Researchers from the Technical University of Denmark found a way to regulate carbon emissions from plants and turn emissions into useful and ecofriendly products.

The Blue Mountains in Australia are named after the blue haze that can be seen on hot days over the forest. This haze is caused by isoprenoids that are emitted by these forests in large quantities. Isoprenoids can, when reacting with pollutants in the atmosphere, increase greenhouse gas formation. Source: DAVID ILIFF / CC BY-SA 3.0

Most plants emit volatile gases into the atmosphere. Plant isoprenoid emissions contribute to the hydrocarbon released into the atmosphere. Once in the atmosphere, isoprenoids can turn into greenhouse emissions, causing harm to the climate. It is estimated that short-chain isoprenoids account for over 80% of all volatile organic compounds emitted from all living organisms, up to 650 million tons of carbon a year.

Crops that have high isoprene emissions include palm oil trees, spruce and aspen trees. The team says that farmers can use this knowledge to optimize their farms by planting fewer high emitting plants and more zero emissions plants.

Researchers admit that they are unsure if all plant emissions have a negative effect, and more research is needed. But it is clear that the harmful effects of isoprenoid emissions happen when the emissions react with common air pollutants. Large farms or plantations with high emissions are troublesome for climate change.

The team found a new regulatory plant-based mechanism when they engineered E. coli to produce isoprenoids to replace fossil fuel chemicals. When E. coli is engineered with plant genes for an HDR enzyme, the combination produces two chemicals in different ratios and influences how much isoprene is produced. This is useful for the future of biotech.

Isoprenes have many uses, like turning into rubber. Goodyear has already produced car tires from bio produced isoprene. This could be promising for the production of nonoterpene isoprenoids to create eco-friendly jet fuel.

Typically, to create isoprenoids, researchers use a pathway from yeast. This achieves yields higher than with E. coli pathways. But a new pathway used by E. coli and plants has a higher theoretic yield. This means that more isoprenoids could be made from the same amount of sugar in E. coli than yeast. The team says that using E. coli for isoprenoid production makes more commercial sense than using yeast.

The team compared eight plant HDR genes and one cyanobacterial HDR gene in E. coli. The best results were found when using genes from a peach, poplar and castor bean. For this test the team only produced two milligrams of isoprene per liter of cell broth. With more engineering and fermentation optimization, this yield could improve and overall isoprene production in E. coli would be strengthened. Choosing the correct enzyme made a huge difference in production.

This study was published in eLife.