizobacteria on the tolerance, growth, and yield of rice plants under salt stress.

Halotolerant bacteria get adapted to a saline environment through modified physiological/structural characteristics and may provide stress tolerance along with enhanced growth to the host plants by different direct and indirect mechanisms. This study reports on multiple halotolerant plant growth-promoting rhizobacteria isolated from the coastal soils in Bangladesh, in fields where the halophytic wild rice Oryza coarctata is endemic. The aim was to find halotolerant bacteria for potential use as biofertilizer under normal/salt-stressed conditions. In this study, eight different strains were selected from a total of 20 rhizobacterial isolates from the saline-prone regions of Debhata and Satkhira based on their higher salt tolerance. 16S rRNA gene sequencing results of the rhizobacterial strains revealed that they belonged to Halobacillus, Bacillus, Acinetobactor, and Enterobactor genera. A total of ten halotolerant rhizobacteria (the other 2 bacteria were previously isolated and already reported as beneficial for rice growth) were used as both single inoculants and in combinations and applied to rice growing in pots. To investigate their capability to improve rice growth, physiological parameters such as shoot and root length and weight, chlorophyll content at the seedling stage as well as survival and yield at the reproductive stage were measured in the absence or presence (in concentration 40 or 80 mmol/L) of NaCl and in the absence or presence of the rhizobacteria. At the reproductive stage, only 50% of the uninoculated plants survived without setting any grains in 80 mmol/L NaCl in contrast to 100% survival of the rice plants inoculated with a combination of the rhizobacteria. The combined halotolerant rhizobacterial inoculations showed significantly higher chlorophyll retention as well as yield under the maximum NaCl concentration applied compared to application of single species. Thus, the use of a combination of halotolerant rhizobacteria as bioinoculants for rice plants under moderate salinity can synergistically alleviate the effects of stress and promote rice growth and yield.

Amelioration of Organic Carbon and Physical Health of Structurally Disturbed Soil through Microbe–Manure Amalgam

Less precipitation, high temperature, and minimal natural vegetation are characteristic of regions having an arid climate. The harsh environment massively destructs the soil structure of that area by burning soil organic carbon, leading to deteriorated soil nutritional quality, creating a significant threat to agricultural production and food security. Direct application of organic wastes not only substitutes lost organic carbon but also restores soil structure and fertility. This study was conducted to assess the impact of organic amendments, i.e., farm manure (FM), poultry manure (PM), molasses (MO), and Exo-Poly Saccharides (EPS) producing rhizobacterial strains i.e., M2, M19, M22 amalgams as treatments. To assess the impact of treatments on soil carbon and structure restoration to hold more water and nutrients, a 42-day incubation experiment using a completely randomized design (CRD) under the two-factor factorial arrangement was conducted. Macro aggregation (0.25 to >1 mm), carbon retention in macro aggregates, active carbon (dissolved organic carbon, a mineral-associated organic carbon, microbial biomass carbon), total organic carbon, the carbon mineralization activities, and water retention capacities were observed to be highest in soils that were treated with (FM + M2, FM + M22, PM + M19, and MO + M19). Finally, we conclude that organics mineralization by microbial actions releases organic glues that not only impart particle aggregation but also conserve organics as aggregate entrapped carbon. Amalgamated application of microbe–manure combinations directly impacts soil structure and organic carbon contents, but in an indirect scenario, it improves the fertility and productivity of the soil. Therefore, it is strongly recommended to use organic manures and microbes in combination to restore structurally degraded lands.

