Bacterial endophytes modulates the withanolide biosynthetic pathway and physiological performance in Withania somnifera under biotic stress.

Despite the vast exploration of endophytic microbes for growth enhancement in various crops, knowledge about their impact on the production of therapeutically important secondary metabolites is scarce. In the current investigation, chitinolytic bacterial endophytes were isolated from selected medicinal plants and assessed for their mycolytic as well as plant growth promoting potentials. Among them the two most efficient bacterial endophytes namely Bacillus amyloliquefaciens (MPE20) and Pseudomonas fluorescens (MPE115) individually as well as in combination were able to modulate withanolide biosynthetic pathway and tolerance against Alternaria alternata in Withania somnifera. Interestingly, the expression level of withanolide biosynthetic pathway genes (3-hydroxy-3-methylglutaryl co-enzyme A reductase, 1-deoxy-D-xylulose-5-phosphate reductase, farnesyl di-phosphate synthase, squalene synthase, cytochrome p450, sterol desaturase, sterol Δ-7 reductase and sterol glycosyl transferases) were upregulated in plants treated with the microbial consortium under A. alternata stress. In addition, application of microbes not only augmented withaferin A, withanolide A and withanolide B content (1.52-1.96, 3.32-5.96 and 12.49-21.47 fold, respectively) during A. alternata pathogenicity but also strengthened host resistance via improvement in the photochemical efficiency, normalizing the oxidized and non-oxidized fraction, accelerating photochemical and non-photochemical quantum yield, and electron transport rate. Moreover, reduction in the passively dissipated energy of PSI and PSII in microbial combination treated plants corroborate well with the above findings. Altogether, the above finding highlights novel insights into the underlying mechanisms in application of endophytes and emphasizes their capability to accelerate biosynthesis of withanolides in W. somnifera under biotic stress caused by A. alternata.

Endophyte-Mediated Modulation of Defense-Related Genes and Systemic Resistance in Withania somnifera (L.) Dunal under Alternaria alternata Stress.

Endophytes have been explored and found to perform an important role in plant health. However, their effects on the host physiological function and disease management remain elusive. The present study aimed to assess the potential effects of endophytes, singly as well as in combination, in Withania somnifera (L.) Dunal, on various physiological parameters and systemic defense mechanisms against Alternaria alternata Seeds primed with the endophytic bacteria Bacillus amyloliquefaciens and Pseudomonas fluorescens individually and in combination demonstrated an enhanced vigor index and germination rate. Interestingly, plants treated with the two-microbe combination showed the lowest plant mortality rate (28%) under A. alternata stress. Physiological profiling of treated plants showed improved photosynthesis, respiration, transpiration, and stomatal conductance under pathogenic stress. Additionally, these endophytes not only augmented defense enzymes and antioxidant activity in treated plants but also enhanced the expression of salicylic acid- and jasmonic acid-responsive genes in the stressed plants. Reductions in reactive oxygen species (ROS) and reactive nitrogen species (RNS) along with enhanced callose deposition in host plant leaves corroborated well with the above findings. Altogether, the study provides novel insights into the underlying mechanisms behind the tripartite interaction of endophyte-A. alternata-W. somnifera and underscores their ability to boost plant health under pathogen stress.IMPORTANCEW. somnifera is well known for producing several medicinally important secondary metabolites. These secondary metabolites are required by various pharmaceutical sectors to produce life-saving drugs. However, the cultivation of W. somnifera faces severe challenge from leaf spot disease caused by A. alternata To keep pace with the rising demand for this plant and considering its capacity for cultivation under field conditions, the present study was undertaken to develop approaches to enhance production of W. somnifera through intervention using endophytes. Application of bacterial endophytes not only suppresses the pathogenicity of A. alternata but also mitigates excessive ROS/RNS generation via enhanced physiological processes and antioxidant machinery. Expression profiling of plant defense-related genes further validates the efficacy of bacterial endophytes against leaf spot disease.

