research
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The thermal fluctuation and elasticity of cell membranes, lipid vesicles, interacting with pore-forming peptides were reported by a research team at KAIST.
A research team from KAIST, consisted of Sung-Min Choi, Professor of Nuclear and Quantum Engineering Department, and Ji-Hwan Lee, a doctoral student in the Department, published a paper on the “thermal fluctuation and elasticity of lipid vesicles interacting with pore-forming peptides.” The paper was carried by Physical Review Letters, an internationally renowned peer-review journal on physics on July 16, 2010.
Cell membranes, which consist of lipid bilayers, play important roles in cells as barriers to maintain concentrations and matrices to host membrane proteins. During cellular processes such as cell fission and fusion, the cell membranes undergo various morphological changes governed by the interplay between protein and lipid membranes. There have been many theoretical and experimental approaches to understand cellular processes driven by protein-lipid membrane interactions. However, it is not fully established how the membrane elastic properties, which play an important role in membrane deformation, are affected by the protein-membrane interactions.
Antimicrobial peptides are one of the most common examples of proteins that modify membrane morphology. While the pore-forming mechanisms of antimicrobial peptides in lipid bilayers have been widely investigated, there have been only a few attempts to understand the mechanisms in terms of membrane elastic properties. In particular, the effects of pore formation on the membrane fluctuation and elastic properties, which provide key information to understand the mechanism of antimicrobial peptide activity, have not been reported yet. The research team reports the thermal fluctuation and elasticity of lipid vesicles interacting with pore-forming peptides, which were measured by neutron spin-echo spectroscopy.
The results of this study are expected to pay an important role in understanding the elastic behavior and morphological changes of cell membranes induced by protein-membrane interactions, and may provide new insights for developing new theoretical models for membrane fluctuations which include the membrane mediated interaction between protein patches.
(a) (b)
Figure
(a) Schematics for bound melittin and pores in lipid bilayers
(b) P NMR signal ratio (with/without Mn2+) of DOPC LUV-melittin vs P/L at 30˚C. The dashed line is a guide for eyes.
2010.07.23 View 11288 -
Professor Eun-Seong Kim and his research staff observed the phenomena of hysteresis and relaxation dynamics from supersolid Helium
Professor Eun-Seong Kim and his research staff observed the phenomena of hysteresis and relaxation dynamics from supersolid Helium.
Their research paper was published in Nature Physics for the issue of April 2010.
If we take Helium 4 and cool it down at temperatures below 2.176 Kelivin, liquid helium 4 undergoes a phase transition and becomes superfluid with a zero viscosity. The superfluidity was observed in solid helium through an experiment performed by researchers of Pennsylvania State University in 2004. One of the researchers then was Professor Eun-Seong Kim in the Department of Physics, KAIST.
Professor Kim and his research staff, Hyung-Soon Choi, Ph.D., recently published their research results in Nature Physics (April 2010), a highly esteemed journal in the field, on the phenomena of hysteresis and relaxation dynamics observed in supersolid Helium.
For the paper, please download the attached .pdf file.
Nature Physics link: http://www.nature.com
2010.04.13 View 12006 -
New drug targeting method for microbial pathogens developed using in silico cell
A ripple effect is expected on the new antibacterial discovery using “in silico” cells
Featured as a journal cover paper of Molecular BioSystems
A research team of Distinguished Professor Sang Yup Lee at KAIST recently constructed an in silico cell of a microbial pathogen that is resistant to antibiotics and developed a new drug targeting method that could effectively disrupt the pathogen"s growth using the in silico cell.
Hyun Uk Kim, a graduate research assistant at the Department of Chemical and Biomolecular Engineering, KAIST, conducted this study as a part of his thesis research, and the study was featured as a journal cover paper in the February issue of Molecular BioSystems this year, published by The Royal Society of Chemistry based in Europe.
