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RISS 인기검색어
- 검색키워드
- 저자 : Ware D. (검색결과 5 건)
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Utilization of Putrescine by Streptococcus pneumoniae During Growth in Choline-limited Medium
D. Ware,J. Watt,E. Swiatlo 한국미생물학회 2005 The journal of microbiology Vol.43 No.5
Polyamines such as putrescine are small, ubiquitous polycationic molecules that are required for optimal growth of eukaryotic and prokaryotic cells. These molecules have diverse effects on cell physiology and their intracellular content is regulated by de novo synthesis and uptake from the environment. The studies presented here examined the structure of a putative polyamine transporter (Pot) operon in Streptococcus pneumoniae (pneumococcus) and growth of pneumococci in medium containing putrescine substituted for choline. RT-PCR experiments demonstrated that the four genes encoding the Pot system are co-transcribed with murB, a gene involved in an intermediary step of peptidoglycan synthesis. Pneumococci grown in hemically-defined media (CDM) containing putrescine without choline enter logarithmic phase growth after 36-48 hs. However, culture density at stationary phase eventually reaches that of choline-containing medium. Cells grown in CDM-putrescine formed abnormally elongated chains in which the daughter cells failed to separate and the choline-binding protein PspA was no longer cell-associated. Experiments with CDM containing radiolabeled putrescine demonstrated that pneumococci concentrate this polyamine in cell walls. These data suggest that pneumococci can replicate without choline if putrescine is available and this polyamine may substitute for aminoalcohols in the cell wall teichoic acids.
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Utilization of Putrescine by Streptococcus pneumoniae During Growth in Choline-limited Medium
Ware D.,Watt J.,Swiatlo E. The Microbiological Society of Korea 2005 The journal of microbiology Vol.43 No.5
Polyamines such as putrescine are small, ubiquitous polycationic molecules that are required for optimal growth of eukaryotic and prokaryotic cells. These molecules have diverse effects on cell physiology and their intracellular content is regulated by de novo synthesis and uptake from the environment. The studies presented here examined the structure of a putative polyamine transporter (Pot) operon in Streptococcus pneumoniae (pneumococcus) and growth of pneumococci in medium containing putrescine substituted for choline. RT-PCR experiments demonstrated that the four genes encoding the Pot system are co-transcribed with murB, a gene involved in an intermediary step of peptidoglycan synthesis. Pneumococci grown in chemically-defined media (CDM) containing putrescine without choline enter logarithmic phase growth after 36-48 hs. However, culture density at stationary phase eventually reaches that of choline-containing medium. Cells grown in CDM-putrescine formed abnormally elongated chains in which the daughter cells failed to separate and the choline-binding protein PspA was no longer cell-associated. Experiments with CDM containing radiolabeled putrescine demonstrated that pneumococci concentrate this polyamine in cell walls. These data suggest that pneumococci can replicate without choline if putrescine is available and this polyamine may substitute for aminoalcohols in the cell wall teichoic acids.
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Evaluation of Neutron Cross Sections for Hafnium in the Resolved Resonance Range
T. Ware,D. Weaver,M. Moxon,C. Dean,R. Hiles,P. Schillebeeckx,S. Kopecky 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The international High Priority Request list notes: - "In the nuclear industry hafnium is used as neutron absorbing material to regulate the fission process. Interpretation of critical experiments with UOx fuel conducted by CEA in the AZUR zero-power reactors has shown systematic underestimation of the reactivity worth that may be attributed to an overestimated natural hafnium capture cross section in the epi-thermal energy range"To service the request for improved resonance data a PhD project has:-a) Improved REFIT R-matrix evaluation code.b) Obtained hafnium oxide samples enriched in Hf176, 177, 178, 179 isotopes.c) Gained support from NUDAME and EUFRAT projects.d) Prepared enriched and natural Hf samples.e) Performed capture and transmission Time of Flight measurements at the GELINA linear accelerator.f) Analysed the capture counts to generate yields using AGS and AGL codes.g) Used REFIT to perform least squares analysis of GELINA measurements.(Included previous ORNL, Harwell and RPI transmissions and capture yields.)h) Submitted results to EXFOR.i) Included resolved resonance parameters in JEFF evaluations taking the resolved range to over 1keV. j) Tested evaluations with suitable benchmarks.k) Passed resolved resonance data to CEA Cadarache for unresolved analysis.Resultant Hf evaluations will be included in JEFF3.2.
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Cellobiose Hydrolysis Using Acid-functionalized Nanoparticles
L. Peña,M. Ikenberry,B. Ware,K. L. Hohn,D. Boyle,X. S. Sun,D. Wang 한국생물공학회 2011 Biotechnology and Bioprocess Engineering Vol.16 No.6
Mineral acids have been used effectively for the pretreatment of cellulosic biomass to improve sugar recovery and promote its conversion to ethanol; however,substantial capital investment is required to enable separation of the acid, and corrosion-resistant materials are necessary. Disposal and neutralization costs are also concerns because they can decrease the economic feasibility of the process. In this work, three acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass. Silica-protected cobalt spinel ferrite nanoparticles were functionalized with perfluoroalkylsulfonic acid (PFS), alkylsulfonic acid (AS), and butylcarboxylic acid (BCOOH) groups. These nanoparticles were magnetically separated from the reaction media and reused. TEM images showed that the average diameter was 2 nm for both PFS and BCOOH nanoparticles and 7 nm for AS nanoparticles. FTIR confirmed the presence of sulfonic and carboxylic acid functional groups. Ion exchange titration measurements yielded 0.9, 1.7, and 0.2mmol H+/g of catalyst for PFS, AS, and BCOOH nanoparticles,respectively. Elemental analysis results indicated that PFS and AS nanoparticles had 3.1 and 4.9% sulfur,respectively. Cellobiose hydrolysis was used as a model reaction to evaluate the performance of acid-functionalized magnetic nanoparticles for breaking β-(1→4) glycosidic bonds. Cellobiose conversion of 78% was achieved when using AS nanoparticles as the catalyst at 175°C for 1 h,which was significantly higher than the conversion for the control experiment (52%). AS nanoparticles retained more than 60% of their sulfonic acids groups after the first run,and 65 and 60% conversions were obtained for the second and third runs, respectively.
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