PGPR improve physiological and yield attributes in mustard under different regimes of water supply

ABSTRACT Study was aimed to evaluate the effect of rhizobacteria on physiological attributes, agro-morphological-traits and yield of mustard under rainfed, one irrigation and two irrigation, at two different agro-climatic locations. At both locations, plant height, yield and physiological attributes – relative water content, membrane stability index and chlorophyll content – were adversely affected under rainfed condition; single irrigation had beneficial effect on these parameters. Two irrigations did not have similar impact at both locations. Inoculation with all the rhizobacteria improved yield, yield components and most of the assayed physiological attributes. The highest seed yield at Location I (2410 kg ha−1) and Location II (2130 kg ha−1) was obtained due to the inoculation with rhizobacteria Bacillus casamancensis MKS 6 and Bacillus sp. MRD 17, respectively; there was an increase in mustard seed yield by 650 kg ha−1 and 430 kg ha−1 compared with uninoculated treatment at Locations I and II, respectively. Correlation analysis indicated strong positive correlation between most of the plant biometric traits and plant physiological attributes. Hence, due to the application of rhizobacteria, plantphysiological attributes were improved, as a result, crop growth and yield were enhanced. Thus, these rhizobacterial strains can be used as bioinoculants to alleviate the adverse effects of drought and improve crop productivity.

Halotolerant rhizobacteria enhance the tolerance of the desert halophyte Nitraria schoberi to salinity and dust pollution by improving its physiological and nutritional status

Playas have a high potential for producing dust, sand, and salt storms, which can influence human health and agricultural land in the near future. Growing vegetation is an effective way to control wind erosion, but events like soil salinity and dust storms prevent vegetation from settling in these areas. In this study, the effects of two halotolerant plant growth-promoting rhizobacterial strains, Bacillus pumilus HR and Zhihengliuella halotolerans SB, on morpho-physiological and nutritional status of the desert halophyte Nitraria schoberi under the stress of salinity (0, 300, and 600 mM NaCl) and dust (0 and 1.5 g m−2 month−1) were examined. The results showed that salinity, dust and the combination of the two stresses had a negative effect on most morphological and physiological traits of the plant. Salinity stress reduced potassium, iron, and manganese of N. schoberi by 28, 30, and 21 %, and increased anthocyanins, proline, and peroxidase by 21, 92, and 16 %, respectively. Both bacterial strains and their combination improved plant growth against such stresses. The effect of B. pumilus HR strain was more than that of Z. halotolerans SB strain on the plant. HR strain and SB strain increased chlorophyll a by 62 and 25 %, total dry biomass by 66 and 31 % at 300 mM NaCl level, respectively, and significantly increased seedling quality index by 72 and 76 %, respectively, under dust stress. The results of principal component analysis (PCA) showed that the presence of bacterial strains decreased antioxidant compounds (negative correlation) and increased mineral elements, chlorophyll, total dry biomass, and seedling quality index. This information can help us in the optimal afforestation of this plant species and the fixation of salt dust in the playa under the conditions of climate change in arid and semi-arid ecosystems.

A Combined Use of Rhizobacteria and Moringa Leaf Extract Mitigates the Adverse Effects of Drought Stress in Wheat (Triticum aestivum L.).

Less nutrient availability and drought stress are some serious concerns of agriculture. Both biotic and abiotic stress factors have the potential to limit crop productivity. However, several organic extracts obtained from moringa leaves may induce immunity in plants under nutritional and drought stress for increasing their survival. Additionally, some rhizobacterial strains have the ability to enhance root growth for better nutrient and water uptake in stress conditions. To cover the knowledge gap on the interactive effects of beneficial rhizobacteria and moringa leaf extracts (MLEs), this study was conducted. The aim of this experimental study was to investigate the effectiveness of sole and combined use of rhizobacteria and MLEs against nutritional and drought stress in wheat. Nitrogen-fixing bacteria Pseudomonas aeruginosa (Pa) (108 CFU ml–1) was inoculated to wheat plants with and without foliar-applied MLEs at two different concentrations (MLE 1 = 1:15 v/v and MLE 2 = 1:30 v/v) twice at 25 and 35 days after seed sowing (50 ml per plant) after the establishment of drought stress. Results revealed that Pa + MLE 2 significantly increased fresh weight (FW), dry weight (DW), lengths of roots and shoot and photosynthetic contents of wheat. A significant enhancement in total soluble sugars, total soluble proteins, calcium, potassium, phosphate, and nitrate contents validated the efficacious effect of Pa + MLE 2 over control-treated plants. Significant decrease in sodium, proline, glycine betaine, electrolyte leakage, malondialdehyde, hydrogen peroxide, superoxide dismutase (SOD), and peroxide (POD) concentrations in wheat cultivated under drought stress conditions also represents the imperative role of Pa + MLE 2 over control. In conclusion, Pa + MLE 2 can alleviate nutritional stress and drought effects in wheat. More research in this field is required to proclaim Pa + MLE 2 as the most effective amendment against drought stress in distinct agroecological zones, different soil types, and contrasting wheat cultivars worldwide.