It was relatively easy to treat infectious microbes using antibiotics in the past. However, the overdose of antibiotics has caused pathogens to increase their resistance to various antibiotics, and it has become more difficult to cure infectious diseases these days.
A representative microbial pathogen is Acinetobacter baumannaii. Originally isolated from soils and water, this microorganism did not have resistance to antibiotics, and hence it was easy to eradicate them if infected. However, within a decade, this miroorganism has transformed into a dreadful super-bacterium resistant to antibiotics and caused many casualties among the U.S. and French soldiers who were injured from the recent Iraqi war and infected with Acinetobacter baumannaii.
Professor Lee’s group constructed an in silico cell of this A. baumannii by computationally collecting, integrating, and analyzing the biological information of the bacterium, scattered over various databases and literatures, in order to study this organism"s genomic features and system-wide metabolic characteristics. Furthermore, they employed this in silico cell for integrative approaches, including several network analysis and analysis of essential reactions and metabolites, to predict drug targets that effectively disrupt the pathogen"s growth. Final drug targets are the ones that selectively kill pathogens without harming human body.
Here, essential reactions refer to enzymatic reactions required for normal metabolic functioning in organisms, while essential metabolites indicate chemical compounds required in the metabolism for proper functioning, and their removal brings about the effect of simultaneously disrupting their associated enzymes that interact with them.
This study attempted to predict highly reliable drug targets by systematically scanning biological components, including metabolic genes, enzymatic reactions, that constitute an in silico cell in a short period of time.
This research achievement is highly regarded as it, for the first time, systematically scanned essential metabolites for the effective drug targets using the concept of systems biology, and paved the way for a new antibacterial discovery. This study is also expected to contribute to elucidating the infectious mechanism caused by pathogens.
"Although tons of genomic information is poured in at this moment, application research that efficiently converts this preliminary information into actually useful information is still lagged behind. In this regard, this study is meaningful in that medically useful information is generated from the genomic information of Acinetobacter baumannii," says Professor Lee. "In particular, development of this organism"s in silico cell allows generation of new knowledge regarding essential genes and enzymatic reactions under specific conditions," he added.
This study was supported by the Korean Systems Biology Project of the Ministry of Education, Science and Technology, and the patent for the development of in silico cells of microbial pathogens and drug targeting methods has been filed.
[Picture 1 Cells in silico]
[Picture 2 A process of generating drug targets without harming human body while effectively disrupting the growth of a pathogen, after predicting metabolites from in silico cells]
2010.04.05 View 14717 -
Photonic crystals allow the fabrication of miniaturized spectrometers
By Courtesy of Nanowerk
Photonic crystals allow the fabrication of miniaturized spectrometers
(Nanowerk Spotlight) Spectrometers are used in materials analysis by measuring the absorption of light by a surface or chemical substance. These instruments measure properties of light over a specific portion of the electromagnetic spectrum. In conventional spectrometers, a diffraction grating splits the light source into several beams with different propagation directions according to the wavelength of the light. Thus, to achieve sufficient spatial separation for intensity measurements at a small slit, a long light path – i.e., a large instrument – is required.
However, for lab-on-a-chip or microTAS (total analysis system) applications, the spectrometer must be integrated into a sub-centimeter scale device to produce a stand-alone platform. To achieve this, researchers at the Korea Advanced Institute of Science and Technology (KAIST) propose a new paradigm in which the spectrometer is based on an array of photonic crystals with different bandgaps.
"Because photonic crystals refelct light of different wavelengths selectively depending on their bandgaps, we can generate reflected light spanning the entire wavelength range for analysis at different spatial positions using patterned photonic crystals," Seung-Man Yang, Director of the National Creative Research Initiative Center for Intergrated Optofluidic Systems and Professor of the Department of Chemical & Biomolecular Engineering at KAIST, tells Nanowerk. "Therefore, when the light source impinges on the patterned photonic crytals, we can construct the spectrum using the reflection intensity profile from the constituent photonic crystals."
