Browsing by Author "Ashwani Kumar Rai"

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Airborne algae: Their present status and relevance
(2007) Naveen Kumar Sharma; Ashwani Kumar Rai; Surendra Singh; Richard Malcolm Brown Jr.
Ongoing climatic changes coupled with various natural processes and the outcomes of human activities are not only loading the atmosphere with diverse kinds of biological particles but also changing their prevalence and spatial distribution. Despite having considerable ecological and economic significance, including their possible impact on human health, airborne algae are the least-studied organisms in both aerobiological and phycological studies. The present review has been written to bring together all available information, including a brief survey of the literature, the ecology of airborne algae, mechanisms involved in their aerosolization, the role of environmental factors in shaping the structure and composition of aero-algal flora, and other significant information associated with airborne algae. This review provides information on methodological approaches and related problems, along with suggestions for areas of future research on airborne algae. © 2007 Phycological Society of America.
ATP-dependent uptake of nitrate in Nostoc muscorum and inhibition by ammonium ions
(1981) Ashwani Kumar Rai; Ajai K. Kashyap; Sewa L. Gupta
A high rate of nitrate uptake was observed in Nostoc muscorum when cells were grown on elemental nitrogen as compared to that when they were grown on nitrate or ammonium. The uptake of nitrate was light dependent. However, supplementation with ATP (50 μM) stimulated nitrate uptake both in light and darkness. ADP, under similar conditions had no effect. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2-n-heptyl-4-hydroxyquinoline, (HOQNO) and KCN inhibitied nitrate uptake in light which could be partially reversed by adition of ATP. Inhibitiion by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), an uncoupler of photophosphorylation, was complete and could not be restored by the addition of ATP. N,N′-dicyclohexylcarbodiimide (DCCD), a specific inhibitor of ATPase, blocked nitrate uptake in the presence or absence of externally added ATP. Although no nitrate uptake was observed under anaerobic conditions in dark, addition of ATP resulted in uptake of nitrate, which was similar in magnitude to that observed under aerobic condition in the light, and was inhibited by DCCD. Ammonium ions inhibited the uptake of nitrate in the absence of ATP but in its presence there was simultaneous uptake of nitrate and ammonium ions. However, uptake of ammonium ions alone was not affected by presence or absence of ATP in the external medium. It was concluded that nitrate ion uptake was energy dependent and may be linked with a proton gradient which can be formed either by photophosphorylation or ATP hydrolysis. © 1981.
Biochemical characteristics of photosynthetic response to various external salanities in halotolerant and fresh water cyanobacteria
(1990) Ashwani Kumar Rai
The effect of various salinities on photosynthetic carbon fixation, activities of carboxylating enzymes, and contents of chlorophyll and protein, was examined in a halotolerant (Aphanothece halophytica) and fresh water (Aphanothece stagnina) cyanobacterium. These parameters were quantified immediately and after 48 h incubation in altered salinities. Photosynthetic carbon fixation was lower at altered salinities than in controls in both species. A. halophytica with 48 h incubation showed increased carbon fixation with increasing NaCl concentration, whereas A. stagnina did not. Chlorophyll content was drastically reduced for all salinities in A. stagnina but was unchanged in A. halophytica. d-ribulose-1,5-bisphosphate carboxylase (RuBisCO) activity from A. halophytica increased at higher external salinities but decreased in cells of A. stagnina. In vitro, the sensitivity of RuBisCO to NaCl from both the species was similar. It was noted that in A. stagnina NaCl affected chlorophyll content, carbon fixation, and RuBisCO activity in decreasing order. © 1990.
Biosorption of Cr(VI) and Ni(II) onto Hydrilla verticillata dried biomass
(Elsevier B.V., 2014) Ashutosh Mishra; Brahma Dutt Tripathi; Ashwani Kumar Rai
In the present study Hydrilla verticillata dried biomass was modified by Fenton reagent and its technical feasibility for removal of Cr6+ and Ni2+ ions from wastewater were investigated. Fenton modification process was optimized by varying pH, biosorbent dose, contact time, and Fe2+/H2O2 ratio. For Fenton modification process the optimum values of pH, biosorbent dose, contact time, and Fe2+/H2O2 ratio were 4, 70mgL-1, 70min and 0.04 w/w, respectively. The modified biosorbent was characterized by using SEM-EDX, FT-IR and Malvern particle size analyzer. SEM-EDX analysis revealed the enhancement in weight percent of Cr6+ (47.38%) and Ni2+ (41.26%) ions on the surface of Fenton modified dried biomass of Hydrilla verticillata (FMB) after biosorption. Maximum biosorption of Cr6+ and Ni2+ ions were observed to be 29.43 and 48.72mgg-1 for raw biomass and 107.64 and 106.12mgg-1 for Fenton modified biomass respectively. Experimental data were modeled using single and multi-component isotherm models. For single-metal component, the Freundlich isotherm model fits the data better than the Langmuir isotherm model. In case of binary-metal solution the experimental data show good agreement with multi-component Freundlich isotherm model. The enhancement in the overall biosorption capacity after the Fenton modification was observed which follows the sequence: Cr6+>Ni2+. The biosorption process followed the pseudo-second order kinetics. The equilibrium data suggest the involvement of chemisorption mechanism. Positive values of enthalpy and negative values of Gibbs free energy obtained during thermodynamic study revealed that the biosorption process was endothermic and spontaneous in nature. © 2014 Elsevier B.V.