Assessing the potentials of bacterial antagonists for plant growth promotion, nutrient acquisition, and biological control of Southern blight disease in tomato.

Southern blight of tomato caused by Sclerotium rolfsii can cause severe plant mortality and yield losses. The use of rhizobacteria for the biological control of Southern blight disease is a potent alternative to chemical fungicides. Although rhizobacteria are prolific candidates, comprehensive reports regarding their use in tomato disease management are limited. The present study screened six rhizobacterial strains for antagonism against S. rolfsii in dual culture and culture filtrate assays. The selected promising strains were tested further for plant-growth-promoting and biocontrol potentials under in vitro, greenhouse, and field conditions. Of the six strains screened, Stenotrophomonas maltophilia PPB3 and Bacillus subtilis PPB9 showed the superior performance displaying the highest antagonism against S. rolfsii in dual culture (PPB3 88% and PPB9 71% inhibition), and culture filtrate assays (PPB3 53-100% and PPB9 54-100% inhibition at various concentrations). Oxalic acid produced by S. rolfsii was significantly inhibited by both rhizobacteria and supported their growth as a carbon source. The strains produced hydrogen cyanide, chitinases, siderophores, biofilm, and indole acetic acid. They showed the potential to solubilize phosphate and fix nitrogen. Seed treatment with S. maltophilia PPB3 and B. subtilis PPB9 improved seed germination and tomato seedling vigour. Significant increases in plant growth, chlorophyll contents, and N, P, and K concentrations were attained in bacterized plants compared to non-treated controls. The application of antagonists on container-grown seedlings in a greenhouse environment and field-grown tomato plants reduced symptoms of damping-off and Southern blight. The sclerotial counts decreased significantly in these soils. Bacteria-inoculated plants had a higher yield than those in the non-treated control. Bacteria colonized the entire roots, and their populations increased significantly in the protected plants. The results show the potential capabilities of S. maltophilia PPB3 and B. subtilis PPB9 for growth promotion, nutrient acquisition, and biocontrol of southern blight disease in tomatoes.

The impact of plant-associated rhizobacteria on germination capacity, growth and productivity of spring field mustard and emmer wheat

The paper reports the results of field experiments that analysed changes in germination capacity, growth indicators and productivity of two crops in response to seed inoculation: field mustard (Brassica campestris L.) of the Vostochnaya variety (k-274) and emmer wheat (Triticum dicoccum subsp. asiaticum Vavilov) of k-7516 variety. Morphometric parameters and productivity of dry mass were measured during the major stages of crop development. The seeds of field mustard were inoculated with the following bacterial products: Mizorin (Arthrobacter mysorens, strain 7), Mobilin (Pseudomonas fluorescens, strain PG-5) and Flavobakterin (Flavobacterium sp., strain 30). The seeds of emmer wheat were inoculated with Psevdomonas (Pseudomonas fluorescens, strain PG-5) and Rizoagrin (Agrobacterium radiobacter, strain 204). In addition, we also tested biinoculation (combined use of two bacterial products) for each crop. The study aimed to analyse changes in growth indicators and productivity of field mustard and emmer wheat in response to mono- and biinoculation of seeds with plant-associated rhizobacteria. The experiments showed that the application of bacterial products and increasing doses of mineral nitrogen has a stimulating effect on plants. The study proved monoinoculation to be more effective than biinoculation. This may be due to the competing effect of rhizobacterial strains from different bacterial products once the biinoculated seeds are put in soil.