Photonic crystals – also known as photonic band gap material – are similar to semiconductors, only that the electrons are replaced by photons (i.e. light). By creating periodic structures out of materials with contrast in their dielectric constants, it becomes possible to guide the flow of light through the photonic crystals in a way similar to how electrons are directed through doped regions of semiconductors. The photonic band gap (that forbids propagation of a certain frequency range of light) gives rise to distinct optical phenomena and enables one to control light with amazing facility and produce effects that are impossible with conventional optics.
To demonstrate this new concept based on patterned photonic crystals, Yang and his group used non-close-packed colloidal crystals of silica particles dispersed in photocurable resin. Due to the repulsive interparticle potential, monodisperse silica particles spontaneously crystallize into non-close-packed face-centered cubic (fcc) structures at volume fractions above 0.1. Therefore, the particle volume fraction determines both the lattice constant and the bandgap position.
a) Optical image of an ETPTA film containing porous photonic crystal stripe patterns with 20 different bandgaps. b) Reflectance spectra from the 20 strips. c) Optical microscope image of the middle region with the parallel stripe pattern (denoted as white-dotted box in a). d) Cross-sectional SEM images of first, sixth, eleventh and seventeenth strips. The scale bars in a, c and d are 1 cm, 2mm and 2 µm, respectively. (reprinted with permission from Wiley-VCH Verlag)
Reporting their findings in a recent issue of Advanced Materials ("Integration of Colloidal Photonic Crystals toward Miniaturized Spectrometers"), the KAIST team has demonstrated the integration of colloidal photonic crystals with 20 different bandgaps into freestanding films (prepared by soft lithography), and their application as a spectrometer.
Yang explains that the team was able to precisely control the photonic bandgap by varying the particle size and volume fration.
"The prepared colloidal composite structures showed high physical rigidity and chemical resistivity" he says. "The composite structure is suitable for spectroscopic use due to the small full widths at half maximum (FWHMs) of the reflectance spectra, which mean that there is little overlap of the reflectance spectra of neighboring photonic crystal strips."
"On the other hand" says Yang, "porous photonic crystals showed large FWHMs and high reflectivities, which should prove useful in many practical photonic applications that require high optical performance and physical rigidity as well as simple and inexpensive preparation."
In addition to fabricating miniaturized spectrometers, which can for instance be integrated into small lab-on-a-chip devices, these integrated photonic crystals can be potentially used for tunable band reflection mirrors, optical switches, and tunable lasing cavities. Moreover, patterned photonic crystals with RGB colors are well-suited for use in reflection-mode microdisplay devices.
Yang points out that, although the spectrometric resolution can be reduced by employing the smaller bandgap interval and photonic bandwidth, there is a limitation. "Now, we are studying photonic crystals with continuous modulation of bandgap position. We expect that the photonic crystals can reduce the resolution to 0.01 nm."
By Michael Berger. Copyright 2010 Nanowerk
2010.03.17 View 13134
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A Breakthrough for Cardiac Monitoring: Portable Smart Patch Makes It Possible for Real-time Observation of Heart Movement
Newly invented device makes the monitoring easier and convenient.
Professor Hoi-Jun Yoo of KAIST, Department of Electrical Engineering, said that his research team has invented a smart patch for cardiac monitoring, the first of its kind in the world. Adhesive and can be applied directly to chest in human body, the patch is embedded with a built-in high performance semiconductor integrated circuit (IC), called Healthcare IC, and with twenty five electrodes formed on the patch’s surface.
The 25-electrodes, with a capability of creating various configurations, can detect cardiac contractions and relaxations and collect electrocardiogram (ECG) signals. The Healthcare IC monitors ECG signals and sends the information to a portable data terminal like mobile phones, making it possible for a convenient, easy check up on cardiac observations.
