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Biodegradation of Linear Alkylbenzene Sulfonate (LAS) by Immobilized Pseudomonas sp.  [PDF]
Aju K. Asok, Pallickalvaliyaveettil Aboobaker Fathima, Manakulam Shaike Jisha
Advances in Chemical Engineering and Science (ACES) , 2015, DOI: 10.4236/aces.2015.54048
Abstract: Anionic surfactants are the most widely exploited chemical surfactants, which are being incorporated into majority of detergents and cleaning products used for household and industrial applications. Linear alkylbenzene sulfonates (LAS) is one of the major xenobiotic anionic surfactants. Biodegradation is an effective process to reduce the amount of surfactants released in the environment. In this study soil samples were collected from detergent contaminated sites to isolate linear alkylbenzene sulphonate degrading bacteria using mineral salt media supplemented with LAS as sole source of carbon. From the twenty isolates selected for the study, two of them (L9 and L12) have exhibited excellent ability to degrade LAS. The LAS degradation ability was determined by using MBAS assay and HPLC. The selected isolates were immobilized in alginate and polyvinyl alcohol to check the suitability of the isolates in onsite LAS removal. The percentage of degradation of LAS by alginate entrapped L9 was 85.155 ± 1.2 and that of PVA immobilized cells was 58.535 ± 2.9. Whereas L12 PVA entrapped were good compared to alginate. L12 exhibited 62.977 ± 1.3 percentage of degradation of LAS when immobilized in PVA and 61.07 ± 0.6 percentage in alginate entrapped condition. In comparison between the organisms alginate entrapped Pseudomonas nitroreducens (L9) was found to be superior to Pseudomonas aeruginosa (L12) in immobilised condition. It was found that immobilized cells performed superiorly than free cells. In particular, calcium alginate immobilised cells were more efficient in LAS removal than polyvinyl alcohol immobilised cells.
Assessment of Soil Microbial Toxicity on Acute Exposure of the Anionic Surfactant Linear Alkylbenzene Sulphonate
Aju K. Asok,M.S. Jisha
Journal of Environmental Science and Technology , 2012,
Abstract: The use of synthetic detergents is on increasing ladder due to shift from soaps to detergents. Linear Alkylbenzene Sulphonates (LAS) are one of the major anionic surfactant and used as active ingredients in household and personal care products. LAS may reach the soil environment due to its widespread use and disposal. In soil microcosm study LAS at different concentrations were added to the test soil and total bacterial, fungal and actinomycetes counts were recorded at different intervals. Bacteria showed high sensitivity to LAS exposure concentration, compared to fungi and actinomycetes. Soil dehydrogenase activity was also recorded and found that LAS treatment reduced dehydrogenase activity significantly. The correlation between heterotrophic bacterial count and dehydrogenase activity was done using a matrix of Pearson’s correlations coefficient. Though at lower concentrations a positive correlation was noted between the enzyme activity and bacterial count, at higher LAS concentrations a negative correlation was observed. Further studies are needed in order to evaluate the effects of LAS on soil quality.
Selenium Modulates Growth and Thiol Metabolism in Wheat (Triticum aestivum L.) during Arsenic Stress  [PDF]
Srijita Ghosh, Asok K. Biswas
American Journal of Plant Sciences (AJPS) , 2017, DOI: 10.4236/ajps.2017.83026
Abstract: Arsenic affects plants by disrupting their growth and metabolism while selenium, an essential micronutrient has beneficial role in stress tolerance. Owing to the antioxidative capacity of selenium, it can counteract detrimental effects of arsenic induced stress in plants. The interactive influence of arsenate and selenate on the growth, arsenic and selenium accumulation, activities of non-enzymatic and enzymatic antioxidants, levels of ascorbate, α-tocopherol, total glutathione and activities of glutathione regulatory enzymes along with characterization and quantification of phytochelatins in growing wheat (Triticum aestivum L.) seedlings were investigated. Rate of arsenic accumulation was increased in arsenate treated seedlings while in seedlings treated jointly with arsenate and selenate, arsenic accumulation decreased. Arsenate stress resulted decrease in ascorbate and total glutathione contents, activities of the glutathione metabolism enzymes while significantly increased the levels of α-tocopherol and phytochelatins (PC2 and PC4), along with activities of ascorbate peroxidase and ascorbic acid oxidase in the test seedlings. The effects were more pronounced in roots than in shoots. Joint application of arsenate along with selenate was able to overcome the adverse effects caused by arsenic alone to variable extents by exhibiting significant alterations of all parameters tested, imparting better growth and thiol metabolism in the test seedlings. Our results conclude that application of selenium fertilizer in arsenic contaminated soil might be favourable to improve growth and defense ability in wheat against arsenic toxicity.