Inducing Drought Tolerance in Wheat through Exopolysaccharide-Producing Rhizobacteria

Wheat is the main staple food in the world, so it is the backbone of food security. Drought not only affects growth and development but also ultimately has a severe impact on the overall productivity of crop plants. Some bacteria are capable of producing exopolysaccharides (EPS) as a survival mechanism, along with other metabolites, which help them survive in stressful conditions. The present study was conducted with the aim of inducing drought stress tolerance in wheat through EPS-producing plant growth-promoting rhizobacteria (PGPR). In this regard, a series of laboratory bioassays were conducted with the aim to isolating, characterizing, and screening the EPS-producing PGPR capable of improving wheat growth under limited water conditions. Thirty rhizobacterial strains (LEW1–LEW30) were isolated from the rhizosphere of wheat. Ten isolates with EPS-producing ability were quantitatively tested for EPS production and IAA production ability. Four of the most efficient EPS-producing strains (LEW3, LEW9, LEW16, and LEW28) were evaluated for their drought tolerance ability along with quantitative production of EPS and IAA under polyethylene glycol (PEG-6000)-induced drought stress. The jar experiment was conducted under gnotobiotic conditions to examine the drought-tolerant wheat genotypes, and two wheat varieties (Johar-16, and Gold-16) were selected for further experiments. The selected varieties were inoculated with EPS-producing rhizobacterial strains and grown under control conditions at different stress levels (0, 2, 4, and 6% PEG-6000). The strain LEW16 showed better results for improving root morphology and seedling growth in both varieties. The maximum increase in germination, growth parameters, percentage, root diameter, root surface area, and root colonization was recorded in Johar-16 by inoculating LEW16 at 6% PEG-6000. Plant growth-promoting traits were tested on the top-performing strains (LEW3, LEW9, and LEW16). Through 16S rRNA sequencing, these strains were identified as Chryseobacterium sp. (LEW3), Acinetobacter sp. (LEW9), and Klebsiella sp. (LEW16), and they showed positive results for phosphorous and zinc solubilization as well as hydrogen cyanide (HCN) production. The partial sequencing results were submitted to the National Center for Biotechnology Information (NCBI) under the accession numbers MW829776, MW829777, and MW829778. These strains are recommended for their evaluation as potential bioinoculants for inducing drought stress tolerance in wheat.

Molecular Identification and Characterization of Plant Growth Promoting Rhizobacteria and their Effect on Seed Germination and Vigour Index of Barley (Hordeum vulgare L.)

Plant growth promoting rhizobacteria (PGPR) are a group of useful bacteria that colonize the plant roots and significantly enhances the plant growth promotion. Keeping this in mind, an investigation was performed for the screening of potent PGPR strains for enhancing seed germination and vigour index of Hordeum vulgare (commonly called barley). Rhizobacterial strains were isolated and screened for various plant growth promoting traits, their effect on seed germination and vigour index of barley plant through pot trial, and resistant ability under various temperature and pH range. Based upon 16S rRNA sequencing data, Pseudomonas punonensis LMT03 (R1), Pseudomonas plecoglossicida R4, Pseudomonas aeruginosa DSM50071 (R2) and Alcaligenes faecalis (DBHU5) isolates were selected and showed positive result for IAA production, Phosphate solubilization, ammonia production, catalase activity, siderophore production and MR-VP test. Barley plants treated with P. punonensis and P. plecoglossicida both showed 94.44% of highest seed germination %, while P. aeruginosa and A. faecalis showed 83.11% and 77.33% respectively in comparison to the control plant shows which 49.99% seed germination only. These respective isolates also showed 2.57, 2.37, 2.0 and 1.69 fold of increase in vigour index as compare to the control plants. The above increase in fold in vigour index and seed germination is much higher as compared to earlier reports. Collectively, the data of current study underpin that addition of these PGPRs to barley rhizosphere appears a promising strategy to enhance root and shoot biomass of this important agriculture crop. To the best of our knowledge this is the first report demonstrating the effect of P. punonensis and P. plecoglossicda on barley crop.

