Plant Growth Promoting Rhizobacterial Research Articles

Suppression of tomato bacterial speck disease (Pseudomonas syringae pv. tomato (Okabe) Young, Dye, & Wilkie) via induced systemic resistance by Pseudomonas and Bacillus strains

Bacterial speck Pseudomonas syringae pv. tomato (Pst) (Okabe) Young, Dye, & Wilkie is a widespread disease in tomato plants. Four plant growth-promoting rhizobacterial (PGPR) strains 5(3), 68(2), 36(1), and 47(3) played a significant role (50% and higher) in reducing spot disease severity. Selected strains were identified as Pseudomonas koreensis 5(3), Bacillus mycoides 68(2), Bacillus mojavensis 36(1), and Bacillus simplex 47(3) using the MALDI Biotyper classification system. In planta assay using tomato seedlings were inoculated with the bacterial strains alone or in dual combination. Pseudomonas koreensis 5(3) (51.9%–74.29%) and Bacillus mycoides 68(2) (36.70%–65.56%) both provided a significant reduction in foliar severity caused by bacterial speck disease agent Pseudomonas syringae pv. tomato (Okabe) Young, Dye, & Wilkie. Bacillus simplex 47(3) and Bacillus mojavensis 36(1) were successful only in combined treatments. Defense enzymes Proline, Peroxidase, and Catalase were induced by PGPR strains in comparison with those of control plants. Hydrogen peroxide (H2O2) and callose deposition were evident at reaction sites induced by PGPR strains. The accumulation of callose, H2O2, and high levels of defense enzymes via the treatment of PGPRs might play a significant role in a practical, safe, and effective way to control Pseudomonas syringae pv. tomato.

Bradyrhizobium japonicum IRAT FA3 promotes salt tolerance through jasmonic acid priming in Arabidopsis thaliana

BackgroundPlant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants’ responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress.ResultsThe plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress.ConclusionOur data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance.

Evaluation of compatibility of native plant growth promoting rhizobacterial isolates against chemical pesticides

Conventional agriculture relies heavily on chemical fertilizers, pesticides and weedicides to control plant diseases, pests and weeds to improve production. Consequently, the soil receives the bulk of complex agrochemical compounds many of which are poisonous to the activity of non-target beneficial soil microorganisms. There is a need to check the tolerance of biocontrol agents like Plant Growth Promoting Rhizobacterial (PGPR) to various pesticides before their practical application. Taking this into account, the investigation was conducted for the screening of the PGPR isolates against chemical pesticide degradation potentialities in Plant Bacteriological Laboratory, Department of Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal during 2021-22. All the native rhizobacterial, Bacillus and Fluorescent pseudomonad isolates tested had good potentiality to tolerate Carbendazim and Glyphosate. Among native Bacillus isolates, BRB89, BRB42, PR 19, PR 20, BRB 52, BRB 56, BRB 74, and SM 9 showed moderate tolerance, whereas among all the native Fluorescent pseudomonads, all except GP2 showed high tolerance against Paraquat. All native Bacillus isolates except PR16 were highly sensitive against Chorpyriphos. However, all the native fluorescent pseudomonads showed tolerance against Chorpyriphos even at 2000 ppm concentration.

Single and combined effects of Pythium oligandrum Po37 and a consortium of three rhizobacterial strains on Sclerotinia stem rot severity and tomato growth promotion