Protective role of biosynthesized silver nanoparticles against early blight disease in Solanum lycopersicum.

Tomato suffers a huge loss every year because of early blight disease. This study focuses on efficient inhibition of Alternaria solani, the causative agent of early blight disease in tomato in vitro and in vivo. Foliar spray of 5 µg/mL of biosynthesized silver nanoparticles in A. solani infected plants resulted in significant increase of 32.58% in fresh weight and 23.52% in total chlorophyll content of tomato as compared to A. solani infected plants. A decrease of 48.57, 30, 39.59 and 28.57% was observed in fungal spore count, lipid peroxidation, proline content and superoxide dismutase respectively in infected tomato plants after treatment with synthesized silver nanoparticles as compared to A. solani infected plants. No significant variation in terms of soil pH, cultured population, carbon source utilization pattern and soil enzymes including dehydrogenase, urease, protenase and ß-glucosidase was observed after foliar spray of nanoparticles. It was revealed that direct killing of pathogens, increased photosynthetic efficiencies, increased plant resistance and decrease in stress parameters and stress enzymes are the mechanisms employed by plants and nanoparticles simultaneously to combat the biotic stress. Biosynthesized silver nanoparticles bear the potential to revolutionize plant disease management, though the molecular aspects of increased resistance must be looked upon.

Tailoring shape and size of biogenic silver nanoparticles to enhance antimicrobial efficacy against MDR bacteria.

Spherical, rectangular, penta, and hexagonal silver nanoparticles of different dimensions were biosynthesized in an eco-friendly manner by biocontrol agent, Trichoderma viride by manipulating physical parameters, pH, temperature, and reaction time. The particles were characterized by UV-vis spectroscopy; Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Fourier Transform Infra-red Spectroscopy (FTIR). Shape and size dependent antimicrobial activity of nanoparticles against human pathogens was observed. Maximum inhibition was found with spherical nanoparticles (2-5 nm) showing 40, 51, 43, 53.9 and 55.8% against Shigella sonnei, Escherichia coli, Serratia marcescens, Staphylococcus. aureus and Pseudomonas aeruginosa respectively, where as pentagonal and hexagonal nanoparticles (50-100 nm) demonstrated 32, 41, 31, 42.84 and 42.80% of inhibition as compared to control. Nanoparticles of different geometry and dimension established enhanced antagonistic activity against pathogens with all the tested antibiotics. Excellent antimicrobial efficacy was obtained with spherical nanoparticles of 2-5 nm with ampicillin and penicillin. Shape and size played major role in enhancing antimicrobial potential of silver nanoparticles, both singly and synergistically with antibiotics which can be exploited to combat the spread of multidrug resistant pathogens.

Biocatalytic and antimicrobial activities of gold nanoparticles synthesized by Trichoderma sp.

The aim of this work was to synthesize gold nanoparticles by Trichoderma viride and Hypocrea lixii. The biosynthesis of the nanoparticles was very rapid and took 10 min at 30 °C when cell-free extract of the T. viride was used, which was similar by H. lixii but at 100 °C. Biomolecules present in cell free extracts of both fungi were capable to synthesize and stabilize the formed particles. Synthesis procedure was very quick and environment friendly which did not require subsequent processing. The biosynthesized nanoparticles served as an efficient biocatalyst which reduced 4-nitrophenol to 4-aminophenol in the presence of NaBH4 and had antimicrobial activity against pathogenic bacteria. To the best of our knowledge, this is the first report of such rapid biosynthesis of gold nanoparticles within 10 min by Trichoderma having plant growth promoting and plant pathogen control abilities, which served both, as an efficient biocatalyst, and a potent antimicrobial agent.

Constructed wetland as an ecotechnological tool for pollution treatment for conservation of Ganga river.

