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136 results on '"Ghosh Amar N"'

1. Cross-Phase Modulation Instability in PM ANDi Fiber-Based Supercontinuum Generation

Author

Genier, Etienne, Ghosh, Amar N., Bobba, Swetha, Bowen, Patrick, Moselund, Peter M., Bang, Ole, Dudley, John M., and Sylvestre, Thibaut

Subjects
Physics - Optics
Abstract

We demonstrate broadband supercontinuum generation in an all-normal dispersion polarization-maintaining photonic crystal fiber and we report the observation of a cross-phase modulation instability sideband that is generated outside of the supercontinuum bandwidth. We demonstrate this sideband is polarized on the slow axis and can be suppressed by pumping on the fiber's fast axis. We theoretically confirm and model this nonlinear process using phase-matching conditions and numerical simulations, obtaining good agreement with the measured data.

Published
2020
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2. Physicochemical characterization of vibriophage N5

Author

Sen Anindito and Ghosh Amar N

Subjects
Vibriophage N5, DNA, Vibrio cholerae, Electron Microscopy, Partial denaturation mapping, Bacteriophage, Infectious and parasitic diseases, RC109-216
Abstract

Abstract Phage N5 is one of the phages of Vibrio cholerae serovar O1 biotype El Tor (Ghosh, A. N., Ansari, M. Q., and Dutta, G. C. Isolation and morphological characterization of El Tor cholera phages. J. Gen. Virol. 70: 2241–2243, 1989). In the present communication the growth curve, molecular weight and confirmation of the genome, partial denaturation map and restriction endonuclease digestion pattern have been determined. Partial denaturation map indicates that the genome has non-permuted / invariant sequence. Presence of cohesive ends has also been documented.

Published
2005
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3. New Vibrio cholerae O1 Biotype ElTor bacteriophages

Author

Sen Anindito and Ghosh Amar N

Subjects
Vibrio, phage, Electron microscopy, Infectious and parasitic diseases, RC109-216
Abstract

Abstract We report the presence of three new O1 ElTor vibriophages named AS1, AS2 and AS3, isolated from the sewage and pond waters of the outskirts of Kolkata. A few phages, named AS4, with hexagonal heads and abnormally long tails with typical curly projections were also found in the water samples.

Published
2005
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4. Nanoimprinting and Tapering of Chalcogenide Photonic Crystal Fibers for Cascaded Supercontinuum Generation

Author

Petersen, Christian R., Lotz, Mikkel B., Woyessa, Getinet, Ghosh, Amar N., Sylvestre, Thibaut, Brilland, Laurent, Troles, Johann, Jakobsen, Mogens H., Taboryski, Rafael, and Bang, Ole

Subjects
Physics - Optics
Abstract

Improved long-wavelength transmission and supercontinuum (SC) generation is demonstrated by anti-reflective (AR) nanoimprinting and tapering of chalcogenide photonic crystal fibers (PCF). Using a SC source input spanning from 1-4.2 {\mu}m, the total transmission of a 15 {\mu}m core diameter PCF was improved from ~53 % to ~74 % by nanoimprinting of AR structures on both input- and output facets of the fiber. Through a combined effect of reduced reflection and red-shifting of the spectrum to 5 {\mu}m, the relative transmission of light >3.5 {\mu}m in the same fiber was increased by 60.2 %. Further extension of the spectrum to 8 {\mu}m was achieved using tapered fibers. The spectral broadening dynamics and output power was investigated using different taper parameters and pulse repetition rates., Comment: I have permission from OSA to publish the pre-print version of my paper here on arXiv as long as I include a copyright statement and link to the article. For verification please contact copyright@osa.org regarding manuscript 376382

Published
2019
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11. Recent progress in fiber-based supercontinuum sources

Author

Sylvestre, Thibaut, primary, Genier, Etienne, additional, Ghosh, Amar N., additional, Bowen, Patrick, additional, Genty, Goery, additional, Troles, Johann, additional, Mussot, Arnaud, additional, Peacock, Anna C., additional, Klimczak, Mariusz, additional, Heidt, Alexander M., additional, Travers, John C., additional, Bang, Ole, additional, and Dudley, John M., additional

Published
2022
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12. Three-dimensional structure of different functional forms of the Vibrio cholerae hemolysin oligomer: a cryo-electron microscopic study

Author

Dutta, Somnath, Mazumdar, Budhaditya, Banerjee, Kalyan K., and Ghosh, Amar N.

