Meenu Saraf

Salinity-resistant plant growth promoting rhizobacteria ameliorates sodium chloride stress on tomato plants.

Abstract Salinity is one of the major anthropogenic as well as environmental stresses that reduce plant growth. Results show that even after being adapted up to 6% sodium chloride (NaCl) concentration, all selected isolates were able to solubilize phosphate, and produce phytohormones, siderophores and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzyme. NT1 was found to exhibit the highest phosphate solubilization zones (25 mm), siderophore production (1000 µg ml−1) as well as ACC deaminase production (50 µMmg−1h−1) potential under laboratory conditions. On the other hand, pot studies conducted on tomato plants under 2% NaCl stress proved that C4 and T15 were the best growth promoters. C4 showed 50% enhancement in root and shoot length as compared to NaCl added untreated plants as well as in absence of NaCl. C4 also enhanced salinity tolerance in plants with the lowest uptake of NaCl thereby reducing the salt stress on plants. C5 enhanced biomass production in tomato plants with increased uptake of the salts by plants, thereby reducing the salt concentration in the soil. The study thus shows that the selected isolates can be used for the plant growth promotion of plants under salinity stress.

Role of allelochemicals in plant growth promoting rhizobacteria for biocontrol of phytopathogens

Soil borne fungal diseases pose serious constraints on agro-productivity. Biological control is non-hazardous strategy to control plant pathogens and improve crop productivity. PGPR (plant growth promoting rhizobacteria) have long been used as plant disease control agents. PGPR produced a wide range of secondary compounds that may act as signals--that is, allelochemicals that include metabolites, siderophores, antibiotics, volatile metabolites, enzymes and others. Their mode of action and molecular mechanisms provide a great awareness for their application for crop disease management. The present review highlights the role of PGPR strains, specifically referring to allelochemicals produced and molecular mechanisms. Further research to fine tune combinations of allelochemicals, plant-microbe-pathogen interaction will ultimately lead to better disease control.

Enhancement of plant growth and decontamination of nickel-spiked soil using PGPR.

Phytoremediation i.e. the use of plants to adsorb, accumulate or detoxify contaminants is an emerging area of interest. A viable technology needs optimum biomass production in metal contaminated soil. Five strains of microbes were selected after testing their potential as plant growth promoters, on the basis of their phosphate solubilization ability, IAA, siderophore and HCN production and biocontrol potentials. They were examined for growth in synthetic medium supplemented with nickel and their MIC (2 mM) was determined. These isolates were also able to grow and produce siderophores in presence of heavy metals like Ni, Zn and Cd. A positive response of bacterial inoculants was observed in chickpea plants towards toxic effect of nickel present in soil at different concentration (0, 1 and 2 mM). Bacterial inoculants enhanced fresh and dry weight of plants even at 2 mM nickel concentration. Pot experiments indicated that presence of nickel at upto 1 mM enhanced plant growth compared to uninoculated nickel free plants. The accumulation of nickel/plant was just 50% in Pseudomonas inoculated plants as compared to uninoculated plants with 2 mM nickel concentration along with increased biomass. The results suggest the use of these PGPR to enhance plant growth in nickel‐spiked land and remediate nickel from contaminated sites. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bacteria in Agrobiology: Crop Productivity

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Isolation of Rhizobacteria from Jatropha curcas and characterization of produced ACC deaminase.

Decreased levels of ACC (1‐aminocyclopropane‐1‐carboxylic acid) result in lower levels of endogenous ethylene, which eliminate the potentially inhibitory effects of stress‐induced higher ethylene concentrations. It is worth noting the substantial ability of the bacterial species to colonize different environments, including taxonomically distinct plants cultivated in distantly separated geographical regions. For example, Enterobacter cloacae, designated as MSA1 and Enterobacter cancerogenus, designated as MSA2 were recovered from the rhizosphere of Jatropha in the present work. This study first time confirms the ACC deaminase activity in the Enterobacter cancerogenus on the preliminary basis. Several bacterial plant growth‐promoting mechanisms were analyzed and detected like phosphate solubilization, siderophore production, IAA production, GA3 (gibberellic acid) production and ACC deaminase activity in the isolated cultures. Isolates were grown until exponential growth phase to evaluate their ACC deaminase activity and the effect of pH, temperature, salt, metals and substrate concentration after the partial purification of enzyme by ion exchange chromatography. The FOURIER TRANSFORM INFRARED (FT‐IR) spectra were recorded for the confirmation of α‐ketobutyrate production. By using lineweaver Burk plot Km and Vmax value for ACC deaminase of both the organism was calculated in the different fractions. In this work, we discuss the possible implications of these bacterial mechanisms on the plant growth promotion or homeostasis regulation in natural conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Combinatorial assessment on dominance and informative diversity of PGPR from rhizosphere of Jatropha curcas L.

