Browsing by Author "A.K. Kashyap"

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A comparative account of the microbial biomass-N and N-mineralization of soils under natural forest, grassland and crop field from dry tropical region, India
(Institute of Agricultural and Food Information, 2009) Jay S. Singh; D.P. Singh; A.K. Kashyap
This study investigated microbial biomass-N (MB-N) and N-mineralization in soils of four different vegetation systems including forest (sal), mixed forest, savanna and cropland ecosystems in the Vindhyan region, India. A change was noted in the above region due to physiographic differences and anthropogenic disturbances. Annually the soil moisture (SM) content across the different study sites ranged from 7.5 to 24.3% being maximum in forest sites compared to savanna and cropland sites. The NH4+-N, NO 3--N and MB-N concentrations varied from 4.3 to 10.2 μg/g; 1.1 to 5.8 μg/g and 21.3 to 90.2 μg/g dry soil, respectively, with minimum values in the wet and maximum values in the dry season. The trend of seasonal variation in net N-mineralization was similar to that of moisture content but counter to the concentrations of inorganic-N and MB-N. The net N-mineralization rates at different investigated sites ranged from 4.5 to 37.6 μg/g month. Cultivation reduced the N-mineralization and MB-N by 58.5% and 63.5%, respectively. Experiments showed that the percentage contribution of MB-N to total-N was 8.01 to 19.15%. MB-N was positively correlated with the inorganic-N (n=180, r=0.80, P<0.001) but negatively with soil moisture (n=180, r=0.79, P<0.001) and net N-mineralization rates (n=180, r=0.92, P<0.0001). The higher N-mineralization and MB-N in the soil of forest ecosystem was reported compared to savanna and cropland and the order of soil MB-N levels and net N-mineralization followed the sequence: forest (sal) > mixed forest > savanna > cropland.
Ammonium transport in nitrogen-fixing cyanobacterium nostoc muscorum: Interaction with copper and sulfhydryl agents
(1984) A.K. Kashyap; Geeta Johar
Ammonium (NH4+) uptake in the cyanobacterium Nostoc muscorum ISU (Anabaena ATCC 27893) and interaction of copper (Cu2+) and sulfhydryl agents was studied. N2-grown cells scavenged extracellular NH4+via two energy-dependent transport systems: the ‘high-’ (Km= 11 μM, Vmax=0.22 nmol/min/mg protein) and ‘low-affinity’ (Km=66 μM, Vmax=1.25 nmol/min/mg protein). Both transport systems were competitively inhibited by methylamine (high-affinity Kt=20 μM; low affinity Kt=80 μM), and showed distinct pH profiles. Addition of Cu2+(0.1 μM) stimulated NH4+uptake by the high-affinity system (Km=8 μM, vmax= 0.42 nmol/min/mg protein). Similar effect was not observed with other bivalent cations (Hg2+, Ni2+, Zn2+, Mn2+) applied at equimolar concentrations. The sulfhydryl reducing agents, cysteine and dithiothreitol, inhibited the high-affinity system noncompetitively and caused efflux of accumulated NH4+. Cu2+eliminated the inhibitory effect of sulfhydryl reducing agents on NH4+uptake. Inhibition of NH4+uptake by sulfhydryl blocking agents (N-ethylmaleimide or p-chloromercuri-benzoate) which was not reversible by Cu2+suggested that oxidation of available sulfhydryl residues of membrane proteins (carriers) is an important factor in NH4+translocation in Nostoc muscorum. © 1984, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.
Ammonium Transport in the Alkalophilic Diazotrophic Cyanobacterium Nostoc calcicola: Influence of Phosphate Limitation and Metabolic Inhibitors
(1991) Poonam Prasad; A.K. Kashyap
Ammonium transport in the diazotrophic cyanobacterium Nostoc calcicola was investigated in phosphate-sufficient and deficient conditions. Cells grown under phosphate-deficient conditions were characterized by a decrease in specific growth rate, phycocyanin content (50 %), oxygen evolution (50 %), reduced ATP pool and derepressed alkaline phosphatase activity. Under these conditions ammonium transport exhibited no change in Km (10.0 µM) in comparison to phosphate-sufficient cells, but a change in Vmax (41.0 nmol mg-1 protein min-1) was observed. The reduced rate of ammonium transport was attributed to unavailability of sufficient energy. Conditions that lowered or abolished the ATP pool (dark incubation or treatment with metabolic inhibitors DCMU, DCCD or CCCP) also reduced ammonium transport via two transport systems. The results indicated that unavailability of phosphate in the immediate environment may limit ammonium transport by a diazotrophic cyanobacterium. © 1991, Gustav Fischer Verlag, Stuttgart. All rights reserved.
