Engineering plants to make plastics
Modern society's reliance on fossil fuel extends past its use as an energy source with by-products used in everything from plastics to lubricants and fertilizers. Seeking alternatives that are cleaner to produce and renewable is important for the continuation of life as we know it. This is why researchers the the U.S Department of Energy (DOE) are are engineering plants to produce chemicals needed for plastics that have traditionally come from fossil fuels.
The key to the research is getting plants to produce higher yields of particular fatty acids (FAs) in their seeds. Of interest is the group of omega-7 FAs which are used in the production of plastics. Brookhaven National Laboratory and DOE biochemist John Shanklin told Gizmag that over half a million tons of these omega-7 FAs are consumed globally each year. The discovery of the genes that code for the enzymes responsible for producing these FAs encouraged researchers to explore ways of expressing these genes.
While initial results were poor using the common laboratory plant Arabidopsis, Shanklin persisted and was able to increase FA production from below two percent to 14 percent after introducing a laboratory engineered enzyme that worked faster and with greater specificity than natural enzymes. This was still an unacceptable industrial scale production so he tried again. Additional modifications to the plant’s metabolic pathways were made, down regulating genes that compete for the introduced enzyme’s FA substrate and recapturing enzymes missed in the oil-accumulation process to be recycled and converted to the desired FA.
Having tested various traits individually, the team then combined the most promising traits into a single new plant. The results were impressive with an accumulation of the desired omega-7 FA at levels of around 70 percent in the best engineered plants. While additional technology is needed to efficiently convert the plant FAs into the chemical building blocks for plastic production the research shows that high levels of the appropriate feedstock can be made in plants.
“The raw materials for most precursors currently come from petroleum or coal derived synthetic gas," said Shanklin. "Our new way of providing a feedstock sourced from fatty acids in plant seeds would be renewable and sustainable indefinitely. This proof of principle experiment is a successful demonstration of a general strategy for metabolically engineering the sustainable production of omega-7 fatty acids as an industrial feedstock source from plants.”
Shankin told Gizmag that while these FAs could only be used to produce low density polyethylene, the principles could be applied to the production of other plastic products.
“Different plastics are made from different feedstocks. We could defiantly apply the same principles to designing plants to produce a variety of other feedstocks. Other unusual fatty acids include unusual monoenes such as petroselenic acid, 18:1delta-6 from coriander seed, or hydroxy fatty acids such as ricinoleic acid from castor bean, both of which have potential uses as polymer feedstocks and the hydroxy fatty acid as a lubricant.”