The key technologies used for the patch are the Healthcare IC that measures cardiovascular impedance and ECG signals, and the electronic circuit board made of four layers of fabric, between which electrodes, wireless antenna, circuit board, and flexible battery are installed. With the P-FCB (Planar Fashionable Circuit Board) technology, the research team explained, electrodes and a circuit board are directly stacked into the fabric. Additionally, the Healthcare IC (size: 5mm x 5mm), which has components of electrode control unit, ECG and cardiovascular resistance detection unit, data compression unit, Static Random Access Memory (SRAM), and wireless transmitter receiver, is attached on the fabric. The Healthcare IC is operated by an ultra-low electrical power.
Like a medicated patch commonly used to relieve arthritis pains, the surface of smart patch is adhesive so that people can carry it around without much hassle. A finished product will be 15cm x 15 cm in size and 1mm high in thickness. The Healthcare IC can measure cardiovascular impedance variances with less than 0.81% distortion in 16 different configurations through differential current injectors and reconfigurable high sensitivity detection circuitry.
“The patch will be ideal for patients who suffer a chronic heart disease and need to receive a continuous care for their condition. Once commercialized, the patch will allow the patients to conduct a self-diagnosis at anytime and anywhere,” said Yan Long, a member of the research team.
There has been a continuously growing demand worldwide since 2000 for the development of technology that provides a suitable healthcare management to patients with a chronic heart disease (e.g., cardiovascular problems), but most of the technology developed today are only limited to monitoring electrical signals of heart activity. Cardiovascular monitors, commonly used at many of healthcare places nowadays, are too bulky to use and give uncomfortable feelings to patients when applied. Besides, the current monitors are connected to an electrical line for power supply, and they are unable to have a low power communication with an outdoor communication gadget, thus unavailable for wide use.
Professor Yoo gave his presentation on this new invention at an international conference, International Solid-State Circuits Conference, held on February 8-10 in San Francisco. The subject of his presentation was “A 3.9mW 25-electorde Reconfigurable Thoracic Impedance/ECG SoC with Body-Channel Transponder.”
(Picture 1) Structure of Smart Patch
(Picture 2) Smart patch when applied onto human body
(Picture 3) Data received from smart patch
(Picture 4) Healthcare IC
2010.02.17 View 13816
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Indoor Localization System for Mobile Devices Developed by KAIST Research Team
The technology will be available to smart phone users around the world through Goole Apps Store.
The wireless fidelity (WiFi)-based indoor localization can be installed on smart phones for commercialization, a technology developed by a research team at KAIST. The KAIST research team, led by Professor Dong-Soo Han, Department of Computer Science and Engineering, explained that the technology offers smart phone users, e.g., Google’s Android phone and Apple’ iPhone, a unique way to recognize their location through WiFi Open Radio Map. WiFi Open Radio Map is built with WiFi Location Fingerprint that contains wireless local area network (LAN)’s signal strength and wireless access points (AP) number, and with location information.
Through using the Map, WiFi-based indoor localization recognizes the location of smart phones and sends the location information to the phones. Since the technology uses WiFi signal information only to recognize the whereabouts of phones, it can be widely used in the future, without installing extra machines and equipment for detection, for a complicated, large indoor environment, where the Global Positioning System (GPS) is not available.
Currently, Professor Han has established WiFi Open Radio Map inside and outside of a few buildings at KAIST and developed several location based application services to perform a beta testing. He plans to open and distribute the technology to smart phone users through Google and Apple Apps Store in early 2010. Collaborations with major smart phone makers such as SK Telecom, Korea Telecom, and Samsung as well as outdoor/indoor localization manufactures and suppliers will also be sought, according to Professor Han.
Professor Han is invited to an international conference, Eighth Annual IEEE International Conference on Pervasive Computing and Communications, slated for early April 2010, in recognition of his work. At the conference, he will give a presentation on WiFi based indoor localization technology and conduct its demo version.