Subjects
Oligomers -- Observations, Cholera toxin -- Observations, Vibrio cholerae -- Physiological aspects, Biological sciences
Abstract

Vibrio cholerae hemolysin (HlyA) is a 65-kDa water-soluble pore-forming toxin that causes lysis of eukaryotic cells by destroying selective permeability of the plasma membrane bilayer. The HlyA monomer self-assembles on the target cell surface to the more stable [beta]-barrel amphipathic heptamer, which inserts into the membrane bilayer to form a diffusion channel. Deletion of the 15-kDa [beta]-prism lectin domain at the C terminus generates a 50-kDa hemolysin variant (HlyA50) with an ~1,000-fold decrease in hemolytic activity. Because functional differences are eventually dictated by structural differences, we determined three-dimensional structures of 65- and 50-kDa HlyA oligomers, using cryo-electron microscopy and single-particle methods. Our study clearly shows that the HlyA oligomer has sevenfold symmetry but that the HlyA50 oligomer is an asymmetric molecule. The HlyA oligomer has bowl-like, arm-like, and ring-like domains. The bowl-like domain is coupled with the ring-like domain, and seven side openings are present just beneath the ring-like domain. Although a central channel is present in both HlyA and HlyA50 oligomers, they differ in pore size as well as in shape of the molecules and channel. These structural differences may be relevant to the striking difference in efficiencies of functional channel formation by the two toxin forms. doi: 10.1128/JB.00930-09

Published
2010

16. 2–10 µm Mid‐Infrared Fiber‐Based Supercontinuum Laser Source: Experiment and Simulation

Author

Venck, Sébastien, primary, St‐Hilaire, François, additional, Brilland, Laurent, additional, Ghosh, Amar N., additional, Chahal, Radwan, additional, Caillaud, Céline, additional, Meneghetti, Marcello, additional, Troles, Johann, additional, Joulain, Franck, additional, Cozic, Solenn, additional, Poulain, Samuel, additional, Huss, Guillaume, additional, Rochette, Martin, additional, Dudley, John M., additional, and Sylvestre, Thibaut, additional

Published
2020
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17. Cascaded Fiber-based Mid-Infrared Supercontinuum Source

Author

Venck, Sébastien, primary, St-Hilaire, François, primary, Brilland, Laurent, primary, Ghosh, Amar N., primary, Chahal, Radwan, primary, Caillaud, Céline, primary, Meneghetti, Marcello, primary, Troles, Johann, primary, Joulain, Franck, primary, Cozic, Solenn, primary, Poulain, Samuel, primary, Huss, Guillaume, primary, Rochette, Martin, primary, Dudley, John M., primary, and Sylvestre, Thibaut, primary

Published
2020
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22. Prevalence of Shigella boydii in Bangladesh: Isolation and Characterization of a Rare Phage MK-13 That Can Robustly Identify Shigellosis Caused by Shigella boydii Type 1

Author

Akter, Mahmuda, primary, Brown, Nathan, additional, Clokie, Martha, additional, Yeasmin, Mahmuda, additional, Tareq, Tokee M., additional, Baddam, Ramani, additional, Azad, Muhammad A. K., additional, Ghosh, Amar N., additional, Ahmed, Niyaz, additional, and Talukder, Kaisar A., additional

Published
2019
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26. Newly isolated Vibrio cholerae non-O1, non-O139 phages

Author

Sarkar, B.L., Ghosh, Amar N., Sen, Anindito, and Rodrigues, D.P.

Subjects
Cholera
Abstract

To the Editor: The epidemic cholera caused by Vibrio cholerae O1 appeared in Latin America in 1991 after a 100-year absence. Following its explosive appearance in Peru, travelers on the [...]

Published
2004

30. The cyclic AMP (cAMP)-cAMP receptor protein signaling system mediates resistance of Vibrio cholerae O1 strains to multiple environmental bacteriophages

Author

Zahid, M. Shamim Hasan, Waise, Zaved, T.M., Kamruzzaman, M., Ghosh, Amar N., Nair, G. Balakrish, Mekalanos, John J., and Faruque, Shah M.