Individual plant growth-promoting rhizobacterial (PGPR) strains (Bacillus thuringiensis B2, Bacillus subtilis B10 and Enterobacter cloacae B16) and their combination were used, with or without Pythium oligandrum, against Sclerotinia sclerotiorum. In vitro, all biological control agents (BCAs) reduced successfully hyphal growth of the targeted pathogenic fungus. They displayed antifungal activity by more than 50% compared to controls. In planta trials were conducted two years in the row and led to a significant decrease in stem rot severity two months after the antagonist’s application onto infected tomato plants. The reduction reached 75% using rhizobacterial mixtures and 72% using P. oligandrum alone, compared to controls. The plant growth-promoting potential of the three-strain consortium and P. oligandrum was also assessed. Increased height in disease-free plants was obtained with rhizobacterial mixtures (60%) compared to P. oligandrum (47%). The BCA’s mixture increased the height of treated plants inoculated with S. sclerotiorum (up to 80%) compared to inoculated and untreated plants. The fresh weight of the aerial parts and roots of disease-free plants was increased by 42 and 30% over control following their treatment with mixtures of rhizobacteria and P. oligandrum alone, respectively. On plants inoculated with S. sclerotiorum in both trials, the highest growth-enhancing effect was achieved using the combined treatment based on P. oligandrum and the three-strain rhizobacterial consortium (Po37 + B2 + B10 + B16). The rhizospheric microbial communities were assessed using Single Strand Conformational Polymorphism (SSCP). Differences in the genetic structure of the fungal and bacterial communities were observed following treatments applied in both trials.

Salt-tolerant PGPR strain Priestia endophytica SK1 promotes fenugreek growth under salt stress by inducing nitrogen assimilation and secondary metabolites.

Soil salinity is a huge obstacle in crop production worldwide. Saline soil can reduce active chemical contents in medicinal plants of the Leguminosae family through crippled normal nodule function. Intensive efforts are underway to improve yield and medicinal value of leguminous herbs under salt stress condition by using benign microbes. Here, an attempt was made to explore the salt-tolerant bacteria associated with rhizosphere of fenugreek plant (Trigonella foenum-graecum L.) and to evaluate their impact on host plant growth and metabolite of pharmaceutical importance. A salt-tolerant plant growth promoting rhizobacterial (PGPR) strain Priestia endophytica SK1 isolated from fenugreek rhizospheric soil, which increased biomass and metabolite content in plants grown under saline stress. SK1 bacterial application induced nodule formation and enhanced nitrogen and phosphorus content under salt (100 mM NaCl) stress as compared to control plants. H2 O2 production and lipid peroxidation as a measure of stress were observed high in control plants, while a reduction in these parameters was observed in plants inoculated with SK1. In addition, a significant effect was found on the phenolic compounds and trigonelline content in fenugreek plant inoculated with SK1 bacterium. An increased trigonelline content of about 54% over uninoculated control was recorded under salt stress. The results of this study revealed that the application of salt-tolerant PGPR strain P. endophytica SK1 induced nitrogen fixation machinery that leads to alleviate salt stress and improved the biosynthesis of trigonelline content in fenugreek. This study extends our understanding on the significance of rhizosphere microbiome and their beneficial role in plant health under environmental stress to promote agro-eco-farming practices.

Phytohormones producing rhizobacteria alleviate heavy metals stress in soybean through multilayered response

Aimof the current research was to use plant growth promoting rhizobacteria for sequestration and biotransformation of the toxic form of Cr and As into non-toxic form. Remediating these contaminants using microbes is a common technique and rhizo-microbiota not only relieves metal stress but also acts as biofertilizers. Role of plant growth-promoting rhizobacterial (PGPR) strains Acinetobacter beijerinckii (C5) and Raoultella planticola (C9) in counteracting chromium and arsenic stress in soybean seedlings was assessed. The isolated rhizobacteria were able to tolerate excessive quantities (up to 1200 ppm) of chromate and arsenate in liquid media. Beside their growth in heavy metal containing media, the strains were able to bio-transform chromate and arsenate to their least toxic form. They released significant quantities of stress related metabolites including phenols, flavonoids, proline, sugars and protein even in the presence of 1200 ppm of the heavy metals. They also released several plant hormones together with indole-3-acetic acid (IAA), salicylic acid (SA) and gibberellins. Another important feature of the isolates was their ability to solubilize phosphate and release siderophores and exposure to different levels of the selected heavy metals enhanced phosphate solubilization potential of both the isolates by up to 2-fold. Release of siderophore in A. beijerinckii C5 was enhanced by increasing heavy metals concentration in the media but in case of R. planticola C9 a decline was noted. When inoculated on soybean seedlings, the isolates modulated several metabolites of the hos plant enabling them to combat heavy metal toxicity at different levels. The PGPR strains boosted host’s antioxidants production which minimized the oxidative damage by scavenging excessive ROS produced under stress. Control plants showed upregulation of stress response metabolites compared to PGPR application, whereas, IAA and SA were significantly higher in PGPR associated seedlings. In conclusion, PGPR alters the physiological and metabolic responses of soybean enabling it to cope better with chromate and arsenic toxicity and grow well under the stress.