2010.02.10 View 11027
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KAIST Research Team Identified Promising New Source to Obtain Stem Cells
KAIST Research Team Identified Promising New Source to Obtain Stem Cells
A research team at KAIST led by Professor Gou-Young Koh, M.D. and Ph.D., of the Department of Biological Sciences, has found evidence that fat tissue, known as adipose tissue, may be a promising new source of valuable and easy-to-obtain regenerative cells called hematopoietic stem and progenitor cells (HSPCs).
HSPCs are adult stem cells that have the ability to generate and develop into many different kinds of cells. They are now used to repair damaged tissues and are being studied for their potential to treat a vast array of chronic and degenerative conditions such as leukemia. Mostly found in bone marrow but with a limited quantity, HSPCs are hard to cultivate in vitro, thus becoming an obstacle to use them for research and therapeutic purposes.
Within the adipose tissue is a special cell population known as the stromal vascular fraction (SVF), which share similar properties to those in the bone marrow. Cells in the bone marrow and SVF have the ability to differentiate into several cell types. In addition, both adipose and bone marrow offer similar environments for optimal stem cell growth and reproduction.
Given the fact that adipose and bone marrow tissues share similar properties, Dr. Koh and his team conducted a research, injecting granulocyte colony-stimulating factor (G-CSF), a growth hormone used to encourage the development of stem cells, into an adipose tissue of a mouse whose bone marrow is damaged. As a result, the team has found that the SVF derived from adipose tissue contains functional HSPCs capable of generating hematopoietic (blood-forming) cells to repair the damaged bone morrow.
The Ministry of Education, Science and Technology nominated the KAIST research as one of its sponsoring 21st Century Frontier R&D Programs. Director Dong-Wook Kim of Stem Cell Research Center (SCRS) that oversees the KAIST team expressed a possibility to use the adipose tissue as an alternative source to obtain stem cells for regeneration medicine.
Dr. Koh also said, “It’s been a well known method to extract HSPCs from the bone morrow or blood, but it’s the first time to identify adipose tissue, before considered useless, as a new possible supplier for functional and transplantable HSPCs.”
The study results have received an important recognition from the academia—the American Society of Hematology published the research as a main article in its official journal, Blood, for the February 4th, 2010 issue, which is the most citied peer-reviewed publication in the field.
2010.02.05 View 11702
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Prof. Lee"s Team Succeeds in Producing Plastics Without Use of Fossil Fuels
A team of scientists led by Prof. Sang-Yup Lee of the Department of Biological Sciences at KAIST have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals, the university authorities said on Tuesday (Nov. 24).
This groundbreaking research, which may now allow for the production of environmentally conscious plastics, has been published in two papers in the journal Biotechnology and Bioengineering.
Polymers are molecules found in everyday life in the form of plastics and rubbers. The team consisted of scientists from KAIST and Korean chemical company LG Chem focused their research on polylactic acid (PLA), a bio-based polymer which holds the key to producing plastics through natural and renewable resources.
"The polyesters and other polymers we use everyday are mostly derived from fossil oils made through the refinery or chemical process," said Lee. "The idea of producing polymers from renewable biomass has attracted much attention due to the increasing concerns of environmental problems and the limited nature of fossil resources. PLA is considered a good alternative to petroleum based plastics as it is both biodegradable and has a low toxicity to humans."
Until now PLA has been produced in a two-step fermentation and chemical process of polymerization, which is both complex and expensive. Now, through the use of a metabolically engineered strain of E.coli, the team has developed a one-stage process which produces polylactic acid and its copolymers through direct fermentation. This makes the renewable production of PLA and lactate-containing copolymers cheaper and more commercially viable.
"By developing a strategy which combines metabolic engineering and enzyme engineering, we"ve developed an efficient bio-based one-step production process for PLA and its copolymers," said Lee. "This means that a developed E. coli strain is now capable of efficiently producing unnatural polymers, through a one-step fermentation process,"
This combined approach of systems-level metabolic engineering and enzyme engineering now allows for the production of polymer and polyester based products through direct microbial fermentation of renewable resources.