Isolation and Characterization of Phosphate Solubilizing Bacteria and Effect of Growth and Nutrient Uptake of Maize Under Pot and Field Conditions

ABSTRACT Phosphorus deficiency is one of the main factors for limiting agricultural production. The use of Phosphate Soluble Bacteria (PSB) is an environmentally friendly solution to eliminate phosphorus deficiency. Isolation of PSB and determination of plant growth effects of maize were aimed at this study. For this purpose, 62 phosphate solubilizing rhizobacterial strains isolated from soil and the phosphate solubilization abilities of isolates were determined by laboratory, pot, and field trials. After laboratory trials with 62 strains, pot tests were established with 10 isolates. Inoculation of phosphorus PSB was increased plant height19.38–54.25% and plant dry weight12.32–67.63% under pot experiments. Field trials were conducted between 2014 and 2016 with two PSB (S. marcensens and P. brenneri) according to pot experiments. S. marcensens and P. brenneri increased yield of maize32–33% in 2014 and28–25% in 2015, respectively. Application of P. brenneri increased leaf P, K, and Mg content by 13%, 5%, 9%, and S. marcensens increased the same by 10%, 6%, 17%, respectively. P. brenneri and S. marcensens can be used as biological fertilizers as a promising and sustainable approach to maize productivity in P deficient soils.

Native Heavy Metal-Tolerant Plant Growth Promoting Rhizobacteria Improves Sulla spinosissima (L.) Growth in Post-Mining Contaminated Soils.

The potential of rhizobacteria in assisting plants used in the phytostabilization or re-vegetation of soils contaminated by heavy metals is gaining interest all around the world. In this context, six rhizobacterial strains isolated from highly heavy metal-contaminated soils situated in abandoned mining sites around the Oujda region (Morocco) were tested with Sulla spinosissima (L.), a native leguminous plant expanding in this area. The strains used were multi-resistant to heavy metals and possessed multiple plant growth-promoting traits. Potential beneficial effects of the strains were also evaluated in planta by measuring various growth and physiological parameters of inoculated Sulla plants grown in sterilized sand. Inoculation with the Rhodococcus qingshengii strain LMR340 boosted plant biomass (39% to 83% increase compared to uninoculated plants), chlorophyll and carotenoid content (up to 29%), and antioxidant enzyme activities (15% to 80% increase). Based on these interesting findings, selected strains were inoculated into plants growing in a heavy metal, multi-polluted, and poor soil. Under these conditions, non-inoculated plants and those inoculated with the strain LMR250 were unable to grow, while the other five bacterial inoculants restored plant growth. The best performing strain, Pseudarthrobacter oxydans LMR291, could be considered as a good biofertilizer and/or biostimulant candidate to be used for promoting the growth of selected plants in re-vegetation and/or phytostabilization programs of degraded and contaminated soils.

Iron biofortification potential of siderophore producing rhizobacterial strains for improving growth, yield and iron contents of groundnut

Biofortification in crops is an effective and sustainable approach to reduce global malnutrition. Groundnut (Arachis hypogea L.) is inherently low in micronutrients, especially iron. A greenhouse study was conducted to evaluate the effect of siderophore producing bacterial strains (SPBs) on growth, yield and iron content of groundnut. Three efficient SPBs identified as Bacillus subtilis and their consortia were used alone and with soil or foliar applied iron. The results revealed that the inoculation of SPBs alone and combination with soil applied Fe, showed maximum relative increase of 63 and 86 percent in shoot fresh and dry weight respectively. Likewise, the number of pods plant−1, pod weight plant−1, 20 pod length and 100 kernel weight of groundnut were increased significantly in response to sole application SPBs and their combinations with soil applied (SA) or foliar applied (FA) iron. Moreover, nutrient (N, P, K, Zn & Fe) concentrations in kernel and straw were also showed significant differences in all treatments. Findings further revealed that the combined application of SPBs + Fe-SA increased total Fe-uptake of groundnut between 24.14 to 49.75 percent while for SPBs + Fe-FA treatment this increase varied between 14.73 to 45.72 percent (over to the SPBs alone) The overall results indicated that SPBs have the potential to increase growth, yield and nutrient contents of groundnut which advocate that microbial-mediated Fe biofortification of groundnut could be a promising strategy to ameliorate Fe deficiency-induced disordering in human beings especially in developing countries.