Ammonium Transport in Thermophilic Cyanobacterium Synechococcus Elongatus
(1990) Poonam Prasad; A.K. Kashyap
Ammonium (NH4) transport in the thermophilic, unicellular, non-nitrogen fixing cyanobacterium Synechococcus elongatus exhibited only one transport system (Km = 37.03 UM, Vmax = 250 nmol mg-1 protein min-1). A tenfold concentration gradient was established following 10 min of incubation in 60 jj,u NH4. The rate of NH4 transport was optimum at 50°C but no transport occurred at or below 30°C. Irreversible inactivation of the transport process occurred following exposure of the cells to 70°C. An Arrhenius plot of NH4 uptake (35-50°C) showed that an activation energy of 20.9 kcal/mol was required. The results suggested that the inability of the thermophilic cyanobacterium to grow at lower temperature could be due to unavailability of nutrients. © 1990, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.
Ammonium Transport in Unicellular Cyanobacterium Anacystis nidulans
(1985) A.K. Kashyap; Devendra P. Singh
Anacystis nidulans IU 625, grown on nitrate, has been shown to possess two ammonium (NH+4) uptake systems; the high- (Km = 50 μM, Vmax = 2 nmol min−1 mg−1 protein) and low-affinity (Km = 357 μM, Vmax = 10 nmol min−1 mg−1 protein) systems. The two uptake systems were specific for NH+4 since methylamine competitively inhibited both the uptake systems (high-affinity K1 = 100 μM, low-affinity Ki = 833 μM). The pH profile of the uptake systems suggested that the high-affinity system was maximally operative at pH 7.4 and the low affinity system at pH 5.2. The low affinity system was suppressed in cells grown on nitrate or ammonium while the high-affinity system was not completely repressed (52 and 36 % respectively). Both the transport systems were light-dependent and sensitive to DCMU. Effect of other metabolic inhibitors (DCCD, HOQNO, NEM) revealed that energy generated as a result of ATP hydrolysis was more important for NH+4 uptake by the low-affinity system, whilst the high-affinity system was more sensitive to protonophore FCCP suggesting an involvement of proton gradient of membrane. Concentrations of MSX non-inhibitory to GS activity during the course of experimentation showed mixed type inhibition of NH+4 uptake by the high-affinity system and non-competitive inhibition of the low-affinity system. Mutant A. nidulans/Mn 10 showed only one high-affinity system (Km = 250 μM, Vmax = 10 nmol min−1 mg−1 protein) maximally operative at pH 7.4, comparable to the lowaffinity system of the wild type. It is concluded that NH+4 uptake in A. nidulans is genetically controlled. © 1985, Gustav Fischer Verlag, Stuttgart. All rights reserved.
An assessment of biopotential of three cyanobacterial isolates from Antarctic for carotenoid production
(2003) S.P. Shukla; A.K. Kashyap
Specific growth rates and carotenoid contents of three Antarctic and tropical strains of cyanobacteria viz. Anabaena sp., Phormidium sp. and Nostoc sp. were compared in batch and mass cultures to assess bio-potential of Antarctic strains for cost-effective carotenoid production. Antarctic strains though exhibited slightly lower specific growth rates, but contained higher carotenoid contents (per unit dry wt.), than tropical strains. Modification of normal composition of BG-11 culture medium, by altering nitrogen and carbon sources resulted in 25-38% increase in carotenoid content in both types of strains. Mass-culture in indoor and semi- outdoor bio-reactors resulted in 39-113% higher carotenoid content in Antarctic strains, compared to their respective tropical strains. The observations suggest that Antarctic cyanobacteria may have potential as superior strains for maximizing the yield of carotenoids.
