19June 2021 ESRFnews

BIOFUELS

OUT in the fields, they call it green gold: vast res-ervoirs of algae. While the sun shines through the plastic enclosures, air from outside is bubbled through, and the algae convert carbon dioxide (CO2) into hydrocarbon fuel. It is a simple reaction that transforms humanity s most shameful waste into its most pressing need. This is a fictional scenario, but also a plausible one. Over

the past few years, a group of biochemists led by Fred Beis- son at the Institute of Biosciences and Biotechnologies of Aix-Marseille a joint institute of the French Alternative Energies and Atomic Energy Commission, the French National Centre for Scientific Research and the University of Aix-Marseille have been using the ESRF to investigate an enzyme of a particular freshwater species of microalgae, Chlorella variabilis. Like other plants, C. variabilis absorbs CO2 and turns it into cellular material, such as fatty acids, via photosynthesis. But it also hosts a rare photoenzyme, which under sunlight is able to turn those fatty acids into hydrocarbons. According to Beisson and colleagues, there is a real possibility that C. variabilis or other organisms host-

The green revolution ESRF users are showing how algae can turn carbon dioxide into fuel, with potentially climate-saving results.

ing the photoenzyme could be engineered and grown in reservoir-factories to convert a greenhouse gas into usable fuel not to mention solvents, cosmetics, pharmaceuticals and other hydrocarbon products. Fatty acids differ from pure hydrocarbons only in that

their carbon chain is terminated by a pair of oxygen atoms. Industrially, removing this carboxylic head requires elec- trolysis, an expensive and energy-hungry process, and the use of corrosive reactants, such as sodium hydroxide. Sci- entists first suspected that certain microalgae are able to naturally produce hydrocarbons in the 1970s, but there were concerns that the results could have been tainted by contaminants. Four decades on, lured by the prospect of a literally green source of fuel, Beisson s group decided to find out for sure. In 2016, the researchers performed tests on several pure cultures of microalgae, and found that one of them, C. variabilis, could indeed convert fat into fuel, in the presence of sunlight. But how it worked was a mystery. The following year, the researchers used biochemistry

and proteomics techniques to identify the protein able to

Photobioreactors containing algae could be a sustainable source of hydrocarbons.