The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Sunghoon Park - One of the best experts on this subject based on the ideXlab platform.
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development of a recombinant escherichia coli based biocatalyst to enable high styrene epoxidation activity with high product yield on energy source
Process Biochemistry, 2010Co-Authors: Seunghee Shin, Yongjoo Jeong, Jinbyung Park, Sunghoon ParkAbstract:Abstract A highly active recombinant whole-cell biocatalyst, Escherichia coli pETAB2/pG-KJE1, was developed for the efficient production of (S)-styrene oxide from styrene. The recombinant E. coli overexpressed styAB the genes of styrene monooxygenase of Pseudomonas putida SN1 and coexpressed the genes encoding chaperones (i.e., GroEL–GroES and DnaK–DnaJ–GrpE). The styrene monooxygenases were produced to ca. 40% of the total soluble proteins, enabling the whole-cell activity of the recombinant of 180 U/g CDW. The high StyAB activity in turn appeared to direct cofactors and molecular oxygen to styrene epoxidation. The product yield on energy source (i.e., glucose) reached ca. 40%. In addition, biotransformation in an organic/aqueous two-liquid phase system allowed the product to accumulate to 400 mM in the organic phase within 6 h, resulting in an average specific and volumetric productivity of 6.4 mmol/g Dry Cells/h (106 U/g Dry Cells) and 67 mM/h (1110 U/L aq ), respectively, under mild reaction conditions. These results indicated that the high productivity and the high product yield on energy source were driven by the high enzyme activity. Therefore, it was concluded that oxygenase activity of whole-cell biocatalysts is one of the critical factors to determine their catalytic performance.
R.m. Amer - One of the best experts on this subject based on the ideXlab platform.
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Cadmium biosorption by a cadmium resistant strain of Bacillus thuringiensis: regulation and optimization of cell surface affinity for metal cations
Biometals, 2000Co-Authors: E.r. El-helow, S.a. Sabry, R.m. AmerAbstract:A marine bacterial strain putatively identified as Bacillus thuringiensis strain DM55, showed multiple heavy metal resistance and biosorption phenotypes. Electron microscopic studies revealed that DM55 Cells are encased in anionic cell wall polymers that can immobilize discrete aggregates of cations. Factors affecting cell surface affinity for metal cations, monitored by means of Cd^2+ binding capability, are investigated. The mechanisms of cadmium resistance and Cd^2+ biosorption by the bacterium appeared to be inducible and coincident. Medium components affecting metal removal under cadmium-stressed growth conditions were explored based on the application of two sequential multi-factorial statistical designs. Concentrations of potassium phosphates and peptone were the most significant variables. Optimized culture conditions allowed DM55 Cells grown in the presence of 0.25 mM CdCl_2 to remove about 79% of the metal ions within 24 h with a specific biosorption capacity of 21.57 mg g^−1 of biomass. Both fresh and Dry Cells of DM55 prepared under cadmium-free optimal nutrient condition were also able to biosorb Cd^2+. In addition to the concentration of phosphate in the medium, KinA, a major phosphate provider in the phosphorelay of Bacillus Cells, was also demonstrated to regulate the magnitude of cell surface affinity for cadmium ions.
Hakan Basagaoglu - One of the best experts on this subject based on the ideXlab platform.
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robust representation of Dry Cells in single layer modflow models
Ground Water, 2008Co-Authors: S L Painter, Hakan BasagaogluAbstract:: Dewatered or "Dry" grid Cells in the USGS ground water modeling software MODFLOW may cause nonphysical artifacts, trigger convergence failures, or interfere with parameter estimation. These difficulties can be avoided in two dimensions by modifying the spatial differencing scheme and the iterative procedure used to resolve nonlinearities. Specifically, the spatial differencing scheme is modified to use the water level on the upstream side of a pair of adjacent Cells to calculate the saturated thickness and hence intercell conductance for the pair. This makes it possible to explicitly constrain the water level in a cell to be at or above the cell bottom elevation without introducing nonphysical artifacts. Thus constrained, all initially active Cells will remain active throughout the simulation. It was necessary to replace MODFLOW's Picard iteration method with the Newton-Raphson method to achieve convergence in demanding applications involving many Dry Cells. Tests using a MODFLOW variant based on the new method produced results nearly identical to conventional MODFLOW in situations where conventional MODFLOW converges. The new method is extremely robust and converged in scenarios where conventional MODFLOW failed to converge, such as when almost all Cells dewatered. An example application to the Edwards Aquifer in south-central Texas further demonstrates the utility of the new method.