With aim to develop an efficient and ecofriendly approach for on-site treatment of sewage, a sub-surface flow constructed wetland (CW) has been developed by raising potential aquatic macrophytes; Typha latifolia, Phragmites australis, Colocasia esculenta, Polygonum hydropiper, Alternanthera sessilis and Pistia stratoites in gravel as medium. Sewage treatment potential of CW was evaluated by varying retention time at three different stages of plant growth and stabilization. After 6 months, monitoring of fully established CW indicated reduction of 90%, 65%, 78%, 84%, 76% and 86% of BOD, TSS, TDS, NO3-N, PO4-P and NH4-N, respectively in comparison to inlet after 36 h of retention time. Sewage treatment through CW also resulted in reduction of heavy metal contents. Thus, CW proved an effective method for treatment of wastewater and may be developed along river Ganga stretch as an alternative technology. Treated water may be drained into river to check further deterioration of Ganga water quality.

A novel method to prepare concentrated conidial biomass formulation of Trichoderma harzianum for seed application.

AIMS: To prepare concentrated formulation of Trichoderma harzianum MTCC-3841 (NBRI-1055) with high colony forming units (CFU), long shelf life and efficient in root colonization by a simple scrapping method. METHODS AND RESULTS: NBRI-1055 spores scrapped from potato dextrose agar plates were used to prepare a concentrated formulation after optimizing carrier material, moisture content and spore harvest time. The process provides an advantage of maintaining optimum moisture level by the addition of water rather than dehydration. The formulation had an initial 11-12 log(10) CFU g(-1). Its concentrated form reduces its application amount by 100 times (10 g 100 kg(-1) seed) and provides 3-4 log(10) CFU seed(-1). Shelf life of the product was experimentally determined at 30 and 40 °C and predicted at other temperatures following Arrhenius equation. The concentrated formulation as compared to similar products provides an extra advantage of smaller packaging for storage and transportation, cutting down product cost. Seed application of the formulation recorded significant increase in plant growth promotion. CONCLUSIONS: Stable and effective formulation of Trichoderma harzianum NBRI-1055 was obtained by a simple scrapping method. SIGNIFICANCE AND IMPACT OF THE STUDY: A new method for the production of concentrated, stable, effective and cost efficient formulation of T. harzianum has been validated for seed application.

Changes in the metabolome and histopathology of Amaranthus hypochondriacus L. in response to Ageratum enation virus infection.

Amaranthus hypochondriacus L. infected with Ageratum enation virus (AEV) was investigated for identifying alteration in the anatomical structures, sap translocation and metabolomic variations using light microscopy, magnetic resonance imaging, NMR spectroscopy and GC-MS, respectively. Combination of GC-MS and NMR spectroscopy identified 68 polar and non-polar metabolites that were present in different levels in healthy and virus-infected A. hypochondriacus. Contrast of T1 and T2 weighted MR images showed significant differences in the spatial distribution of water, lipids and macromolecules indicating alterations in the cortical region and disruption of vascular bundles in virus-infected stem tissues. MRI observations are supported by light microscopic examination. Microscopic examination of AEV infected stem revealed severe hyperplasia with a considerable reduction in size of stem cells. The NMR spectroscopy and GC-MS analysis indicated that viral infection significantly affected the plant primary and secondary metabolism resulting in decreased glucose and sucrose content and increase in the concentration of ß-sitosterol and stigmasterol. Higher accumulation of TCA cycle intermediates such as citric acid and malic acid in AEV infected plants indicated enhanced rate of respiratory metabolism. The viral stress significantly increases the concentration of erythritol and myo-inositol as compared to healthy ones. Lower concentration of glucose and sucrose in viral-infected stem tissues suggests decreased translocation of photosynthates in the plants. The results demonstrated potential of MRI, NMR spectroscopy and GC-MS for studying anatomical and metabolic variations in virus-infected plants.

Pseudomonas putida NBRIC19 dihydrolipoamide succinyltransferase (SucB) gene controls degradation of toxic allelochemicals produced by Parthenium hysterophorus.

