1,721,210 research outputs found
Metabolic flux analysis for succinic acid production by recombinant Escherichia coli with amplified malic enzyme activity
No full textA pfl IdhA double mutant Escherichia coil strain NZN111 was used to produce succinic acid by overexpressing the E. coli malic enzyme. Escherichia coli strain NZN111 harboring pTrcML produced 6 and 8 g/L of succinic acid from 20 g/L of glucose in flask culture at 37 degreesC and 30 degreesC, respectively. When NZN111(pTrcML) was cultured at 30 degreesC with intermittent glucose feeding the final succinic acid concentration obtained was 9.5 g/L and the ratio of succinic acid to acetic acid was 13:1. This system could not be analyzed by conventional metabolic flux analysis techniques, since some pyruvate and succinic acid were accumulated intracellularly. Therefore, a new flux analysis method was proposed by introducing intracellular pyruvate and succinic acid pools. By this new method the concentrations of intracellular metabolites were successfully predicted and the differences between the measured and calculated reaction rates could be considerably reduced. (C) 2001 John Wiley & Sons, Inc.We thank David P. Clark for kindly providing the E. coli strain
NZN111. We also thank J. Villadsen for many important suggestions
regarding the metabolic flux analysis
Importance of redox balance on the production of succinic acid by metabolically engineered Escherichia coli
No full textWe had previously shown that succinic acid production in a pfl ldhA double mutant strain of Escherichia coli could be enhanced by amplifying the malic enzyme activity. However, recombinant E. coli NZN111 (F- Deltapfl::Cam ldhA::Kan) harboring pTrcML, a plasmid containing the E. coli malic enzyme gene, produced a considerable amount of malic acid along with the desired product, succinic acid. To have an insight into the intracellular metabolism, metabolic control analysis was carried out. From the results of a simulation, it was predicted that supplying additional reducing power could enhance succinic acid production. More reduced carbon substrate sorbitol was thus examined for the possibility of matching the potential during succinic acid production. When NZN111 (pTrcML) was cultured in LB medium containing 20 g sorbitol/l under a CO2 atmosphere, 10 g succinic acid/l was produced. The apparent yield of succinic acid was 1.1 g succinic acid/g sorbitol, which is 85% of the maximum theoretical yield. Therefore, it was found that redox balancing was important for the enhanced production of succinic acid in metabolically engineered E. coli.We thank David P. Clark for kindly providing
us with the E. coli strain NZN111. This work was supported
by the National Research Laboratory Program (2000-N-NL-01-C-
237) of the Korean Ministry of Science and Technology
Metabolic flux distribution in a metabolically engineered Escherichia coli strain producing succinic acid
No full textEscherichia coli NZN111, which is known as a pfl ldhA double mutant strain, was metabolically engineered to produce succinic acid by overexpressing melic enzyme into the E. coli controlled by a trc promoter. Fermentation studies were carried out in a LB medium by first growing cells aerobically to an OD600 of 5. At this point, 0.01 mM IPTG was added to induce the overexpression of malic enzyme and the agitation speed was gradually lowered. When the culture OD600 reached 11, a complete anaerobic condition was achieved by flushing with a CO2-H-2 gas mixture. When NZN111 (pTrcML) was cultured at 37 degrees C, the final succinic acid concentration of 2.8 g/l could be obtained after 30 h of anaerobic cultivation. The fermentation results were analyzed by the calculation of metabolic fluxes. Metabolic flux analysis showed that about 85% of phosphoenolpyruvate (PEP) was converted to pyruvate. and further converted to malic acid by melic enzyme.We thank David P. Clark for kindly providing us with the E.coli strain NZN111. This work was supported by the Ministry of Science and Technology (MOST)
Joint video coding of MPEG-2 video programs for digital broadcasting services
No full textIn digital broadcasting services such as digital satellite TV, cable TV, and digital terrestrial TV, several video programs are compressed by MPEG-2 and then simultaneously transmitted over a conventional CBR (Constant Bit Rate) broadcasting channel, In this environment, picture quality of the aggregated video programs should be kept as equal as possible to provide fare video services for all the viewers. In this paper we propose a joint video coding scheme for ensuring that picture quality of all the programs are nearly the same. This objective is achieved by simultaneously controlling the video encoders to generate the VER (Variable Bit Rate) compressed video streams. This paper contributes in two ways, First, we propose a rate-distortion estimation method for MPEG-2 video, which enables us to predict the amount of bits and the distortion generated from an encoded picture at a given quantization step size and vice versa. The most attractive features of the proposed estimation method are its accuracy and a computational complexity low enough to be applied to real-time video coding applications. Second, this paper presents an efficient and accurate joint video coding scheme using the rate-distortion estimation results. The experimental results show that our coding scheme gives higher and more stable picture quality and more efficient channel utilization than an independent coding scheme that encodes each program independently