Subjects
Bacteriophages -- Genetic aspects, Bacteriophages -- Physiological aspects, Cholera -- Causes of, Cholera -- Research, Cyclic adenylic acid -- Chemical properties, Cyclic adenylic acid -- Structure, Transposons -- Research, Biological sciences
Abstract

A transposon insertion library of Vibrio cholerae O1 E1 Tor biotype strain C6706 was screened to identify bacterial genes involved in mediating the phage-resistant phenotype. The results revealed that cyclase or cyclic AMP-cAMP receptor protein (cAMP)-CRP-mediated downregulation of phage adsorption might contribute to a mechanism for the V. cholerae O1 strains to survive predation by multiple environmental phages and the cyaA or crp mutant strains might be used as suitable indicators to monitor cholera phages in the water.

Published
2010

35. Cryo-electron microscopy reveals the membrane insertion mechanism of V. cholerae hemolysin

Author

Dutta, Somnath, Banerjee, Kalyan K., and Ghosh, Amar N.

Abstract

Vibrio cholerae hemolysin (HlyA) is a 65 kDa pore-forming toxin which causes lysis of target eukaryotic cells by forming heptameric channels in the plasma membrane. Deletion of the 15 kDa C-terminus β-prism carbohydrate-binding domain generates a 50 kDa truncated variant (HlyA50) with 1000-fold-reduced pore-forming activity. Previously, we showed by cryo-electron microscopy that the two toxin oligomers have central channels, but the 65 kDa toxin oligomer is a seven-fold symmetric structure with bowl-, ring-, and arm-like domains, whereas the 50 kDa oligomer is an asymmetric jar-like heptamer. In the present study, we determined three-dimensional(3D) structures of HlyA and HlyA50 in presence of erythrocyte stroma and observed that interaction of the 65 kDa toxin with the stroma induced a significant decrease in the height of the β-barrel oligomer with a change in conformation of the ring- and arm-like domains of HlyA. These features were absent in interaction of HlyA50 with stroma. We propose that this conformational transition is critical for membrane-insertion of the toxin.

Published
2014
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37. Preliminary Characterization of El Tor Vibriophage M4.

Author

Das, Sayani and Ghosh, Amar N.

Subjects
*BACTERIOPHAGES, *BACTERIAL genomes, *EFFECT of heat on bacteria, *BACTERIA morphology, *ELECTRON microscopy
Abstract

Aims: The aim of the present study is the preliminary characterization of an El Tor vibriophage M4 (ATCC 51352-B4). Methods: We studied the growth characteristics and sustainability of this phage under various stresses like temperature, pH, and UV. The phage morphology and phage genome were also examined using electron microscopy. Results: Sustainability studies showed that the phage is more stable in acidic conditions, which is very uncommon among vibriophages. Studies also showed that M4 is a thermostable phage and it is inactivated by temperatures above 60°C but, like other phages, UV has a high inactivating effect on it. Morphological and genomic studies by electron microscopy showed that this phage has a long contractile tail and a big head. The genome is linear and about 120 kb in length. The genome also has a high packaging density as the value of Vm (the volume occupied per Da of biological macromolecule) is low for this phage. The phage-bacterial interaction was studied by negative staining as well as ultrathin sectioning methods. Conclusions: M4 belongs to the Myoviridae family and it is generally thermostable. It is prone to destruction by alkali and UV. It also has a large DNA which is densely packed inside of a big capsid. [ABSTRACT FROM AUTHOR]

Published
2018
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41. Visualizing a Vibrio choleraeO1 El Tor typing bacteriophage belonging to the Myoviridae group and the packaging of its genomic ends inside the phage capsid

Author

Sen, Anindito and Ghosh, Amar N.

Abstract

Phage D10, an O1 El Tor tying vibriophage, has been successfully employed to tract the outspread of cholera epidemic. Using Transmission Electron Microscopy and computational image analysis, we have determined the structures of the capsid, head-to-tail connector, the contractile helical tail, the baseplate and combined them to form the complete three-dimensional (3D) D10 phage structure. Using partial denaturation experiments on the genome and using the computed 3D structure of the phage, we have established the packing of the genome ends inside the capsid together with the release styles during the phage infection, respectively. Finally, using the 3D density maps of the different components of the D10 phage, we have presented a simplified picture of morphogenesis of the D10 vibriophage. Using the complete assembled structure of the D10 phage, we have traced the path of the phage genome during the infection process, all the way from the phage head down the tail tube of the tail to the top of the baseplate. To the best of our knowledge, this is first structural study for a long-tailed vibriophage. We have tabulated the structural features of the different components of the phages belonging to the Myoviridae and Siphoviridae. The comparative study suggested the possibility of a common origin of the bacteriophages, irrespective of belonging to different groups and species.

Published
2018
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