AIMS: The aim of this study was to identify the gene responsible for degradation of toxic allelochemicals of Parthenium by generating Tn5-induced mutant of Pseudomonas putida NBRIC19. Furthermore, the study characterizes the mutant at physiological, biochemical and molecular level that helped in understanding the mechanisms of reducing the allelopathic inhibition of Parthenium by Ps. putida NBRIC19. METHODS AND RESULTS: Tn5 mutant S-74.3 showing inability to degrade toxic allelochemicals was selected after screening 22 000 transconjugants. Tn5 flanking SucB gene (dihydrolipoamide succinyltransferase) of Ps. putida NBRIC19 was found to be responsible for the degradation of toxic allelochemicals that also affected biofilm formation, chemotaxis and alginate production under toxic environment of allelochemicals. Phenotypic microarray data revealed that the respiratory activity of Ps. putida NBRIC19 and S-74.3 differed on 47 substrates including amino acids, carboxylic acids, peptides and some chemical inhibitors. CONCLUSIONS: Study revealed that SucB gene regulates processes either directly or indirectly in Ps. putida NBRIC19, which on inactivation made the mutant less compatible for tolerating stress. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides the first evidence for a functional role of Ps. putida SucB gene in degradation of toxic allelochemicals of Parthenium that lead to reversal of plant growth inhibition by these toxic allelochemicals. The investigation also revealed interesting features about the involvement of microbes in plant-plant allelopathic interactions.

Paenibacillus lentimorbus enhances growth of chickpea (Cicer arietinum L.) in chromium-amended soil.

Chromium (Cr), with its great economic importance in industrial use, is a major metal pollutant of the environment. It affects soil microbial activity and soil fertility, resulting in losses in yield of plants. Paenibacillus lentimorbus B-30488(r) (B-30488(r)) tolerated 200 µg ml(-1) of Cr under in vitro conditions and produced the plant growth promoting substance indole acetic acid in the presence of Cr. Our in vitro study indicates enhancement in B-30488(r) biofilm formation by sodium alginate (SA) and calcium chloride (CaCl(2)) both in absence and presence of supplemented Cr(VI) as compared to unsupplemented control. The plant growth promoting effects caused by the B-30488(r) biofilm in rhizosphere of chickpea under Cr(VI) stress suggests a phytoprotective role of B-30488(r) biofilm. Our study reflects the multifarious role of strain B-30488(r) and presents it as a potent plant growth promoting and bioremediation agent useful in Cr-contaminated rhizosphere soil, whereby the SA and CaCl(2) induced B-30488(r) biofilm on plant root acts as a shield in preventing the direct access of toxic Cr to plant tissues, thus reducing its uptake in plants.

Lagerstroemia speciosa fruit extract modulates quorum sensing-controlled virulence factor production and biofilm formation in Pseudomonas aeruginosa.

Lagerstroemia speciosa (Lythraceae) is a south-east Asian tree more commonly known as 'Jarul'. Research on health benefits suggests that the L. speciosa plant contains phytomolecules that may have antioxidant, anti-diabetic and anti-obesity properties. However, antimicrobial activities have not been reported for this plant. The ability of L. speciosa fruit extract (LSFE) to antagonize cell-to-cell communication, expression of virulence genes and factors, and biofilm formation was evaluated in Pseudomonas aeruginosa strain PAO1. Our results suggested that LSFE caused downregulation of quorum sensing (QS)-related genes (las and rhl) and their respective signalling molecules, N-acylhomoserine lactones, without affecting the growth of P. aeruginosa PAO1. Significant inhibition of virulence factors: LasA protease, LasB elastase, and pyoverdin production, was also recorded. Application of LSFE to P. aeruginosa PAO1 biofilms increased bacterial susceptibility to tobramycin. These data suggest a possible role for quorum-quenching mechanisms unrelated to static or cidal effects, and also suggest that L. speciosa could serve as a cost-effective source in the development of new QS-based antibacterial drugs.

