Thursday, November 26, 2009

Bioengineers Produce Plastics Without Using Fossil Fuels, Engineered E. Coli Does the Job

A team of pioneering South Korean scientists have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals. This groundbreaking research, which may now allow for the production of environmentally conscious plastics, is published in two papers in the journal Biotechnology and Bioengineering to mark the journal's 50th anniversary.

Polymers are molecules found in everyday life in the form of plastics and rubbers. The team, from the prestigious KAIST University and the Korean chemical company LG Chem, led by Professor Sang Yup Lee 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 , have 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".

In August 2009, the team of South Korean scientists  succeeded in engineering the bacterium E. coli to produce the industrial chemical putrescine. The research provides a renewable alternative to the production of this important chemical which is traditionally created using fossil fuels.

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. Currently putrescine is priced at over €1,600 per ton with an estimated demand of 10,000 tons per year, which is expected to grow.

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. Now the Korean-based team, led by Professor Sang Yup Lee at KAIST, have pioneered the biotechnological production of the chemical using renewable materials.

"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 product.

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."

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