New rhizobacteria strains with effective antimycotic compounds against rhizome rot pathogens and identification of genes encoding antimicrobial peptides

Bacterial strains were isolated from turmeric rhizosphere and 18 of them exhibited plant growth promoting traits and ability to solubilize mineral. They also showed the ability to concurrently suppress the growth of multiple fungal phytopathogens under in vitro assay. An isolate of Bacillus safensis, produced indole 3-acetic acid, NH3, HCN, siderophore, and cell wall degrading enzymes (cellulase, protease and pectinase) and exhibited remarkable suppression of various fungal pathogens infecting turmeric viz., Pythium myriotylum, P. aphanidermatum, Colletotrichum gloeosporioides, C. capsici, Macrophomina phaseolina and Fusarium oxysporum under in vitro conditions. In a subsequent greenhouse experiment, turmeric was inoculated with these fungal pathogens and in treatments with B. safensis the Disease Index (DI) was significantly reduced compared to the fungicide treatment. The greenhouse trials evidently demonstrated that the rhizome rot incidence in turmeric treated with B. safensis decreased by 84.61%, compared to fungicide treatments. We searched for the presence of biosynthetic genes that encode for the production of antimicrobial peptides (AMP) in the shortlisted rhizobacterial strains and the B. safensis strain, with the most biocontrol efficiency showed the presence of the genes encoding bacillomycin, surfactin and iturin. The dominance of putatively encoded biosynthetic genes reaffirmed the robust biocontrol potential of this strain for protection against a broad array of fungal phytopathogens. Our findings indicated that the growth promotional and antifungal potential of B. safensis strain, IISR-TB4 (NCBI- MT192800) could be further exploited to reduce the dependence on fungicides for sustainable turmeric cultivation.

Effects of plant growth-promoting rhizobacteria on uptake and utilization of phosphorus and root architecture in apple seedlings under water limited regimes

The aim of this research was to examine the relationships among Pseudomonas fluorescens (YX2) plant growth promoting rhizobacteria (PGPR), phosphorus (P) absorption by plants, and root system architecture in apple seedlings exposed to mild, moderate or severe drought stresses. All the treatments were divided into two groups: 1) inoculated with a plant rhizobacterial strain (YX2), and 2) the non-inoculated control. Under drought stress, the YX2 inoculation improved root growth, root activity by 6%, and uptake of P, thereby promoting apple seedling growth along with the dry weight of above-ground plant parts in the mild and moderate water stress regimes. Furthermore, the inoculation also promoted total P contents in plants under both mild and moderate drought stresses. Overall, application of Pseudomonas fluorescens (YX2) is a promising approach to enhance apple production in agricultural production systems.

Bradyrhizobium japonicum IRAT FA3 Alters Arabidopsis thaliana Root Architecture via Regulation of Auxin Efflux Transporters PIN2, PIN3, PIN7, and ABCB19.

Beneficial rhizobacteria can stimulate changes in plant root development. Although root system growth is mediated by multiple factors, the regulated distribution of the phytohormone auxin within root tissues plays a principal role. Auxin transport facilitators help to generate the auxin gradients and maxima that determine root structure. Here, we show that the plant-growth-promoting rhizobacterial strain Bradyrhizobium japonicum IRAT FA3 influences specific auxin efflux transporters to alter Arabidopsis thaliana root morphology. Gene expression profiling of host transcripts in control and B. japonicum-inoculated roots of the wild-type A. thaliana accession Col-0 confirmed upregulation of PIN2, PIN3, PIN7, and ABCB19 with B. japonicum and identified genes potentially contributing to a diverse array of auxin-related responses. Cocultivation of the bacterium with loss-of-function auxin efflux transport mutants revealed that B. japonicum requires PIN3, PIN7, and ABCB19 to increase lateral root development and utilizes PIN2 to reduce primary root length. Accelerated lateral root primordia production due to B. japonicum was not observed in single pin3, pin7, or abcb19 mutants, suggesting independent roles for PIN3, PIN7, and ABCB19 during the plant-microbe interaction. Our work demonstrates B. japonicum's influence over host transcriptional reprogramming during plant interaction with this beneficial microbe and the subsequent alterations to root system architecture.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Combined Use of Novel Endophytic and Rhizobacterial Strains Upregulates Antioxidant Enzyme Systems and Mineral Accumulation in Wheat