"Global warming and other environmental problems are urging us to develop sustainable processes based on renewable resources," concluded Lee. "This new strategy should be generally useful for developing other engineered organisms capable of producing various unnatural polymers by direct fermentation from renewable resources".
2009.11.30 View 13944 -
Prof. Woo's Team Discovers Eco-Friendly Solid-Oxide Fuel Cell System
A KAIST research team led by Prof. Seong-Ihl Woo of the Department of Chemical & Biomolecular Engineering has found a method to use glycerol, a byproduct from the production of biodiesel, as fuel for solid oxide fuel cells (SOFC), university authorities said on Tuesday (Oct. 27).
The research finding shows that glycerol can be an environmentally sustainable fuel when it is used for operating SOFCs with internal reforming, instead of hydrogen and methane. The finding was published in the Oct. 14, 2009 online edition of ChemSusChem, a sister journal of Angewandte Chemie, the world"s leading chemistry journal.
Biodiesel is an attractive alternative energy source because of its low sulfur content and demand is growing worldwide as oil price soars. Bio-derived glycerol will not contribute to the greenhouse effect and has the potential to contribute to reducing global warming.
Currently, glycereol is used as a raw material in the cosmetic, pharmacy, food, and tobacco industries. However, its supply exceeds its demand as the volume of biodiesel production increases. The production of 1 ton of biodiesel produces 0.1 ton of glycerol. Many researchers have investigated various routes for the consumption of surplus glycerol.
The research is expected to contribute to sustainable growth by reducing the emissions of carbon dioxide and reusing generated carbon dioxide for the production of biomass. The new method enables manufacturers to use glycerol as a fuel for operating SOFC.
2009.10.28 View 12355 -
Prof. Ryoo's Team Discovers Breakthrough Method to Create New Zeolite
A group of scientists led by Prof. Ryong Ryoo of the Department of Chemistry, KAIST, has found a method to direct the growth of zeolite, a crystalline substance that is frequently used as catalyst in the chemical and petrochemical industries, the university authorities said on Thursday (Sept. 10).
Ryoo"s research team successfully created ultrathin nano-sheets, only two nano-meters thick, that are efficiently used as long-life catalysts for hydrocarbon cracking and other petrochemical applications. The breakthrough finding, which is credited with taking acidic zeolite catalysts to the limit in terms of thickness, was published in the latest edition of the peer-review journal, "Nature."
A team from the Polytechnic Univeristy of Valencia, Spain, also contributed to the research.
Zeolites are already widely used in the petrochemical industry, but making the catalysts very thin means that reactant molecules can easily diffuse into the zeolite structure and product molecules can get out quickly. This improves the efficiency of the catalyst and reduces unwanted side reactions that can produce polymeric hydrocarbon "coke" that clogs the zeolite pores and eventually kills the catalytic activity, Prof. Yoo said.
To make the thin sheets, Ryoo and his team used a surfactant as a template to direct the growth of the zeolite structure. The surfactant molecule has a polar "head" group - with two quaternary ammonium groups around which the aluminosilicate zeolite crystal grows - and a long hydrocarbon "tail," which prevents the sheets from aggregating together into larger, three dimensional crystals. When the surfactant is removed, these flakes pile up randomly with gaps in between which further aids diffusion to the catalyst sites.
"Zeolite could be used as a catalyst to convert heavy oil into gasoline. Our new zeolite could provide even more possibilities, such as being used as catalysts for transforming methanol into gasline," Ryoo said.
Prof. Ryoo, a Distinguished Professor of KAIST, has won a variety of academic awards, which included the Top Scientist Award given by the Korean government in 2005 and the 2001 KOSEF Science and Technology Award for his work on the synthesis and crystal structure of mezzoporous silica.