Role of Flexible Macro Fibre Composite (MFC) Actuator on Bragg Wavelength Tuning in Microstructure Polymer Optical Fibre Long Period Grating for Strain Sensing Applications*  [PDF]
Asok K. Dikshit, Akhil Raj V. L.
Journal of Sensor Technology (JST) , 2013, DOI: 10.4236/jst.2013.33013
Abstract: The microstructure polymer optical fibre (mPOF) inscribed long period grating (LPG) offers a wide field of application in strain sensors arena within the materials elastic limit. Flexible innovative macro fibre composite (MFC) actuator generates electromechanical force under DC driving voltage. We propose a novel method for Bragg wavelength blue shifting through stretch tuning of mPOF LPG in axial direction under applied DC voltage on attached MFC with LPG. The grating period of mPOF LPG changes refractive index and causes blue shift of Bragg grating fibre wavelength. The shifting governs on the values of generated electromechanically strain transfer from flexible MFC to mPOF LPG and they have potential applications in strain sensor.
Regulation of Growth, Antioxidants and Sugar Metabolism in Rice (Oryza sativa L.) Seedlings by NaCl and Its Reversal by Silicon  [PDF]
Prabal Das, Paulin Seal, Asok K. Biswas
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.73055
Abstract: The effect of NaCl with or without silicon on the growth and metabolism in rice seedlings cv. MTU1010 was studied. In these seedlings, the oxidative stress has been observed with NaCl treatments and the levels of proline, H2O2 and malondialdehyde contents were increased whereas catalase activity was decreased. NaCl exposure at 25 mM, 50 mM and 100 mM concentrations in the test seedlings resulted in an increase in both reducing and non-reducing sugar content. There was a decrease in starch contents and the activity of starch phosphorylase was increased. NaCl stress also affected the activities of different carbohydrate metabolizing enzymes. The activities of sucrose synthase and sucrose phosphate synthase were increased, while the activity of acid invertase was decreased. Joint application of silicon with NaCl showed significant alterations on all parameters tested under the purview of NaCl treatment alone leading to better growth and metabolism in rice seedlings. Thus the use of silicon enriched fertilizers may help to grow healthy rice plants in NaCl rich soil.
Influence of Arsenate and Phosphate on the Regulation of Growth and TCA Cycle in the Rice (Oryza sativa L.) Cultivars IR64 and Nayanmani  [PDF]
Jayeeta Saha, Madhushree Dutta, Asok K. Biswas
American Journal of Plant Sciences (AJPS) , 2017, DOI: 10.4236/ajps.2017.88127
Abstract: The influence of arsenate and phosphate on the growth and respiration of 21 days old seedlings in two cultivars of rice, viz., IR64 and Nayanmani was studied. As arsenate and phosphate are similar in their chemical configuration and the latter is preferentially taken up by the phosphate transporters, it results in a competitive inhibition of arsenate uptake in presence of phosphate. Increasing concentrations of sodium arsenate (25 μM, 50 μM and 100 μM) hindered the growth in both the cultivars, with cv. IR64 being more severely affected than cv. Nayanmani. There was an elevation in the levels of organic acids measured in both the cultivars, accompanied by a reduction in the activities of the dehydrogenases of the TCA cycle, viz., pyruvate dehydrogenase, isocitrate dehydrogenase, succinate dehydrogenase and malate dedrogenase under arsenic treatment alone. Also, an elevation in the activities of citrate synthase and fumarase enzymes was noticed in both test seedlings with increasing concentrations of arsenic. These alterations were more prominent in cv. IR64 than in cv. Nayanmani. On joint application of phosphate along with arsenate, amelioration of the toxic effects of arsenate was observed to some extent, resulting in an overall revival of respiration leading to improved growth and metabolism.