Potential use of Solanum lycopersicum and plant growth promoting rhizobacterial (PGPR) strains for the phytoremediation of endosulfan stressed soil

This study aimed to assess the role of Solanum lycopersicum and plant growth promoting rhizobacterial (PGPR) strains to remove endosulfan present in the soil. S. lycopersicum was grown in endosulfan amended soil (5, 10, 25, and 50 mg kg−1) inoculated with PGPR strains for 40, 80, and 120 days. The influence of PGPR inoculation on endosulfan accumulation in plant tissues, endosulfan degradation in soil, and plant growth parameters were evaluated. The oxidative stress tolerance was assessed by determining the malondialdehyde formation in S. lycopersicum planted in endosulfan stressed soil inoculated with PGPR strains. The results showed that uptake of endosulfan followed root > shoot pathway in association with a reduction in endosulfan accumulation in inoculated plants as related to un-inoculated plants. Moreover, inoculation of PGPR strains showed a beneficial influence on the degradation of endosulfan, Bacillus sp. PRB101 showed maximum degradation (89% at 5 mg kg−1 of soil) of endosulfan at 120 days after sowing. Furthermore, the content of malondialdehyde was lower in inoculated plants as related to un-inoculated plants. Inoculation of PGPR strains efficiently enhanced plant biomass. The findings showed the effectiveness of PGPR strains to increase the decontamination of endosulfan stressed soil and decline endosulfan concentration in the plant tissues.

Use of plant growth-promoting bacteria to enhance salinity stress in soybean (Glycine max L.) plants.

The effects of three rhizobacterial isolates namely Pseudomonas fluorescens (M1), Pseudomonas putida (M2) and Bacillus subtilis (M3) were examined to enhance growth and chemical components such as chlorophyll and proline of three cultivars of soybean (Glycine max L.) under two levels of salinity stress (S1 = 200 mM and S2 = 400 mM of NaCl salt). Several morphological and physiological parameters were investigated. The highest mean values of final germination percent (FGP) were registered in cultivar Crawford (95%) followed by Giza111 cultivar (93%) in the presence of P. fluorescens, while, FGP of Clark was 85%. Mean germination time was decreased by the application of P. fluorescens or P. putida in both salt stressed and unstressed traits. All growth parameters were significantly decreased by salinity treatments, particularly at S2. A significant increase in stem length and shoot fresh weight was recorded in plants treated with P. fluorescens. This enhancing trend was followed by the application of P. putida then B. subtilis. Chlorophyll contents and plant soluble proteins were decreased, while proline content was increased as compared with control treatment. Results showed that the salt tolerant cultivar, Crawford, may have a better tolerance strategy against oxidative damages by increasing antioxidant enzymes activities under high salinity stress. These results suggest that salt induced oxidative stress in soybean is generally counteracted by enzymatic defense systems stimulated under harsh conditions. Our results showed that inoculation with plant growth-promoting rhizobacterial (PGPR) alleviated the harmful effects of salinity stress on soybean cultivars. The diversity in the phylogenetic relationship and in the level of genetic among cultivars was assessed by SDS-PAGE and RAPD markers. Among the polymorphism bands, only few were found to be useful as positive or negative markers associated with salt stress. The maximum number of bands (17) was recorded in Crawford, while the minimum number of bands (11) was recorded in Clark. Therefore, the ISSR can be used to identify alleles associated with the salt stress in soybean germplasm.