The extensive and enduring challenges in soil microbiology depend on the development of efficient methods to be acquainted with the types of microbes present in soil, and to determine the functional performance of the overall microbial groups in situ. This study aims to investigate the combined uses of species richness and diversity as well as to estimate the combinatorial effect of species richness and diversity in order to understand their role and distribution in their habitat. To achieve this objective a study was designed targeting the rhizosphere of Jatropha curcas L. which were planted in various soil conditions on five distinctive sites of Gujarat state (India). These sites were constantly monitored and studied for the species richness and evenness (“heterogeneity”). The isolates were checked for their PGPR potentials like Phosphate solubilisation, Siderophore production, Indole acetic acid production, ACC deaminase production, HCN production, EPS production and Ammonia production. The results obtained were used to calculate richness, evenness and diversity indices. Results reveal the total heterogeneity in the site of fertile Jatropha rhizosphere (GS4) as well as sodic soil site (GS5) than other three sites. Absence of equitability under the selected and defined condition was also observed in GS4 and GS5 sites. The combinatorial estimates provide the information on their distribution and roles in the habitat. In particular, such an empirical relationship from a single rhizosphere of a distinctive species Jatropha is useful to test diversity predictions in natural sites, and further it can be applied to either by performing trials over larger spatial and temporal scales or by conducting correlational studies of biodiversity gradients. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Role of ACC Deaminase Producing PGPR in Sustainable Agriculture

The plant rhizosphere is a multidimensional and dynamic ecological environment of complicated microbe–plant interactions for harnessing essential macro and micronutrients from a limited nutrient pool. Certain plant growth promoting rhizobacteria (PGPR) contain a vital enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (EC 4.1.99.4), which regulates ethylene production by metabolizing ACC (an intermediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia. The microbial enzyme 1-aminocyclopropane-1-carboxylate deaminase cleaves ACC irreversibly, this being the immediate precursor of ethylene in plants. ACC deaminase-expressing PGPR protect plants against the growth inhibition that might otherwise result following flooding, extremes of temperature, the presence of organic and inorganic toxicants, phytopathogens, drought or high salt concentrations. Organisms containing ACC deaminase genes have been reported to be useful in promotion of early root development from either seeds or cuttings, increasing the life of horticultural flowers, protecting plants against a wide range of environmental stresses, facilitating the production of volatile organic compounds responsible for aroma formation and phytoremediation of contaminated soils.

Enterobacter : Role in Plant Growth Promotion

It is believed that inoculation with rhizobacteria containing plant growth promoting (PGP) characteristics consequently promote root and shoot growth. Further evaluation of these bacteria exhibiting multiple PGP traits on soil–plant system is needed to uncover their efficacy as effective PGP rhizobacteria (PGPR) or PGP bacteria (PGPB) depending upon their nature. The genera within the family Enterobacteriaceae that feature members described as PGPB are Citrobacter, Enterobacter, Erwinia, Klebsiella, Kluyvera, Pantoea and Serratia, although some of these genera also contain species reported to be plant pathogens. Genus Enterobacter is a Gram-negative, straight rod which is motile with peritrichous flagella and is facultatively anaerobic. Enterobacter spp. are known to have a wide range of PGP characteristics involving in nitrogen fixation, soil phosphorus solubilisation, production of antibiotics, having ability to secrete siderophore produce, chitinase, ACC deaminase, hydrolytic enzymes besides exopolysaccharides and in the enhancement of soil porosity. Numerous Enterobacter strains express these activities which promote plant growth and suppress soilborne plant pathogens. These PGP abilities of Enterobacter can make them a potential candidate suitable for plant growth and development. Due to their multifarious role in crop growth, a number of these strains have been developed commercially as plant growth promoters and biocontrol agents.

Evaluation and biochemical characterization of a distinctive pyoverdin from a pseudomonas isolated from chickpea rhizosphere

Microbial siderophores confiscate the available ferric ions around the roots and trigger a reaction resulting in plant growth promotion. In our study, a high level of siderophore production was observed from a newly isolated Pseudomonas sp. from the rhizosphere of Chickpea plants. Under an iron depleted condition in Standard Succinic acid medium a 1000 μgmL-1 of siderophore production was achieved. Increasing the concentration of iron showed an inverse relationship between growth and siderophore production. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the purified crystals, its UV spectral analysis and High Pressure Liquid Chromatography (HPLC) revealed the identity of the siderophore as similar to that of pyoverdin with distinctive characters. Electron spray ionization mass spectroscopy (ESIMS) shows presence of abundance of A1 ions (419 m/z) and branching of amino acids from B1-B5. This pyoverdin contains a cyclic tetra peptide but Serine and Arginine are missing. Based on our analysis and deviations from the reported structure of pyoverdin it is suggested that this pseudomonas produces distinctly characterized pyoverdin siderophore.

Isolation and identification of allelochemicals produced by B. sonorensis for suppression of charcoal rot of Arachis hypogaea L.

Bacillus sonorensis MBCU2 isolated from vermicompost‐amended soil from Gujarat, India showed most antagonistic activity against Macrophomina phaseolina by dual culture screening. The culture supernatant of MBCU2 completely suppressed the mycelia growth of pathogen, indicating that suppression was due to the presence of allelochemicals in the culture filtrate. Results of scanning electron microscopy revealed that MBCU2 caused morphological alteration in mycelia of M. phaseolina as evident by hyphal lysis and perforation. Lipopeptides (iturin A and surfactin) produced by MBCU2 were detected and identified by MALDI‐TOF‐MS as well as liquid chromatography coupled with ESI‐MS/MS. Pot trial studies conducted by seed bacterization with MBCU2 resulted in statistically significant increase in Arachis hypogaea L. vegetative growth parameters such as root length (91%), shoot length (252%), fresh weight (71%), dry weight (57%), number of pod (128%), and number of seed (290%) in M. phaseolina infested soil over control as well as decreased M. phaseolina disease severity. We suggest that allelochemicals production can be linked to the mechanism of protection of A. hypogaea L. from M. phaseolina by B. sonorensis MBCU2.