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Tobacco re-imagined as a future fuel source

Algal genes are introduced into tobacco cells that grow into plants. Peggy Lemaux/UC Berkeley

Tobacco doesn’t immediately conjure up ideas of fuel for cars and planes. But that’s precisely what a three-year, $4.8m project from the US Department of Energy’s ARPA-E PETRO (Plants Engineered to Replace Oil) program aims to rectify.

The tobacco plant does not naturally produce high levels of oils in its leaves, so researchers are introducing genes from blue-green and green microalgae, plants and bacteria that would allow the plant to use photosynthesis to directly convert carbon dioxide from the air into oils which could be used as fuel.

Rather than adding to the greenhouse gas problem, this approach, if successful, is a zero-sum game - it uses CO2 from the air rather than producing it. Additionally, by creating oil directly in the plant it does away with the costly processing and conversion required in other biofuel approaches used to turn biological matter into fuels.

But why tobacco? One frequent argument against biofuels is that plants grown for fuel compete with plants grown for food, with negative impacts on food security and prices. Using tobacco, which is widely grown but has never been a food crop, side-steps the food versus fuel argument. What’s more, this approach is made more attractive because tobacco is a high biomass plant, producing large amounts of leaf mass. The more biomass produced, the more oil is available. It will also allow farmers who have been growing tobacco for generations to continue that tradition - but for a different, more meaningful, purpose (and after all, tobacco markets in Europe, the US and most other regions are shrinking).

In order to improve the oil generation in tobacco, researchers at the Lawrence Berkeley National Laboratory and the University of California, Berkeley, have turned their attention to certain algae that are able to convert energy from sunlight into oil. The aim is then to introduce certain algal genes into the tobacco genome to add to existing pathways to enable plants to produce biofuels. Another aim is to improve photosynthetic efficiency that would allow tobacco to convert sunlight into energy even more efficiently, and thus lead to larger quantities of oil.

To introduce the new genetic material, the researchers use very small pieces of tobacco leaves to introduce the desired genes. A naturally occurring bacterium, Agrobacterium that can inject genetic material into plant cells, is used. The result is that the new genes become a heritable part of the tobacco plant. The small pieces of leaf tissue are then placed on a culture medium where only those cells containing the introduced genes are able to grow. From the seemingly dead leaf tissue arise leaves and roots from the engineered cells, ultimately resulting in a new plant, every cell of which will contain the new genetic material.

Additionally, colleagues at the Kentucky Tobacco Research and Development Center at the University of Kentucky are examining agricultural methods. Large-scale tobacco growing practices and harvesting infrastructure already exist and the KTRDC researchers are examining how these can be improved to generate greater amounts of biomass. Current improvements are focused on increasing the amount of biomass produced per acre of land, which would result in higher oil production.

A year and a half into the project, the researchers have demonstrated that the engineered plants produce the desired oils and have developed techologies to extract the oils using organic solvents. Current thinking is that bio-refineries could purchase the tobacco to extract its oil-rich content. The crude product could then be sold, as is, to existing oil refineries for use as gasoline, kerosene, or biodiesel, processed separately or blended with fossil crude oil for high volume production.

The challenge for this project now is to increase levels of oil to make the process economically competitive with other fuel-generating approaches. Much more research is needed before tobacco plants produce biofuels at commercial levels and will be available to growers - but preliminary results are encouraging. If successful, this approach provides a shortcut to producing fuels by direct conversion of CO2 into energy-dense liquid biofuels, using energy from the sun. The humble tobacco plant could become a future fuel-generating factory.

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