1 September 2009

Renewable way to produce industrial chemical

There is now a renewable way to produce the industrial chemical putrescine.

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 used to synthesize nylon-4,6, a widely used engineering plastic. Currently, putrescine costs over $2,294 (€1,600) per ton with an estimated demand of 10,000 tons per year.

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 and could have severe repercussions for the environment and human health. Now the South Korean-based team, led by Professor Sang Yup Lee at Korea Advanced Institute of Science and Technology, created 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,” Lee said. “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 researchers can enhance a cell’s metabolic and regulatory networks 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, came together while researchers engineered a global regulator to further increase the concentration of putrescine. The final result of this process: An engineered E. coli strain, which produced 24.2 g of putrescine per liter.

However, since researchers believed putrescine is toxic to microorganisms, the team had to study putrescine tolerance in E. coli before they could engineer it to overproduce the chemical to the levels needed for industrial production.

The results revealed 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 a surprise as it means they can engineer E. coli to overproduce putrescine to industrially competitive levels.

“The previously expected toxicity of putrescine may explain why its microbial production has been overlooked,” Lee said. “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.”

For related information, go to www.isa.org/environment.