Tushar Kanti Dangar

Reduction of selenite to red elemental selenium by moderately halotolerant Bacillus megaterium strains isolated from Bhitarkanika mangrove soil and characterization of reduced product.

Two Gram (+) bacterial strains, BSB6 and BSB12, showing resistance and potential for Se(IV) reduction among 26 moderately halotolerant isolates from the Bhitarkanika mangrove soil were characterized by biochemical and 16S rDNA sequence analyses. Both of them were strictly aerobic and able to grow in a wide range of pH (4-11), temperature (4-40°C) and salt concentration (4-12%) having an optimum growth at 37°C, pH ∼7.5 and 7% salt (NaCl). The biochemical characteristics and 16S rDNA sequence analysis of BSB6 and BSB12 showed the closest phylogenetic similarity with the species Bacillus megaterium. Both the strains effectively reduced Se(IV) and complete reduction of selenite (up to 0.25 mM) was achieved within 40 h. SEM with energy dispersive X-ray and TEM analyses revealed the formation of nano size spherical selenium particles in and around the bacterial cells which were also supported by the confocal micrograph study. The UV-Vis diffuse reflectance spectra and XRD of selenium precipitates revealed that the selenium particles are in the nanometric range and crystalline in nature. These bacterial strains may be exploited further for bioremediation process of Se(IV) at relatively high salt concentrations and green synthesis of selenium nanoparticles.

Optimization and characterization of chromium(VI) reduction in saline condition by moderately halophilic Vigribacillus sp isolated from mangrove soil of Bhitarkanika, India

A Gram-positive moderately halophilic Cr(VI) tolerant bacterial strain H4, isolated from saline mangrove soil, was identified as Vigribacillus sp. by biochemical characterization and 16S rRNA analysis. In LB medium, the strain could tolerate up to 1000 mg L(-1) Cr(VI) concentration and reduced 90.2 and 99.2% of 100 mg L(-1) Cr(VI) under optimized set of condition within 70 h in absence and presence of 6 wt.% NaCl, respectively. The fitting of time course reduction data to an exponential rate equation yielded the Cr(VI) reduction rate constants in the range (0.69-5.56)×10(-2)h(-1). Analyses of total chromium and bacterial cell associated with reduced product by AAS, SEM/EDS, TEM/SAED, FT-IR and UV-vis-DRS indicated the formation of about 35% of insoluble Cr(III) either as Cr(OH)(3) precipitate in nanometric size or immobilized on the bacterial cell surface while the remaining 65% of reduced chromium was present as soluble Cr(III) in the growth medium. Powder XRD analysis revealed the amorphous nature of the precipitated Cr(OH)(3). The high Cr(VI) reducing ability of the strain under saline condition suggests the Vigribacillus sp. as a new and efficient strain capable of remediating highly saline Cr(VI) polluted industrial effluents.

Phenotypic and molecular characterization of native Azospirillum strains from rice fields to improve crop productivity

Beneficial microorganisms have been considered as an important tool for crop improvement. Native isolates of Azospirillum spp. were obtained from the rhizospheres of different rice fields. Phenotypic, biochemical and molecular characterizations of these isolates led to the identification of six efficient strain of Azospirillum. PCR amplification of the nif genes (nifH, nifD and nifK) and protein profile of Azospirillum strains revealed inter-generic and inter-specific diversity among the strains. In vitro nitrogen fixation performance and the plant growth promotion activities, viz. siderophore, HCN, salicylic acid, IAA, GA, zeatin, ABA, NH3, phosphorus metabolism, ACC deaminase and iron tolerance were found to vary among the Azospirillum strains. The effect of Azospirillum formulations on growth of rice var. Khandagiri under field condition was evaluated, which revealed that the native formulation of Azospirillum of CRRI field (As6) was most effective to elevate endogenous nutrient content, and improved growth and better yield are the result. The 16S rRNA sequence revealed novelty of native Azospirillum lipoferum (As6) (JQ796078) in the NCBI database.