Kinetics and regulation of urea uptake in anabaena doliolum and anacystis nidulans
(1987) Ashwani Kumar Rai; Surendra Singh
The apparent Kmand Vmax values for urea uptake in Anabaena doliolum Bharadwaja were 250 μM and 568 nmol of urea (mg protein)-1 hr-1. In comparison, Anacystis nidulans IU 625 showed lower affinity, Kmbeing 400μM and Vmax 500 nmol of urea (mg protein)-1 hr-1. Urea uptake was optimal at pH 7.5, 15 Wm-2 illumination and 30°C. Maximum uptake was evident during the exponential growth phase. Cells pregrown on N2, urea or nitrate transported urea equally well, but there was essentially no uptake of urea in cells preincubated with ammonia for more than 24 hr. Nevertheless, ammonia did not inhibit urea uptake by urea grown cells. But the uptake of ammonia was reduced in the presence of urea. N-deficiency invariably stimulated uptake of urea. Experiments under different metabolic conditions revealed that uptake is an active process driven mainly by cyclic photophosphorylation. © 1987, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.
Packed-bed column biosorption of chromium(VI) and nickel(II) onto Fenton modified Hydrilla verticillata dried biomass
(Academic Press, 2016) Ashutosh Mishra; Brahma Dutt Tripathi; Ashwani Kumar Rai
The present study represents the first attempt to investigate the biosorption potential of Fenton modified Hydrilla verticillata dried biomass (FMB) in removing chromium(VI) and nickel(II) ions from wastewater using up-flow packed-bed column reactor. Effects of different packed-bed column parameters such as bed height, flow rate, influent metal ion concentration and particle size were examined. The outcome of the column experiments illustrated that highest bed height (25 cm); lowest flow rate (10 mL min−1), lowest influent metal concentration (5 mg L−1) and smallest particle size range (0.25–0.50 mm) are favourable for biosorption. The maximum biosorption capacity of FMB for chromium(VI) and nickel(II) removal were estimated to be 89.32 and 87.18 mg g−1 respectively. The breakthrough curves were analyzed using Bed Depth Service Time (BDST) and Thomas models. The experimental results obtained agree to both the models. Column regeneration experiments were also carried out using 0.1 M HNO3. Results revealed good reusability of FMB during ten cycles of sorption and desorption. Performance of FMB-packed column in treating secondary effluent was also tested under identical experimental conditions. Results demonstrated significant reduction in chromium(VI) and nickel(II) ions concentration after the biosorption process. © 2016 Elsevier Inc.
Physiological, biochemical and molecular responses of the halophilic cyanobacterium Aphanothece halophytica to Pi-deficiency
(2013) Keshwanand Tripathi; Naveen Kumar Sharma; Hakuto Kageyama; Teruhiro Takabe; Ashwani Kumar Rai
We studied the responses of a halophilic cyanobacterium Aphanothece halophytica at surplus (normal composition of growth medium containing 125 μM PO43-), sufficient (the minimum concentration supporting optimal growth, 22 μM PO43-) and deficient (no external supply of Pi) concentrations of inorganic phosphate (Pi). The cyanobacterium was able to grow well in Pi-deficient conditions until the end of incubation (14 days), though at a marginally reduced rate. The cellular P-quota in Pi-surplus cells at the end of incubation was 2.7 times that of their initial P-quota (0.75 μmol mg protein-1), and remained fairly high (0.442 μmol mg protein-1) even in Pi-deficient medium. However, cultures growing in Pi-sufficient medium (22 μM PO43-), upon transfer to Pi-deficient medium, exhibited a rapid decline in cellular P level. Furthermore, cells growing in Pi-surplus medium showed a rapid efflux of P into the external medium. Aphanothece halophytica exhibited a biphasic phosphate transport system involving both high- (Ks 2.06 μM) and low-affinity (Ks 17.85 μM) transporters. Cyanobacterial cells maintained a basal level (constitutively expressed and not affected by Pi availability) of alkaline phosphatase (APase) activity, which increased 5-7-fold under Pi-deficiency. Supplementation of phosphate to the medium caused gradual decline in the enzyme activity to the basal level. Pi-deficient cells showed an enhanced level of transcripts for PPi-dependent glycolytic enzymes. Though moderate, Pi-deficiency affected the respiration, photosynthetic rate and electron transport chain activity negatively. PS II activity was most sensitive to Pi-deficiency, followed by PSI and whole chain. Pi-replete A. halophytica cells showed a single high-affinity nitrate transport system. However, deficiency of Pi reduced the nitrate and nitrite reductase activities. © 2013 © British Phycological Society.