Ryoo obtained his bachelor"s degree from Seoul National University in 1977, master"s from KAIST in 1979, and doctorate from Stanford University in 1985.
In 2006, Ryoo and his research team announced the discovery of a form of zeolite that can catalyze petrochemical reactions much more effectively than previous zeolites. Because of the potential of this to streamline the gasoline refining process, it was greeted as a "magical substance" by the South Korean press.
2009.09.11 View 11820 -
Scaling Laws between Population and Facility Densities Found
A research team led by Prof. Ha-Woong Jeong of the Department of Physics, KAIST, has found a positive correlation between facilities and population densities, university authorities said on Tuesday (Sept. 2). The research was conducted in the cooperation with a research team of Prof. Beom-Jun Kim at Sungkyunkwan University.
The researchers investigated the ideal relation between the population and the facilities within the framework of an economic mechanism governing microdynamics.
In previous studies based on the global optimization of facility positions in minimizing the overall travel distance between people and facilities, the relation between population and facilities should follow a simple law. The new empirical analysis, however, determined that the law is not a fixed value but spreads in a broad range depending on facility types.
To explain this discrepancy, the researchers proposed a model based on economic mechanism that mimics the competitive balance between the profit of the facilities and the social opportunity cost for population.
The results were published in the Proceedings of the National Academy of Sciences of the United States on Aug. 25.
2009.09.04 View 12013
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Prof. Lee"s Team Pioneers Biotechnological Production of Chemical Using Renewable Materials
A research team led by Prof. Sang-Yup Lee of the Bio and Brain Engineering Department at KAIST has succeeded in engineering the bacterium E. coli to produce the industrial chemical putrescine, university authorities said on Monday (Aug. 31).
Putrescine, a four carbon chain diamine, is an important platform chemical with a wide range of applications for the pharmaceutical, agrochemical and chemical industries. It is currently used to synthesize nylon-4,6, a widely used engineering plastic.
The research result, published in the Biotechnology and Bioengineering journal, proviDrdes a renewable alternative to the traditional process using fossil fuels.
Currently the production of putrescine on an industrial scale relies on chemical synthesis, which requires non-renewable petrochemicals and expensive catalyst systems. This process is highly toxic and flammable with potentially severe repercussions for both the environment and human health.
"For the first time we have developed a metabolically engineered E. coli strain that efficiently produces putrescine," said Professor Lee. "The development of a bio-refinery for chemicals and materials is very important in a world where dependency on fossil fuels is an increasing concern."
The team developed a strain of E.coli capable of producing putrescine through metabolic engineering. This is where a cell"s metabolic and regulatory networks are enhanced in order to increase production of a needed material.
First the team weakened or deleted competing metabolic pathways within the E. coli strain before deleting pathways which cause putrescine degradation. They also amplified the crucial enzyme Spec C, which converts the chemical ornithine into putrescine. Finally the putrescine exporter, which allows excretion of intracellularly made putrescine, was engineered while a global regulator was engineered to further increase the concentration of putrescine. The final result of this process was an engineered E.coli strain which produced 24.2 g of putrescine per litre.
However, as it was believed that putrescine is toxic to microorganisms the team had to study putrescine tolerance in E.coli before it could be engineered to overproduce the chemical to the levels needed for industrial production.
The results revealed that E. coli can tolerate at least 0.5 M of putrescine, which is tenfold higher than the usual concentration in the cell. This level of tolerance was an important surprise as it means that E. coli can be engineered to overproduce putrescine to industrially competitive levels.
"The previously expected toxicity of putrescine may explain why its microbial production has been overlooked," said Lee. "Now a metabolically engineered E. coli strain has been developed which is capable of efficiently producing putrescine using renewable methods to an industrial level. This metabolic engineering framework should be useful for developing metabolically engineered microorganisms for the efficient production of other chemicals from renewable resources," he added.
2009.09.01 View 12994