Antarctic cyanobacteria as a source of phycocyanin: An assessment
(2008) S.P. Shukia; Jay S. Singh; S. Kashyap; D.D. Giri; A.K. Kashyap
The growth characteristics and phycocyanin contents were examined in antarctic and tropical isolates of three cyanobacterial genera Anabaena, Nostoc and Phormidium in batch cultures, and in indoor and outdoor mass-culture units under varying conditions of temperature, light and nutrients. The Antarctic isolates showed 54-62% higher phycocyanin content than the tropical ones. The contents recorded in Antarctic isolates were 1.8 to 3.3 folds higher than the reported values for one of the commercially used strain of Spirulina maxima. The study proves that Antarctic cyanobacteria can yield higher amount of phycocyanin by manipulating growth conditions. The information will serve as a base line data for future biotechnological applications of antarctic cyanobacterial strains within the preview of the Antarctic treaty.
Changes in photoelectron transport activity in cyanophage N-1-infected cells of Nostoc muscorum
(Springer-Verlag, 1989) A.K. Kashyap; Surendra Singh
Cyanophage N-1-infected Nostoc muscorum cells were unable to carry out oxygen evolution and photosystem-II-dependent electron transport (H2O→DCPIP). This was associated with preferential degradation of phycobiliproteins. Such cells also exhibited decreased rate of ferredoxin:NADP+ oxidoreductase activity. However, Ca2+-dependent ATPase activity was maintained at a higher level (80%). The results suggested that virus development proceeds in the absence of photosystem-II activity, and the energy is provided by cyclic photophosphorylation aside from that possibly obtained via degradation of carbohydrate reserves. © 1989 Springer-Verlag New York Inc.
Characteristics and Regulation of the Ammonium Transport System in Filamentous Nonheterocystous Cyanobacterium Plectonema boryanum
(1995) A.K. Kashyap; Naz Shaheen; Poonam Prasad
Ammonium transport in Pectonema boryanum, a filamentous noneterocystous cyanoacterium was investigated in cells exposed to N-sufficient (medium with nitrate) or N-stress (medium without nitrate) conditions. T N-sufficient cells exhibited a single transport system (Km = 20 μM; Vmax = 258 mmol kg-1 protein min-1) and a 40-fold concentration gradient was formed following 10 min of transport. The transport was maximally operative at pH 7.0 and 33°C. The transport was not inhibited by methylamine (Km= 33.3 μM; Vmax=50 mmol kg-1 protein min-1). Following transfer o N-sufficient cells to N-stress conditions, the intracellular ammonium pool declined from 0. 38 to 0. 16 mM during the initial value during the first 6 h, but resumed to the initial value during the next 48 h. The N-stressed cells exhibited two ammonium transport systems with 〈high〉 and ⎒low affinity〉 respectively. The kinetics of the former system was similar to the N-sufficient cells, while the latter system had altered kinetics (Km = 50 μM; Vmax = 650 mmol kg-1 protein min-1). The results suggest that P. boryanum possesses multiple transport systems, and that their expression is regulated, depending upon the presence or absence of nitrate in the growth medium. © 1994, Gustav Fischer Verlag, Stuttgart. All rights reserved.
Characteristics of Ammonium Transport in an Alkalophilic Diazotrophic Cyanobacterium Nostoc calcicola: Influence of Temperature and Methionine Sulfoximine
(1990) Poonam Prasad; A.K. Kashyap
Ammonium transport in nitrogen fixing cyanobacterium Nostoc calcicola showed the existence of two ammonium-specific transport systems: (a) high-affinity (Km = 10 µM, Vmax = 50 nmol · mg-1 protein · min-1), and (b) low-affinity (Km = 200 µM, Vmax = 500 nmol · mg-1 protein · min-1). Experiments on pH profile showed that the former system was maximally operative at pH 6.0 and the latter at pH 7.0. Following 10 min of NH4 uptake, 16- and 75-fold concentration gradients were formed by high- and low-affinity systems, respectively, and formation of an intracellular NH4+ pool was independent of glutamine synthetase activity. Investigations on temperature profile revealed that the optimal temperature for the high-affinity system was 30 °C and for the low-affinity system was 40 °C. Discontinuities in the slopes of the Arrhenius plot for the two transport systems suggested that a 2.5-fold higher activation energy was required for the low-affinity system than the high-affinity system. Shift-down (50° → 30 °C) experiments revealed that irreversible inactivation of the transport process occurred following exposure to critical temperature. Inhibition of NH4+ transport by higher temperature and chloramphenicol suggested involvement of a proteinaceous carrier(s) in the process. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.