The purB gene controls rhizosphere colonization by Pantoea agglomerans.

AIMS: To isolate the rhizosphere competence-defective transposon Tn5 mutant of Pantoea agglomerans NBRISRM (SRM) and to identify the gene causing defect in its root colonization ability. METHODS AND RESULTS: From over 5000 clones containing Tn5, one mutant P. agglomerans NBRISRMT (SRMT) showing 6 log units less colonization when compared with SRM, after 30 days in sand-nonsterilized soil assay system was selected for further work to determine the effects of the mutation on rhizosphere competence. Southern hybridization analysis of restricted genomic DNA of SRMT demonstrated that the mutant had a single Tn5 insert. SRM increased in titre to about 2 x 10(8) CFU g(-1) root, compared with the indigenous bacterial population of heterotrophs of about 5 x 10(7) CFU g(-1) root. In contrast, 30 days later, the titre value of SRMT was almost undetectable at 1 x 10(2) CFU g(-1) root, demonstrating its inability to survive and colonize the rhizosphere. Sequencing of the flanking region of the Tn5 mutant revealed that Tn5 disrupted the purB gene. CONCLUSIONS: A defect in the colonization phenotype of the SRMT was attributed to the disruption in adenylosuccinate lyase (EC 4.3.2.2) which is encoded by the pur B gene and is required for rhizosphere colonization in P. agglomerans. Significantly less exopolysaccharide and biofilm was formed by SRMT when compared to SRM, because of the disruption of the purB gene. SIGNIFICANCE AND IMPACT OF THE STUDY: This work provides the first evidence for a functional role of purB gene in rhizosphere competence and root colonization by any rhizobacteria.

Isolation and characterization of plant growth-promoting strain Pantoea NII-186. From Western Ghat forest soil, India.

AIMS: To isolate plant growth-promoting bacterium from Western Ghat forests in India. METHODS AND RESULTS: A Gram-negative, rod shaped, cream white coloured strain Pantoea NII-186 isolated from Western Ghat soil sample. The taxonomic position of the bacterium was confirmed by sequencing of 16S rRNA and phylogenetic analysis. A strain grew at a wide range of temperature ranging from 5-40 degrees C, but optimum growth was observed at 28-30 degrees C. It showed multiple plant growth-promoting attributes such as phosphate solubilization activity, indole acetic acid (IAA) production, siderophore production and HCN production. It was able to solubilize (28 microg of Ca(3)PO(4) ml(-1) day(-1)), and produce IAA (59 microg) at 28 degrees C. The solubilization of insoluble phosphate was associates with a drop in the pH of the culture medium. Pantoea sp. NII-186 tolerate to different environmental stresses like 5-40 degrees C, 0-7% salt concentration and 4-12 pH range. CONCLUSIONS: The 16S rRNA gene sequence confirmed that the isolate NII-186 was belongs to Pantoea genus and showed considerable differences in physiological properties with previously reported species of this genus. Isolate NII-186 possessed multiple attributes of plant growth-promoting activity. SIGNIFICANCE AND IMPACT OF THE STUDY: Hence in the context it is proposed that Pantoea sp. NII-186, could be deployed as an inoculant to attain the desired plant growth-promoting activity in agricultural environment.

Biocontrol efficacy of Bacillus subtilis strains isolated from cow dung against postharvest yam (Dioscorea rotundata L.) pathogens.