Isolation and characterization of streptomycetes and pseudomonad strains with antagonistic activity against the plant parasitic nematode Pratylenchus penetrans and fungi associated with replant disease

Pratylenchus penetrans is one of the most important plant-parasitic nematodes causing losses in economically significant crops such as apple, cherry, corn, grapes, oat, onion, peach, potato, soybean, strawberry, and wheat. The objective of this study was to isolate and characterize plant growth promoting rhizobacterial (PGPR) strains from sweet cherry rhizospheres with biocontrol potential against P. penetrans, and to evaluate the antagonistic activity of the selected strains on a model plant (onion), in a growth chamber experiment. Five strains: three actinomycetes (Streptomyces fulvissimus A12, S. venezuelae A30, and S. annulatus A34) and two pseudomonads (Pseudomonas sp. P3 and P. donghuensis P17) with nematicidal activity were isolated. The selected PGPR strains decreased P. penetrans populations on onion roots and enhanced onion root length and dry weight. Among possible mechanisms of action, the strains displayed the capacity to produce nematicidal lytic enzymes such as chitinases and proteases, and form biofilms, which is an advantage in colonizing the plant rhizosphere. Some of them also showed antifungal activity against the phytopathogenic fungi Fusarium oxysporum C1-1, Ilyonectria macrodidyma C1-1, and Ilyonectria spp. C2-1 isolated from roots of cherry trees affected by replant disease. The multifunctionality of the strains, and the fact that they were isolated from the cherry rhizosphere, makes them good candidates to be used as biocontrol agents in sweet cherry orchards affected by P. penetrans.

Inorganic Chemical Fertilizer Application to Wheat Reduces the Abundance of Putative Plant Growth-Promoting Rhizobacteria.

The profound negative effect of inorganic chemical fertilizer application on rhizobacterial diversity has been well documented using 16S rRNA gene amplicon sequencing and predictive metagenomics. We aimed to measure the function and relative abundance of readily culturable putative plant growth-promoting rhizobacterial (PGPR) isolates from wheat root soil samples under contrasting inorganic fertilization regimes. We hypothesized that putative PGPR abundance will be reduced in fertilized relative to unfertilized samples. Triticum aestivum cv. Cadenza seeds were sown in a nutrient depleted agricultural soil in pots treated with and without Osmocote® fertilizer containing nitrogen-phosphorous-potassium (NPK). Rhizosphere and rhizoplane samples were collected at flowering stage (10 weeks) and analyzed by culture-independent (CI) amplicon sequence variant (ASV) analysis of rhizobacterial DNA as well as culture-dependent (CD) techniques. Rhizosphere and rhizoplane derived microbiota culture collections were tested for plant growth-promoting traits using functional bioassays. In general, fertilizer addition decreased the proportion of nutrient-solubilizing bacteria (nitrate, phosphate, potassium, iron, and zinc) isolated from rhizocompartments in wheat whereas salt tolerant bacteria were not affected. A “PGPR” database was created from isolate 16S rRNA gene sequences against which total amplified 16S rRNA soil DNA was searched, identifying 1.52% of total community ASVs as culturable PGPR isolates. Bioassays identified a higher proportion of PGPR in non-fertilized samples [rhizosphere (49%) and rhizoplane (91%)] compared to fertilized samples [rhizosphere (21%) and rhizoplane (19%)] which constituted approximately 1.95 and 1.25% in non-fertilized and fertilized total community DNA, respectively. The analyses of 16S rRNA genes and deduced functional profiles provide an in-depth understanding of the responses of bacterial communities to fertilizer; our study suggests that rhizobacteria that potentially benefit plants by mobilizing insoluble nutrients in soil are reduced by chemical fertilizer addition. This knowledge will benefit the development of more targeted biofertilization strategies.