Contrasting pattern of methane flux in rice agriculture
(1998) Smita Singh; J.S. Singh; A.K. Kashyap
[No abstract available]
Contrasting pattern of methanotrophs in dry tropical forest soils: Effect of soil nitrogen, carbon and moisture
(Elsevier GmbH, 2007) J.S. Singh; A.K. Kashyap
Population dynamics of methane-oxidizing bacteria (MOB) was measured for 2 consecutive years for four forest and one savanna sites in seasonally dry tropical regions of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of soils. There were significant differences in MOB population size during the 2 years (mean 0.40 and 0.48×105 cells g-1 dry soil), and at different sites (mean 0.38-0.59×105 cells g-1 dry soil). The mean population size of MOB was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and MOB population size during summer (the driest period) and a negative relation during the rest of the year. The number of MOB was consistently higher for the Kotwa hill base site than rest of the sites having higher soil organic C and total N. The results suggested that in seasonally dry tropical forests the moisture, C and N status of the soil regulates the population size of MOB (methanotrophs) in the long term. © 2006 Elsevier GmbH. All rights reserved.
Cyanobacteria in Antarctica: ecology, physiology and cold adaptation.
(2004) K.D. Pandey; S.P. Shukla; P.N. Shukla; D.D. Giri; J.S. Singh; P. Singh; A.K. Kashyap
Cyanobacterial species composition of fresh water and terrestrial ecosystems and chemical environment of water in Schirmacher Oasis in Continental Antarctica was investigated. Over 35 species of cyanobacteria were recorded. Diazotrophic species both heterocystous and unicellular contributed more than half to the count except in lake ecosystem. The species composition varied among the fresh water as well as terrestrial ecosystems. The physico-chemical analyses of water revealed its poor nurient content which might have supported the growth of diazotrophic cyanobacteria in an Antarctic environment. Among the cyanobacteria Oscillatoria, Phormidium and Nostoc commune were the dominant flora in most of the habitats. The physiological characteristics of isolated cyanobacteria strains indicated that N2-fixation, nitrate uptake, nitrate-reduction, ammonium-uptake, GS-transferase activity and photosynthesis was unaffected at low temperature (5 degrees C) which indicated low temperature adaptation for Antarctic cyanobacteria. This phenomenon was not evident in different strains of tropical origin. The temperature optima for N2-fixation for the different Antarctic cyanobacterial strains was in the range of 15-25 degrees C, nearly 10 degrees C lower than their respective reference strains of tropical origin. Similar results were obtained for cyanobacteria-moss association. The low endergonic activation energy exhibited by the above metabolic activities supported the view that cyanobacteria were adapted to Antarctic ecosystem.