A novel Azotobacter vinellandii (SRIAz3) functions in salinity stress tolerance in rice

The plant growth promoting rhizobacteria (PGPRs) as a biofertilizer provide agricultural benefits to advance various crops productivity. Recently, we discovered a novel Azotobacter vinellandii (SRIAz3) from rice rhizosphere, which is well competent to improve rice productivity. In this study, we investigated a role of A. vinellandii to confer salinity tolerance in rice (var. IR64). A. vinellandii inoculated rice plants showed higher proline and malondialdehyde content under 200 mM NaCl stress as compared with uninoculated one. The endogenous level of plant hormones viz., indole-3 acetic acid (IAA), gibberellins (GA3), zeatint (Zt) was higher in A. vinellandii inoculated plants under high salinity. The fresh biomass of root and shoot were relatively elevated in A. vinellandii inoculated rice. Further, the macronutrient profile was superior in A. vinellandii inoculated plants under salinity as compared with non-inoculated plants. The present findings further suggest that A. vinellandii, a potent biofertilzer, potentially confer salinity stress tolerance in rice via sustaining growth and improving compatible solutes and nutrients profile and thereby crop improvement.

Diversity of Bacillus thuringiensis in the rice field soils of different ecologies in India.

Diversity of the Bacillus thuringiensis (Bt) in the rice field soils of different ecologies viz. the island (Port Blair), the Himalayan (Srinagar), brackish water (Mahe) and coastal mesophilic (Mangalore) habitats was analyzed by phenotypic characterization of 5, 66, 14 and 54 Bt isolates, respectively. The Bt isolates produced either monotypic (bipyramidal or spherical) or heterotypic (polymorphic-bipyramidal or bipyramidal-rhomboidal) crystals. The organisms were generally resistant to the penicillin group of antibiotics, tolerated 5–12% NaCl and 0.5M Na-acetate. The Bt isolates contained 1–5 plasmids of 0.89–58.61 kbp sizes. The plasmid profiles had no correlation with crystal morphology or salt tolerance of different bacteria. Each soil was inhabited by different types of Bt. Two Bt strains of Mangalore and one strain each of the other places were phenotypically similar. One Bt strain each of Port Blair and Srinagar was different from all other strains.

Tuning of azine derivatives for selective recognition of Ag+ with the in vitro tracking of endophytic bacteria in rice root tissue

Several azine derivatives have been prepared and structurally characterized by spectroscopic and single-crystal X-ray diffraction analysis. Two of them, viz. naphthalene based (A10) and anthracene based (A11) show fluorescence enhancement in the presence of Ag+ in aqueous-methanol. Moreover, A11 efficiently tracks Ag+in vitro endophytic bacteria infected rice root tissue. Experimental results have been substantiated by theoretical DFT calculations.

Infectivity and ecology of Pseudomonas spp. from natural epizootics in the rice leaf folder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) in India

Abstract In 2001, populations of the leaf folder (LF) (Cnaphalocrocis medinalis Guenee) reached 19–30 larvae/hill in Rabi rice (variety Lalat) fields at Choudwar, Baranga, Alani and Tangi, Orissa, India infesting 61–98% of the plants. Three bacteria viz. Pseudomonas aeruginosa (Pa1 and Pa2) and P. fluorescens (Pf) infected 62–98% of the larvae in different fields. No correlation was found among populations of the Pseudomonas spp. on the rice phyllosphere and larvae harboring the bacteria at different fields. The median lethal concentrations (LC50s; ×103 bacteria/mL) of Pa1, Pa2 and Pf were 4–4.2, 4.8–4.9 and 5.7–5.9, respectively, for the leaf piece assay and 4.8–4.9, 5–5.1 and 6.3–6.7, respectively, for the potted plant assay against second to fifth instar larvae. The median lethal times (LT50s) were 2.1–2.4, 3.2–3.5 and 5.3–6 days for the leaf piece assay, and 4–4.7, 4.7–4.9 and 6.1–6.8 days for the potted plant assay with Pa1, Pa2 and Pf, respectively. The Pa1 and Pa2 were compatible, exhibited synergistic effect and co-inoculation reduced the LC50 and LT50 as compared to inoculation with individual organisms. The Pf had no synergism with Pa1 or Pa2, and therefore, the lethal values for Pf alone or with the other bacteria were similar. Fulfillment of Kochs postulates confirmed that Pa1, Pa2 and Pf were pathogens of C. medinalis.