Alex Rapoport - One of the best experts on this subject based on the ideXlab platform.
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Resistance of a recombinant Escherichia coli to dehydration
Cell Biology International, 2009Co-Authors: G. Khroustalyova, Joseph Boudrant, Alex RapoportAbstract:Dehydration of microorganisms, rendering them anhydrobiotic, is often an efficient method for the short and long term conservation of different strain-producers. However, some biotechnologically important recombinant bacterial strains are extremely sensitive to conventional treatment. We describe appropriate conditions during dehydration of the recombinant Escherichia coli strain HB 101 (GAPDH) that can result Dry Cells having a 88% viability on rehydration. The methods entails air-Drying after addition of 100 mM trehalose to the cultivation medium or distilled water (for short term incubation).
Gottfried Unden - One of the best experts on this subject based on the ideXlab platform.
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changes in the proton potential and the cellular energetics of escherichia coli during growth by aerobic and anaerobic respiration or by fermentation
FEBS Journal, 1998Co-Authors: Quang Hon Tran, Gottfried UndenAbstract:The energetic parameters of Escherichia coli were analyzed for the aerobic/anaerobic transition. The electrochemical proton potential (Δ p) across the cytoplasmic membrane was determined in the steady state of respiration with O2, nitrate, fumarate, dimethylsulfoxide (Me2SO), and for fermentation. With O2, a proton potential of −160 mV was obtained. For anaerobic respiration with nitrate, fumarate or Me2SO, Δ p decreased only slightly by about 20 mV in contrast to earlier assumptions, whereas Δ p dropped by approximately 40 mV during fermentation. Under all conditions, the membrane potential (Δ @KY) contributed the major portion to Δ p. The cellular ATP levels were highest for aerobic growth (about 13 μmol/g Dry Cells) and decreased to 3−6 μmol/g in anaerobic metabolism. Δ .cf2.G.cf2..cf1..es.cf1.′.cf5..rb.eiPhos.rb, however, was constant due to equivalent changes of the ADP contents. Transition to the stationary growth phase caused a massive drop in the ATP content. It is concluded that, during anaerobic respiration, the energetic situation for the bacteria is very similar to that for aerobic growth with respect to Δ .cf2.G.cf2..cf1..es.cf1.′.cf5..rb.eiPhos.rb and Δ p whereas, for fermentation, a significant decrease in Δ p was observed. The consequences for the cellular energetics and for the regulation of the aerobic/anaerobic transition are discussed.
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dmso respiration by the anaerobic rumen bacterium wolinella succinogenes
Archives of Microbiology, 1994Co-Authors: Jurgen Lorenzen, Swantje Steinwachs, Gottfried UndenAbstract:The anaerobic rumen bacterium Wolinella succinogenes was able to grow by respiration with dimethylsulphoxide (DMSO) as electron acceptor and formate or H2 as electron donors. The growth yield amounted to 6.7 g and 6.4 g Dry Cells/mol DMSO with formate or H2 as the donors, respectively. This suggested an ATP yield of about 0.7 mol ATP/mol DMSO. Cell homogenates and the membrane fraction contained DMSO reductase activity with a high Km (43 mM) for DMSO. The electron transport from H2 to DMSO in the membranes was inhibited by 2-(heptyl)-4-hydroxyquinoline N-oxide, indicating the participation of menaquinone. Formation of DMSO reductase activity occurred only during growth on DMSO, presence of other electron acceptors (fumarate, nitrate, nitrite, N2O, and sulphur) repressed the DMSO reductase activity. DMSO can therefore be used by W. succinogenes as an acceptor for phosphorylative electron transport, but other electron acceptors are used preferentially.