Differential sensitivity of three cyanobacteria to the rice field herbicide Machete
(1986) K.D. Pandey; A.K. Kashyap
The effect of the rice field herbicide Machete (2‐chloro‐2′6′‐diethyl‐N‐(Butoxymethyl)acetanilide) on the growth and cell composition of Anacystis nidulans, Nostoc muscorum and Anabaena doliolum was investigated. Growth of these cyanobacteria was completely inhibited at 2.5, 5.0 and 20 μg/ml, respectively, while a slight stimulation of growth was observed at lower concentrations. Stimulation of cyanobacterial growth in the presence of low concentrations of Machete was associated with an increase in the cellular levels of phycobilins and RNA while there was little impact on the levels of chlorophyll a and DNA. Photosynthetic pigments were degraded at lethal concentrations. The toxicity of the herbicide towards N. muscorum and A. doliolum could be reversed by supplementing the growth medium with either nitrate, nitrite or ammonia. This did not apply for A. nidulans. It is suggested that Machete inhibited nitrogen fixation in the former two strains while availability of nutrients was affected in the latter strain. In either case death of the organisms was most likely due to nitrogen starvation. Copyright © 1986 Wiley‐VCH
Dynamics of viable nitrifier community and nutrient availability in dry tropical forest habitat as affected by cultivation and soil texture
(Kluwer Academic Publishers, 1996) P.B. Jha; J.S. Singh; A.K. Kashyap
Seasonal dynamics of N-mineralization and the size of the viable community of nitrifying bacteria were studied for a forest site and an adjoining cropland site. The forest site was dominated by Boswellia serrata and Acacia catechu in the tree layer, and by Nyctanthes arbortristis and Zizyphus glaberrima in the shrub layer. Crop sequence on the cropland site was Oryza sativa/Lens culinaris. The soil type in both the sites was ultisol (USDA). The cropland soil had significantly higher bulk density, and clay content but lower organic C, total N and total P than forest soil. The soil moisture content, numbers of ammonia- and nitrite oxidizing bacteria and N- mineralization rates were highest in the wet season and lowest in the dry season, while the size of mineral N and P pools showed a reverse trend in both sites. The numbers of free-living cells of ammonia- and nitrite oxidizing bacteria were significantly related with each other as well as with the soil moisture content and N-mineralization rates. In N-mineralization, NO3/- was the dominating form in the forest site during rainy season, while in other seasons in this site and in all the seasons in the cropland site, NH4/+ -N was predominant. The N-mineralization rate and the number of viable nitrifying cells were consistently higher for the forest soil compared to the clay-rich cropland soil. The combination of low soil organic matter and high clay content suppressed the number of free-living cells of nitrifying bacteria and N-mineralization rates in the cropland site.
Dynamics of viable nitrifier community, N-mineralization and nitrification in seasonally dry tropical forests and savanna
(Elsevier GmbH, 2006) J.S. Singh; A.K. Kashyap
The study was conducted in Vindhyan region, to assess the N-mineralization, nitrification and size of viable community of ammonium- and nitrite-oxidizing bacteria as affected by different sites and seasons. Six different ecosystems (four forests and two savannas), which differ in terms of topography, vegetation and moisture status, were selected for the present study. The soils of the study sites differ significantly in its physico-chemical properties. The savanna site had significantly higher pH (7.2), bulk density (1.37 g cm-3) and silt content (67.80%) but lower water holding capacity (1.37%), total-C (16,356 μg g-1 dry soil), N (1090 μg g-1 dry soil) and P (213 μg g-1 dry soil) than forest sites. The soil moisture content, N-mineralization, nitrification rates and numbers of ammonium- and nitrite-oxidizing bacteria were highest in the wet season and lowest in dry season, while the size of mineral-N (NH4+ -N and NO 3- -N) showed a reverse trend at the sites. The N-mineralization, nitrification and nitrifier population size differ significantly across the site and season. The numbers of free-living cells of ammonium- and nitrite-oxidizing bacteria were significantly related to each other and to N-mineralization, nitrification, soil moisture and mineral-N components. The N-mineralization, nitrification and the viable number of nitrifying cells were consistently higher for forest soils compared to savanna sites. It was concluded that soil microbial process (N-mineralization and nitrification) and nitrifier population size were dependent on site topography, vegetation cover and soil moisture status. © 2005 Elsevier GmbH. All rights reserved.
Effect of cyanophage N-1 development on nitrogen metabolism of cyanobacterium Nostoc muscorum
(1988) A.K. Kashyap; A.N. Rai; Surendra Singh
The impact of cyanophage N-1 development on nitrogenase, glutamine synthetase (GS) and aminotransferases activities in the diazotrophic cyanobacterium Nostoc muscorum was investigated during its latent period. The nitrogenase activity was inhibited after 2 h of infection, suggesting that phage development does not require the product of nitrogenase activity. GS activity was not inhibited until 4 h of infection; however, a decline in activity was subsequently observed. Glutamate oxaloacetate transaminase was inhibited after 1 h of infection and no activity was detectable during the entire latent period. In contrast, glutamate pyruvate transaminase activity increased 2-fold by 4 h of infection and remained higher than the background level until the end of the latent period. The results suggested that under nitrogen fixing conditions, N-1 multiplication proceeds in the absence of nitrogen fixation and that the metabolism of amino acids is altered in favour of phage multiplication. © 1988.