Elucidation of Multifaceted Evolutionary Processes of Microorganisms by Comparative Genome-Based Analysis
No full textThe evolution of living organisms occurs via a combination of highly complicated processes that involve modification of various features such as appearance, metabolism and sensing systems. To understand the evolution of life, it is necessary to understand how each biological feature has been optimized in response to new environmental conditions and interrelated with other features through evolution. To accomplish this, we constructed contents-based trees for a two-component system (TCS) and metabolic network to determine how the environmental communication mechanism and the intracellular metabolism have evolved, respectively. We then conducted a comparative analysis of the two trees using ARACNE to evaluate the evolutionary and functional relationship between TCS and metabolism. The results showed that such integrated analysis can give new insight into the study of bacterial evolution.This study was supported by the Korean Systems Biology
Program from the Ministry of Education, Science and
Technology through the Korea Science and Engineering
Foundation (No. M10503020001-07N0302-00112), and a
Korea Research Foundation Grant funded by the Korean
Government (MOEHRD) (KRF-2007-211-D00026). Further
supports by the LG Chem Chair Professorship and Microsoft
(S.Y.L.) are appreciated
Phylogenetic analysis based on genome-scale metabolic pathway reaction content
No full textPhylogenetic classifications based on single genes such as rRNA genes do not provide a complete and accurate picture of evolution because they do not account for evolutionary leaps caused by gene transfer, duplication, deletion and functional replacement. Here, we present a whole-genome-scale phylogeny based on metabolic pathway reaction content. From the genome sequences of 42 microorganisms, we deduced the metabolic pathway reactions and used the relatedness of these contents to construct a phylogenetic tree that represents the similarity of metabolic profiles (relatedness) as well as the extent of metabolic pathway similarity (evolutionary distance). This method accounts for horizontal gene transfer and specific gene loss by comparison of whole metabolic subpathways, and allows evaluation of evolutionary relatedness and changes in metabolic pathways. Thus, a tree based on metabolic pathway content represents both the evolutionary time scale (changes in genetic content) and the evolutionary process (changes in metabolism).This work was financially supported by the
Korean Systems Biology Research Program (M10309020000-
03B5002-00000) of the Korean Ministry of Science and Technology
(MOST). Hardware for computational analysis was supported by the
IBM-SUR program
Prediction of maximum yields of metabolites and optimal pathways for their production by metabolic flux analysis
No full textThe intracellular metabolic fluxes can be calculated by metabolic flux analysis, which uses a stoichiometric model for the intracellular reactions along with mass balances around the intracellular metabolites. In this study, metabolic flux analyses were carried out to estimate flux distributions for the maximum in silico yields of various metabolites in Escherichia coli. The maximum in silico yields of acetic acid and lactic acid were identical to their theoretical yields. On the other hand, the in silico yields of succinic acid and ethanol were only 83% and 6.5% of their theoretical yields, respectively. The lower in silico yield of succinic acid was found to be due to the insufficient reducing power, but this lower yield could be increased to its theoretical yield by supplying more reducing power. The maximum theoretical yield of ethanol could be achieved, when a reaction catalyzed by pyruvate decarboxylase was added in the metabolic network. Furthermore, optimal metabolic pathways for the production of various metabolites could be proposed, based on the results of metabolic flux analyses. In the case of succinic acid production, it was found that the pyruvate carboxylation pathway should be used for its optimal production in E. coli rather than the phosphoenolpyruvate carboxylation pathway
Analysis of EHL Considering the Number of Rolling Elements and the Shaft Load in Ball and Roller Bearings
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