Fortified bacterial consortium – A novel approach to control root knot nematode in cucumber (cucumis sativum)

In present era of organic farming, biocontrol agents can be further improved to obtain greater levels of disease reduction. Development of formulations with increased shelf life and broad spectrum action with consistent performance under field conditions could pave the way for commercialization of the technology at a faster rate. In present investigation plant growth promoting rhizobacterial (PGPR) consortium containing three biocontrol bacterial strains (Providencia vermicola AAU PR1 (NCBI ACCN: KJ161325), Pseudomonas putida AAU PR2 (NCBI ACCN: KJ161326) and Pseudomonas fluorescens AAU PR3 (NCBI ACCN: KJ161327) fortified with extracts of botanicals viz. Azadirachta indica (neem), Ipomoea carnea (besharam) and Brassica juncea (mustard cake) was prepared and found to effectively control M. incognita under laboratory conditions and displayed highest reduction in egg hatching after 24, 48 and 72 h of exposure. Seed coating + soil drenching of fortified PGPR consortium was found to enhance plant growth parameters and reduce root knot nematode infestation in cucumber in pot experiment as well as field. Opinion of farmers growing cucumber in protected cultivation (polyhouse / greenhouse) indicated that application of fortified PGPR consortium reduced nematode infestation and replaced chemical measures of nematode control and showed increase in yield providing dual benefit of reducing cost of cultivation with higher yield. All the experimental results signified the efficiency of fortified PGPR consortium for control of root knot nematode disease in cucumber.

Fertility Impact of Separate and Combined Treatments with Biochar, Sewage Sludge Compost and Bacterial Inocula on Acidic Sandy Soil

The short-term effects of processed waste materials: sewage sludge compost (up to 0.5%), biochar made of paper sludge and grain husk (BC) (up to 2%) combined with plant growth-promoting rhizobacterial (PGPR) inoculum, on the fertility of acidic sandy soil at 65% of field capacity were tested in a pot experiment in separate and combined treatments. The soil pH, organic matter content, total and plant-available nutrients, substrate-induced respiration, arbuscular mycorrhizal fungal (AMF) root colonisation parameters and maize (Zea mays L.) biomass were investigated in experiments lasting two months. The positive priming (21% organic matter loss) induced by BC alone was not observed after combined application. The combination of compost and PGPR with 1.5% BC resulted in 35% higher P and K availability due to greater microbial activity compared to BC alone. Only compost applied alone at 0.5% gave a 2.7 times increase in maize biomass. The highest microbial activity and lowest AMF colonisation were found in combined treatments. In the short term the combined application of BC, compost and PGPR did not result in higher fertility on the investigated soil. Further research is needed with a wider range of combined treatments on acidic sandy soil for better understanding of the process.

Characterization of plant growth-promoting alkalotolerant Alcaligenes and Bacillus strains for mitigating the alkaline stress in Zea mays.

Intensification of sodic soil due to increasing pH is an emerging environmental issue. The present study aimed to isolate and characterise alkaline stress-tolerant and plant growth-promoting bacterial strains from moderately alkaline soil (pH 8-9), strongly alkaline soil (pH 9-10), and very strongly alkaline soil (> 10). Total 68 bacteria were isolated, and screened for multiple plant growth promoting (PGP) attributes. Out of total, 42 isolates demonstrating at least three plant growth promoting PGP traits selected for further assays. Then out of 42, 15 bacterial isolates were selected based on enhanced maize plant growth under greenhouse experiment, and 16S rRNA gene sequencing revealed Bacillus spp. as a dominant genus. Furthermore, based on improved seed germination percentage and biomass of maize (Zea mays L.) under alkaline stress conditions Alcaligenes sp. NBRI NB2.5, Bacillus sp. NBRI YE1.3, and Bacillus sp. NBRI YN4.4 bacterial strains were selected, and evaluated for growth-promotion and alkaline stress amelioration under greenhouse condition. Amongst the selected 3 plant growth promoting rhizobacterial (PGPR) strains, Bacillus sp. NBRI YN4.4 significantly improved the photosynthetic pigments and soluble sugar content, and decreased proline level in inoculated maize plants as compared to uninoculated control under stress conditions. Moreover, significantly enhanced soil enzymes such as dehydrogenase, alkaline phosphatase and betaglucosidase due to inoculation of Bacillus sp. NBRI YN4.4 in maize plants grown in alkaline soil attributes to its role in improving the soil health. Therefore, alkaline stress-tolerant PGPR NBRI YN4.4 can be useful for developing strategies for the reclamation of saline/sodic soils and improving the plant growth and soil health in sustainable manner.