Effect of fertilizer and organic matter inputs on nitrifier populations and N-mineralization rates in a dry tropical region, India
(1996) P.B. Jha; A.K. Kashyap; J.S. Singh
The study was conducted in a dryland farm, which was under Oryza sativa (rainy season)/Lens esculenta (winter seasons) crop rotation, to assess the size of viable community of ammonia- and nitrite-oxidizing bacteria and N-mineralization, as affected by season and inputs of chemical fertilizer and organic matter. Six treatments with three replicates were established in completely randomized block design. The treatments were: control, chemical fertilizer, wheat straw (WS), WS + fertilizer, farmyard manure (FYM) and FYM + fertilizer. The effects of treatments and seasons on NH+4-N, NO-3-N and PO-4-P pools were significant, but treatment X season interaction was not significant. The mineral N pools had a dry season maximum, while N-mineralization and nitrification rates were highest during rainy season and lowest during summer season. Differences in N-mineralization and nitrification rates due to treatments were significant. The N-mineralization rates were greatest in fertilizer and fertilizer + WS (or FYM) treatments and the nitrification rate was highest in the fertilizer treated soil. Analysis of pooled data of all treatments showed that N-mineralization rate was positively related with soil moisture and inversely with the size of mineral N pools. The numbers of viable cells of ammonia- and nitrite-oxidizing bacteria were related significantly to each other, and were highest during the rainy season and lowest in the summer season. The effect of treatments, except for the fertilizer-alone treatment, on the most probable number counts of the nitrifying bacteria was not statistically significant.
Effect of lethal copper concentrations on nitrate uptake, reduction and nitrite release in Anacystis nidulans.
(1982) A.K. Kashyap; S.L. Gupta
Results suggest that Cu2+ specifically inhibits at the level of nitrite assimilation. -from Authors
Effect of rice cultivars on rate of N-mineralization, nitrification and nitrifier population size in an irrigated rice ecosystem
(Elsevier, 2003) Paromita Ghosh; A.K. Kashyap
A study was conducted in irrigated rice fields planted to three rice (Oryza sativa) cultivars, Sarju-52, Malviya-36 and Pant Dhan-4, to investigate the influence of rice cultivars on rate of N-mineralization, nitrification and nitrifier population size. Thirty-day-old seedlings were transplanted in the waterlogged condition. Urea was the only fertilizer applied, at a rate of 100 kg N ha-1 in three split doses. The experiment was laid out in a randomized complete block design with three replicate plots for each cultivar and treatment. Soil mineral-N content, N-mineralization, nitrification and the most probable number of ammonium and nitrite oxidizing bacteria were estimated on six dates within the cropping period. It was observed that the mineral-N content in soil was lowest beneath Pant Dhan-4 under both unfertilized (control) and fertilized conditions. Mineral-N values in plots planted to Malviya-36 had intermediate values, while plots planted to Sarju-52 had highest mineral-N content under both control and fertilized conditions. Throughout the cropping season the lowest rate of N-mineralization, nitrification and nitrifier population was recorded in soil beneath Sarju-52 and highest beneath Pant Dhan-4. The highest vigour in terms of plant growth, grain yield and root porosity, was observed in Pant Dhan-4, followed by Malviya-36 and Sarju-52. Intercultivar differences in plant biomass production, which indicates the differences in nitrogen utilization potential and indirectly the quantity and quality of litter production may explain in part the differences in N-mineralization processes. The nitrifying bacterial population was strongly correlated with root biomass and root air space. The rice cultivars differed significantly in aerenchyma tissue differentiation resulting in different degrees of aerobic conditions in their rhizosphere. This explains the differences in nitrifier populations harboured by each of the cultivars in their respective soils and the consequent differences in soil processes. Hence, apart from fertilizer management, choice of rice cultivar also affects nitrifier populations and their functions, which are responsible for supplying nutrients to the rice soil. © 2003 Elsevier B.V. All rights reserved.