The biocontrol potential of Bacillus subtilis isolated from cow dung microflora was investigated in vitro and in vivo against two postharvest yam pathogenic fungi, Fusarium oxysporum and Botryodiplodia theobromae. B. subtilis strains inhibited the growth of F. oxysporum and B. theobromae in vitro in liquid medium in the range of 49.3-56.6% and in solid medium in the range of 31.0-36.0%, in comparison to the corresponding growth of fungi without bacterial inoculation. The interaction between B. subtilis CM1 and F. oxysporum was also studied by scanning electron microscopy. Chitinase production was demonstrated in vitro when B. subtilis was grown in the presence of colloidal chitin as the sole carbon source in a liquid medium. In vivo study showed that B. subtilis strains inhibited the growth of fungi (F. oxysporum and B. thobromae) up to 83% in wound cavities of yam tubers.

Effect of high temperature on Pseudomonas putida NBRI0987 biofilm formation and expression of stress sigma factor RpoS.

Pseudomonas is an efficient plant growth-promoting rhizobacteria; however, among the limiting factors for its commercialization, tolerance for high temperature is the most critical one. After screening 2,500 Pseudomnas sp. strains, a high temperature tolerant-strain Pseudomonas putida NBRI0987 was isolated from the drought-exposed rhizosphere of chickpea (Cicer arietinum L. cv. Radhey), which was grown under rain-fed conditions. P. putida NBRI0987 tolerated a temperature of 40 degrees C for < or = 5 days. To the best of our knowledge, this is the first report of a Pseudomnas sp. demonstrating survival estimated by counting viable cells under such a high temperature. P. putida NBRI0987 colony-forming unit (CFU)/ml on day 10 in both the absence and presence of MgSO4 x 7H2O (MgSO4) in combination with glycerol at 40 degrees C were 0.0 and 1.7 x 10(11), respectively. MgSO4 plus glycerol also enhanced the ability of P. putida NBRI0987 to tolerate high temperatures by inducing its ability to form biofilm. However, production of alginate was not critical for biofilm formation. The present study demonstrates overexpression of stress sigma factor sigma(S) (RpoS) when P. putida NBRI0987 is grown under high-temperature stress at 40 degrees C compared with 30 degrees C. We present evidence, albeit indirect, that the adaptation of P. putida NBRI0987 to high temperatures is a complex multilevel regulatory process in which many different genes can be involved.

Biologic control ability of plant growth-promoting Paenibacillus lentimorbus NRRL B-30488 isolated from milk.

A plant growth-promoting Paenibacillus lentimorbus NRRL B-30488 (B-30488) was isolated from cows' milk. Bacterial colonization and growth responses of different plant species after inoculation with B-30488 were evaluated in a controlled environment and in microplot assays. Survival and colonization of B-30488 in the phytosphere of plants and soil was monitored using a chromosomally located rifampicin-marked mutant B-30488 (B-30488R). The strain showed variable ability to invade plants. The interaction between B-30488R and Fusarium oxysporum f. sp. ciceri was studied by scanning electron microscopy. Chitinase and beta-1,3-glucanase enzymes were produced when B-30488R was grown in the presence of colloidal chitin as sole carbon source. Deliberate dilution of B-30488R with field soil offers a reliable process for decreasing the cost of bacterial inoculants in developing countries. Seed treatment of chickpea demonstrated significantly (P = 0.05) greater seedling mortality in nonbacterized compared with bacterized seedlings. Bacterization significantly (P = 0.05) improved seed germination, plant height, number of pods/plant(-1), and seed dry weight.

An efficient method for qualitative screening of phosphate-solubilizing bacteria.

An efficient protocol was developed for qualitative screening of phosphate-solubilizing bacteria, based upon visual observation. Our results indicate that, by using our formulation containing bromophenol blue, it is possible to quickly screen on a qualitative basis the phosphate-solubilizing bacteria. Qualitative analysis of the phosphate solubilized by various groups correlated well with grouping based upon quantitative analysis of bacteria isolated from soil, effect of carbon, nitrogen, salts, and phosphate solubilization-defective transposon mutants. However, unlike quantitative analysis methods that involve time-consuming biochemical procedures, the time for screening phosphate-solubilizing bacteria is significantly reduced by using our simple protocol. Therefore, it is envisaged that usage of this formulation based upon qualitative analysis will be salutary for the quick screening of phosphate-solubilizing bacteria. Our results indicate that the formulation can also be used as a quality control test for expeditiously screening the commercial bioinoculant preparations, based on phosphate solubilizers.