Wheat is the third largest grown crop after maize and rice worldwide. Integrated use of chemical and biofertilizers have the potential to improve crop yield and quality due to their growth-promoting attributes. Therefore, the present study planned to evaluate the effectiveness of endophytic (Paenibacillus sp. strain (ZE11), Bacillus subtilis (ZE15) and Bacillus megaterium (ZE32)) and rhizobacterial strains (Bacillus subtilis (ZR2) Bacillus subtilis (ZR3) and Bacillus megaterium strain (ZR19)), solely and in combination, to increase the productivity of wheat and microbial activity in the rhizosphere. The maximum increase in microbial biomass carbon (44%), available phosphorous (30%), ammonium–nitrogen (24%), nitrate–nitrogen (37%), iron (10%), zinc (11%) and bacterial population (31%) was recorded by co-inoculation of ZE11 + ZR3. Subsequently, co-inoculation of ZE11+ZR3 showed a maximum increase of 31%, 29%, 30%, 27%, 33%, 30%, 25%, 9%, 15%, 9%, 18% and 26% in superoxidase dismutase (SOD), peroxidase dismutase (POD), catalase (CAT), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and peroxidase (POX), grain yield, nitrogen, phosphorous, potassium, iron and zinc in grains, respectively, as compared to uninoculated control. The sole inoculation of ZR19 showed maximum harvest index (45.5%). The sole inoculation of endophytes and rhizobacteria has a significant effect on growth, physiology, and wheat crop yield. However, co-inoculation had a better effect and can be used to develop multi-strain biofertilizer to promote growth and yield of crops.

Draft Genome Sequences of Three Identified Rhizobacteria Associated with Maize Rhizosphere.

ABSTRACTIn this study, we sequenced the entire genomes of three identified rhizobacterial strains associated with maize plantation. Genome annotation of the sequenced data revealed several putative growth-promoting proteins associated with the production of indoleacetic acids and siderophore, the assimilation of nitrogen, and phosphorus solubilization.

Exploration, isolation and characterization of indigenous rhizobacteria from patchouli rhizosphere as PGPR candidates in producing IAA and solubilizing phosphate

Microorganisms that are active and aggressive colonizing the rhizosphere are known as rhizobacteria. They are able to act as biofertilizers, bioprotectants, biostimulants and bioremediation. This study aims to identify and characterize groups of rhizobacteria present in the patchouli rhizosphere that can produce IAA compounds and have the ability to solubilize phosphate in the soil. Soil samples were taken from the patchouli rhizosphere at Purwosari Village, Nagan Raya, Aceh Province, Indonesia. This study used quantitative and qualitative descriptive analysis through serial dilutions to obtain rhizobacterial strains. Parameters observed were macroscopic and microscopic characteristics, gram test, IAA production and phosphate solubilization. The study obtained 37 isolates of rhizobacteria from Purwosari (PS), comprising 25 isolates of gram positive and 12 isolates of gram negative. The rhizobacteria PS 5/1 produced the lowest IAA at 21.66 ppm, whereas isolate 5/6 C produced the highest IAA at 83.38 ppm. Twenty-five isolates of rhizobacteria could solubilize phosphate while the remaining 12 isolates did not have this ability. The rhizobacteria PS 7/1 resulted in the highest PSI at 2.55 and isolates PS 8/7 produced the lowest PSI at 1.33. The rhizobacteria isolates that can produce IAA and phosphate solubilizing have the potential to be used as PGPR candidates.