Antifungal activity of volatile compounds produced by endophytic Bacillus subtilis DZSY21 against Curvularia lunata

PurposeTo screen endophytic Bacillus producing volatile organic compounds (VOCs) with antifungal activity, and to explore their biocontrol properties toward the growth and pathogenicity of Curvularia lunata.MethodsTwo-sealed-base-plate assays were used to estimate the antifungal activities of Bacillus strains against C. lunata. Conjoint analysis of solid-phase microextraction gas chromatography-mass spectrometry and antagonistic experiments were used to identify the VOCs responsible for the antifungal activity. Effects of individual synthetic VOCs were analyzed along with reactive oxygen species (ROS) accumulation in C. lunata conidia. After exposure to individual VOCs, conidia were also sprayed onto maize leaves to evaluate their pathogenicity. Expression levels of virulence-related genes in C. lunata mycelium following exposure to VOCs were analyzed using quantitative real-time PCR.ResultsAmong the ten endophytic Bacillus strains and two plant growth-promoting rhizobacterial (PGPR) strains, only B. subtilis strain DZSY21 strongly inhibited the growth of C. lunata by producing VOCs. 2-Methylbutyric acid, 2-heptanone, and isopentyl acetate produced by strain DZSY21 showed inhibitory effects on the mycelia growth and conidial sporulation of C. lunata. 2-Heptanone and isopentyl acetate also repressed the germination of conidia and the expression levels of virulence-related genes in C. lunata mycelium. Moreover, isopentyl acetate strongly enhanced the accumulation of intracellular ROS in conidia. The disease indexes of maize leaves sprayed with VOC-treated C. lunata conidia were reduced from 60.52 to 26.64%.ConclusionEndophytic B. subtilis strain DZSY21 displayed the potential to control C. lunata by producing VOCs, especially 2-heptanone and isopentyl acetate.

Mixed bacterial fermentation can control the growth and development of Verticillium dahliae

Verticillium wilt is a severe disease caused by Verticillium dahliae, which afflicts many crops, particularly cotton in the Xinjiang province of China. Chemical fungicides are harmful to the environment, and biological control agents against the fungal pathogens of plants provide an alternative to chemicals. Biological control agents include antagonistic bacteria or metabolic products. We investigated the inhibitory effects of two plant-growth-promoting rhizobacterial (PGPR) strains, namely Bacillus tequilensis C-9 and Sphingobacterium A1, against V. dahliae in vitro and in the field. We used the mixed fermentation of two bacteria to inhibit V. dahliae. Antimicrobial assays were performed and showed that spore production and germination, and the virulence protein of V. dahliae were reduced after treatment with cell-free mixed fermentation broth. In field studies, there was improvement in the disease severity, along with declined incidence and index after the treatment in the bud and bell stages. To explore the molecular mechanisms of this inhibition, we studied six metabolism-related genes by real-time quantitative polymerase chain reaction (qRT-PCR). The results showed that in response to mixed fermentation broth, some genes related to growth and development were significantly upregulated, explaining the structural changes observed in V. dahliae. Some genes that regulate oxidative stress were also dramatically induced, indicating that mixed bacterial fermentation had a significant impact on V. dahliae. These results support the idea that the cell-free mixed fermentation broth of Bacillus tequilensis C-9 and Sphingobacterium A1, when applied for biocontrols, can inhibit V. dahliae in vitro and in vivo.