Purification and properties of urease from a cyanobacterium Anabaena doliolum
(1989) Ashwani Kumar Rai
Urease was purified 39 fold from extracts of Anabaena doliolum. The enzyme had a MW of 228 000 as determined by gel filtration and consisted of six subunits of identical size with a MW of 36 000. The enzyme activity was optimum at pH 7.0 and at 40°C with a Km of 115 μM. Among the metal ions tested, Hg2+, Ag2+ and Cu2+ inhibited enzyme activity in decreasing order. p-hydroxymercuribenzoate (10 μM) and acetohydroxyamic acid (100 μM) brought about a total inhibition of urease activity. © 1989.
Quantitative dissection of antioxidative bioactive components in cultivated and wild sesame germplasm reveals potentially exploitable wide genetic variability
(Korean Society of Crop Science, 2014) Niti Pathak; Ashwani Kumar Rai; Supradip Saha; Suresh Walia; Soumitra Kumar Sen; Kangila Venkataraman Bhat
Sesame (Sesamum indicum L.) is one of the oldest oilseed crops grown in India and worldwide. This oilseed crop has high nutritional value due to the presence of antioxidants such as lignans and tocopherols. Screening of oilseed germplasm for important nutritional attributes is of prime importance in quality breeding programs. In the present study, the content of lignans (sesamin and sesamolin) and tocopherol homologues (α-, γ-, and δ-tocopherol) was determined using reverse phase HPLC (RP-HPLC) in 143 sesame lines collected from diverse agro-ecological zones of India. Exploitable levels of sesamin, sesamolin, γ-, and δ-tocopherol was observed in the studied sesame lines. Sesamum indicum cultivar CO 1, introgressed line MKN 9, and Sesamum malabaricum showed high values for sesamin. Exotic and indigenous accessions of S. indicum (EC 542283 and IC 132176, IC 204681, IC 204773) showed high sesamolin contents. Cultivars, AKT 64, AKT 101, Phule til 1, and Tapi A showed high values for γ- and δ-tocopherol. The average content of sesamin and sesamolin was 0.86 and 0.50 mg g-1 seed, respectively. The average tocopherol content (292 μg g-1 seed) found in this study indicates the presence of a high amount of tocopherol in Indian sesame germplasm. Superior genotypes of sesame reported in this study could be utilized in sesame breeding programs for enhancing oil yield and nutritional attributes. © 2014 Korean Society of Crop Science and Springer Science+Business Media Dordrecht.
Regulation of nitrate uptake in Nostoc muscorum by glutamine synthetase
(1982) Ashwani Kumar Rai; Surendra Singh
[No abstract available]
Salinity tolerance and growth analysis of the cyanobacterium Anabaena doliolum
(Springer-Verlag, 1993) Ashwani Kumar Rai; Gerard Abraham
[No abstract available]
Separation of bioactive metabolites from aphanothece halophytica through hplc and characterization of the analytes through ESI-MS and NMR
(Bentham Science Publishers B.V., 2013) Rashi Vishwakarma; Ashwani Kumar Rai
Separation and retention of both polar and nonpolar compounds by the same stationary phase can be a useful approach for analyses of complex samples. Biological samples encompass a broad range of polarities and varied chemical properties. A gradient elution run with acetonitrile-water as the mobile phase was used for the separation of polar and non polar compounds from Aphanothece halophytica using ODS C18 column with photo diode array detection. The various fractions collected were identified through Electrospray ionisation-mass spectrometry (ESI-MS) and Nuclear Magnetic Resonance (NMR) analyses. The High Performance Liquid Chromatography (HPLC) method provided good baseline separation of all the compounds in 15 min without the need for sample derivatization. Retrospective review of ESI-MS and NMR data identified the major compounds as nostocyclamide, trimethylglycine, phosphatidyl glycerol. © 2013 Bentham Science Publishers.
Urease of blue-green algae (Cyanobacteria)Anabaena doliolum and Anacystis nidulans
(Springer-Verlag, 1987) Ashwani Kumar Rai; Surendra Singh
Urease from Anabaena doliolum and Anacystic nidulans showed maximum activity at pH 7.0-7.4 at 40°C when measured in cell-free, phosphate-buffered extracts. It is a soluble enzyme located in cytoplasm. The apparent Km for A. doliolum urease was 120 μM. Anacystis nidulans urease exhibited biphasic kinetics (Km=250 μM and 1.66 m M). Enzyme, fully expressed in cells grown with urea, nitrate, or N2, was repressed in ammonia-grown cells, but ammonia did not inhibit the activity in vitro. Incubation of algal cells in N2 medium with chloramphenicol for 12 h caused degradation of urease. Cu2+ at 1 μM inhibited the enzyme activity by 50%, whereas Co2+ and Ni2+ up to 20 μM had no effect. p-Hydroxymercuribenzoate appeared to be a more powerful inhibitor of urease than acetohydroxamic acid. © 1987 Springer-Verlag New York Inc.