Versatile Potentiality of Silicon in Mitigation of Biotic and Abiotic Stresses in Plants: A Review  [PDF]
Paulin Seal, Prabal Das, Asok K. Biswas
American Journal of Plant Sciences (AJPS) , 2018, DOI: 10.4236/ajps.2018.97105
Abstract: The “quasi-essential element” silicon (Si) is not considered indispensable for plant growth and its accumulation varies between species largely due to differential uptake phenomena. Silicon uptake and distribution is a complex process involving the participation of three transporters (Lsi1, Lsi2 and Lsi6) and is beneficial during recovery from multiple stresses. This review focuses on the pivotal role of silicon in counteracting several biotic and abiotic stresses including nutrient imbalances, physical stresses together with uptake, transport of this metalloid in a wide variety of dicot and monocot species. The knowledge on the beneficial effects of silicon and possible Si-induced mechanisms of minimizing stress has been discussed. Accumulation of silicon beneath the cuticles fortifies the cell wall against pathogen attack. Si-induced reduction of heavy metal uptake, root-shoot translocation, chelation, complexation, upregulation of antioxidative defense responses and regulation of gene expression are the mechanisms involved in alleviation of heavy metal toxicity in plants. Silicon further improves growth and physiological attributes under salt and drought stress. Effective use of silicon in agronomy can be an alternative to the prevalent practice of traditional fertilizers for maintaining sustainable productivity. Therefore, soil nutrition with fertilizers containing plant-available silicon may be considered a cost-effective way to shield plant from various stresses, improve plant growth as well as yield and attain sustainable cultivation worldwide.
Influence of Selenium on Growth, Antioxidants Production and Physiological Parameters of Rice (Oryza sativa L.) Seedlings and Its Possible Reversal by Coapplication of Sulphate  [PDF]
Debarati Das, Paulin Seal, Asok K. Biswas
American Journal of Plant Sciences (AJPS) , 2019, DOI: 10.4236/ajps.2019.1012158
Abstract: The effect of selenate (Na2SeO4) and sulphate (Na2SO4) was studied on growth and metabolism in two rice cultivars cv. satabdi and cv. khitish. Selenate at low concentration (2 μM) expressed growth promoting effect on rice seedlings as opposed to its high concentration (≥20 μM) where the test seedlings showed stunted growth with browning at the apices of both roots and shoots. The chlorophyll contents showed a dose dependent effect. Both chlorophyll a and chlorophyll b contents were inhibited with increase in selenate concentrations. The effect was more pronounced in cv. satabdi compared to cv. khitish.The level of accessory pigments w
Amplification or Reduction of Backscattering in a Coherently Amplifying or Absorbing Disordered Chain
Asok K. Sen
Physics , 1997, DOI: 10.1016/S0378-4371(98)00330-6
Abstract: We study localization properties of a one-dimensional disordered system characterized by a random non-hermitean hamiltonian where both the randomness and the non-hermiticity arises in the local site-potential; its real part being random, and a constant imaginary part implying the presence of either a coherent absorption or amplification at each site. While the two-probe transport properties behave seemingly very differently for the amplifying and the absorbing chains, the logarithmic resistance $u$ = ln$(1+R_4)$ where $R_4$ is the 4-probe resistance gives a unified description of both the cases. It is found that the ensemble-averaged $$ increases linearly with length indicating exponential growth of resistance. While in contrast to the case of Anderson localization (random hermitean matrix), the variance of $u$ could be orders of magnitude smaller in the non-hermitean case, the distribution of $u$ still remains non-Gaussian even in the large length limit.
Phase Distribution in a Disordered Chain and the Emergence of a Two-parameter Scaling in the Quasi-ballistic to the Mildly Localized Regime
Asok K. Sen
Physics , 1997, DOI: 10.1142/S0217984997000682
Abstract: We study the phase distribution of the complex reflection coefficient in different configurations as a disordered 1D system evolves in length, and its effect on the distribution of the 4-probe resistance $R_4$. The stationary ($L \to \infty$) phase distribution is almost always strongly non-uniform and is in general double-peaked with their separation decaying algebraically with growing disorder strength to finally give rise to a single narrow peak at infinitely strong disorder. Further in the length regime where the phase distribution still evolves with length (i.e., in the quasi-ballistic to the mildly localized regime), the phase distribution affects the distribution of the resistance in such a way as to make the mean and the variance of $log(1+R_4)$ diverge independently with length with different exponents. As $L \to \infty$, these two exponents become identical (unity). Obviously, these facts imply two relevant parameters for scaling in the quasi-ballistic to the mildly localized regime finally crossing over to one-parameter scaling in the strongly localized regime.
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