Three-dimensional graphene for electrochemical detection of Cadmium in Klebsiella michiganensis to study the influence of Cadmium uptake in rice plant

Cadmium (Cd), as a hazardous pollutant present in the environment as well as within biological samples, needs to be detected and remediated at the same time. Although many types of Cd detection techniques have been developed globally, there is no evidence to analyse Cd2+ ion electrochemically using graphene-based electrode for bioaccumulation of Cd in bacteria and plants. The present study describes the fabrication and characterization of a three-dimensional reduced graphene oxide-based electrode to detect bioaccumulation of Cd within the bacterial cell and rice tissues applying differential pulse voltammetry (DPV) technique. In addition, X-ray fluorescence (XRF) and X-ray diffraction (XRD) studies were performed as supporting tools for this study in the selected Cd resistant plant growth promoting rhizobacterial (PGPR) strain, Klebsiella michiganensis MCC3089. This strain was characterized based on its plant growth promoting (PGP) traits and exhibited bioaccumulation of Cd both under high and low Cd concentrations, of which the latter is more environmentally significant. The Cd-sequestration ability of this strain was found to reduce Cd uptake within rice seedlings.

Induced defense response in wheat plants against Bipolaris sorokiniana following application of Bacillus safensis and Ochrobactrum pseudogrignonense

Present study was carried out to appraise various biochemical and metabolic changes during spot blotch disease development and efficiency of two plant growth promoting rhizobacterial (PGPR) strains Bacillus safensis W10 and Ochrobactrum pseudogrignonense IP8 in promoting resistance against Bipolaris sorokiniana. In PGPR primed plants which were challenge inoculated with B. sorokiniana, disease index reduced markedly, which was about 50% in B. safensis treatment and 40% in O. pseudogrignonense. Application of PGPR decreased stress indicators like hydrogen peroxide and malonaldehyde accumulated in infected plant tissue as a response to oxidative damage promoted by lipid peroxidation under elevated free radical formation. Increased activity of defense enzymes such as, chitinase, β-1,3 glucanase, phenyl alanine ammonia lyase and peroxidase were observed in plants following application with PGPR and challenge inoculated with B. sorokiniana in comparison with untreated healthy control plants. Besides, accumulation of proline and biochemical components such as total soluble protein and total phenol in higher concentration in PGPR treated and pathogen inoculated plants was evident. Analysis of phenols by high performance liquid chromatography revealed higher accumulation of phenols such as ferulic acid, salicylic acid and caffeic acid.

Rhizosphere-associated Alcaligenes and Bacillus strains that induce resistance against blast and sheath blight diseases, enhance plant growth and improve mineral content in rice.

To examine the biocontrol activities of five rhizobacterial strains (i.e. Alcaligenes faecalis strains Bk1 and P1, Bacillus amyloliquefaciens strain Bk7 and Brevibacillus laterosporus stains B4 and S5), to control the rice blast and sheath blight diseases in greenhouse and to study their possible modes of action. Five potential plant growth-promoting rhizobacterial (PGPR) strains isolated from rice rhizospheres were tested for invitro antifungal activities against Magnaporthe oryzae, Rhizoctonia solani, Botrytis cinerea and Fusarium graminearum. In vitro trials showed that three strains, Bk1, P1 and Bk7, were able to unanimously suppress the mycelial growth of the target pathogens. In greenhouse, the application of these three PGPR strains significantly suppressed the incidences of rice blast and sheath blight diseases. At 2weeks after pathogen inoculation, the highest percentages of disease suppression were noted for Alc. faecalis strain Bk1 (72%) for rice blast, Alc. faecalis strain P1 (71%) for sheath blight, followed by B. amyloliquefaciens strain Bk7. Moreover, these strains significantly improved the plant growth, enriched the content of mineral nutrients in seedlings and increased the expression of major defence-related rice genes. All three strains were marked positive for phosphate solubilization, the production of indoleacetic acid, ammonia and siderophores and catalase activity. In addition, these strains were able to form biofilms and carried multiple lipopeptide biosynthetic genes as revealed by multiplex PCR. This study reports new potential biocontrol agents for blast and sheath blight diseases of rice. This study contributes to better understanding of the mechanisms involved in interaction between beneficial rhizobacteria, fungal pathogens and host plants.

