French researchers show that the alga Chlorella variabilis can efficiently convert medium fatty acids into petrol-like hydrocarbons. However, commercial application is still a long way off.

Searching for carbon-neutral alternatives to fossil fuels, scientists discovered the enzyme CvFAP in 2017. It is a fatty acid photodecarboxylase (FAP), an enzyme that converts fatty acids into hydrocarbons under the influence of light, and is found in Chlorella variabilis (Cv), a microalgae. The algae is particularly good at the production of long hydrocarbons (C16-C18). Now, French researchers have shown that CvFAP has a special talent for converting medium-length fatty acids (C8-C10) into medium-length hydrocarbons. This is useful. It is precisely these chain lengths that yield biofuels similar to petrol. They published their results on 31 March in Science Advances.

Chlorella variabilis FAP can convert n-octanoic acid four times faster than n-hexadecanoic acid, which was previously the best performing substrate, the researchers write. In vivo, the CvF AP-based production rate is more than 10 times higher for n-heptanoic acid than for n-pentadecane. Spectroscopy and molecular modelling show that this high activity on n-octanoic acid is due to an autocatalytic effect of the resulting n-heptane.

’It is a solid piece of research and an addition to our knowledge of photocarboxylase. For our understanding of the enzyme, it is certainly relevant and mechanistically interesting,’ says Joost Teixeira de Mattos, emeritus professor of microbiology and co-founder of Photanol, who was not involved in the research. ‘But the step to large-scale application for fuel production is far too big. There is no testing anywhere on how stable the enzyme is, how long it retains its activity or how it behaves in bulk solutions. Nor do they mention anything about large-scale production of the enzyme or about expression and activity in vivo. It is not relevant for commercial or large-scale production of green fuel.’

Samire et al, Sci. Adv. (2023) (Open Access)