Crossing the limits of Rhizobium existence in extreme conditions.

An ecological survey was conducted to characterize 5000 Rhizobium sp. sesbania strains of diverse geographical origin, isolated from the root nodules of Sesbania aculeata growing in neutral (pH 7) and alkaline (pH 8.5 and above) soils. The rhizobia from the alkaline soil showed significantly higher salt tolerance than those isolated from neutral soil. Upper limits of stress survival of rhizobial isolates, Rhizobium sp. NBRI0102 sesbania selected from neutral soil, and Rhizobium sp. NBRI2505 sesbania selected from alkaline soil, were studied under free living conditions. Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania tolerated yeast extract mannitol broth (YEB) containing 10% and 28% salt (NaCl, wt/vol) for up to 18 h of incubation at 30 degrees C. Growth of Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania at pH 7, 11, and 12 was identical, except for a lag period of about 10 h in the growth of Rhizobium sp. NBRI0102 sesbania at pH 11 and 12, as compared with pH 7. Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania survived at 50 degrees C and 65 degrees C, in YEB at pH 7 for up to 4 and 2 h, respectively. To our knowledge, this is the first report of rhizobia demonstrating survival of Rhizobium sp. NBRI2505 sesbania, estimated by counting viable cells, to such extreme conditions of salt and temperature, individually. In contrast to Rhizobium sp. NBRI0102 sesbania, high temperature was tolerated efficiently by Rhizobium sp. NBRI2505 sesbania, in the presence of salt at higher pH. Our results suggest that the possession of the trait of high salt tolerance might be of some evolutionary significance for the survival of rhizobia in alkaline soils, at high pH and temperature.

Effects of salt and pH stress on temperature-tolerant Rhizobium sp. NBRI330 nodulating Prosopis juliflora.

A study was conducted to examine the growth response of a rhizobial strain Rhizobium sp. NBRI330 isolated from root nodules of Prosopis juliflora growing in alkaline soil. The strain had the ability to nodulate P. juliflora. Nursery grown plants inoculated with Rhizobium sp. NBRI330 had 60.6% higher plant dry weight, as compared with uninoculated plants. The individual stress survival limit of a rhizobial strain Rhizobium sp. NBRI330 isolated from alkaline soil in a medium containing 32% (wt/vol) salt was 8 h, and at 55 degrees C up to 3 h. The length of Rhizobium sp. NBRI330 in salt-stressed cells increased significantly to 3.04 microm from 1.75 microm of non-stressed control cells. On the contrary, the length of pH-stressed cells declined to 1.40 microm. Compared with non-stressed control rod-shaped cells, the shape of temperature-stressed cells changed to spherical, of 0.42 microm diameter. High temperature (45 degrees C) was tolerated efficiently by Rhizobium sp. NBRI330 in the presence of salt at pH 12, as compared with pH 7.

Stress induced phosphate solubilization in bacteria isolated from alkaline soils.

Phosphate solubilizing bacteria NBRI0603, NBRI2601, NBRI3246 and NBRI4003 were isolated from the rhizosphere of chickpea and alkaline soils. All four strains demonstrated diverse levels of phosphate solubilization activity under in vitro conditions in the presence of various carbon and nitrogen sources. Acid production may have contributed to phosphate solubilization, but was not the only reason for phosphate release into the medium. Among the four strains, NBRI2601 was the most efficient strain in terms of its capability to solubilize phosphorus in the presence of 10% salt, pH 12, or 45 degrees C. The strains showed varied levels of phosphate solubilization when the effects of different sources of nitrogen were examined during growth. The presence of low levels of Ca(2+) and EDTA in the medium enhanced phosphate solubilization.