Design, synthesis, and characterization of 2,2-bis(2,4-dinitrophenyl)-2-(phosphonatomethylamino)acetate as a herbicidal and biological active agent.

The present study was designed to synthesize the bioactive molecule 2,2-bis(2,4-dinitrophenyl)-2-(phosphonatomethylamino)acetate (1), having excellent applications in the field of plant protection as a herbicide. Structure of newly synthesized molecule 1 was confirmed by using the elemental analysis, mass spectrometric, NMR, UV-visible, and FTIR spectroscopic techniques. To obtain better structural insights of molecule 1, 3D molecular modeling was performed using the GAMESS programme. Microbial activities of 1 were checked against the pathogenic strains Aspergillus fumigatus (NCIM 902) and Salmonella typhimurium (NCIM 2501). Molecule 1 has shown excellent activities against fungal strain A. fumigates (35μg/l) and bacterial strain S. typhimurium (25μg/l). To check the medicinal significance of molecule 1, interactions with bovine serum albumin (BSA) protein were checked. The calculated value of binding constant of molecule 1-BSA complex was 1.4×106M-1, which were similar to most effective drugs like salicylic acid. More significantly, as compared to herbicide glyphosate, molecule 1 has exhibited excellent herbicidal activities, in pre- and post-experiments on three weeds; barnyard grass (Echinochloa Crus), red spranglitop (Leptochloa filiformis), and yellow nuts (Cyperus Esculenfus). Further, effects of molecule 1 on plant growth-promoting rhizobacterial (PGPR) strains were checked. More interestingly, as compared to glyphosate, molecule 1 has shown least adverse effects on soil PGPR strains including the Rhizobium leguminosarum (NCIM 2749), Pseudomonas fluorescens (NCIM 5096), and Pseudomonas putida (NCIM 2847).

In silico structural and functional analysis of Mesorhizobium ACC deaminase

Nodulation is one of the very important processes of legume plants as it is the initiating event of fixing nitrogen. Although ethylene has essential role in normal plant metabolism but it has also negative impact on plants particularly in nodule formation in legume plants. It is also produced due to a variety of biotic or abiotic stresses. 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase is a rhizobial enzyme which cleaves ACC (immediate precursor of ethylene) into α-ketobutyrate and ammonia. As a result, the level of ethylene from the plant cells is decreased and the negative impact of ethylene on nodule formation is reduced. ACC deaminase is widely studied in several plant growth promoting rhizobacterial (PGPR) strains including many legume nodulating bacteria like Mesorhizobium sp. It is an important symbiotic nitrogen fixer belonging to the class – alphaproteobacteria under the order Rhizobiales. ACC deaminase has positive role in Legume-rhizobium symbiosis. Rhizobial ACC deaminase has the potentiality to reduce the adverse effects of ethylene, thereby triggering the nodulation process. The present study describes an in silico comparative structural (secondary structure prediction, homology modeling) and functional analysis of ACC deaminase from Mesorhizobium spp. to explore physico-chemical properties using a number of bio-computational tools. M. loti was selected as a representative species of Mesorhizobium genera for 3D modelling of ACC deaminase protein. Correlation by the phylogenetic relatedness on the basis of both ACC deaminase enzymes and respective acdS genes of different strains of Mesorhizobium has also studied.