by Anneli Waara

The studied algae, Chlamydomonas reinhardtii, as seen through an electron microscope.

The studied algae, Chlamydomonas reinhardtii, as seen through an electron microscope. Photograph: Dartmouth Electron Microscope Facility, Dartmouth College

That green algae can produce hydrogen under certain conditions has been known and studied for about 15 years, but low efficiency has been a problem, i.e. the amount of energy absorbed by the algae that is transformed into hydrogen.

One enzyme that has the ability to use sunlight to split water into electrons, hydrogen ions and oxygen is Photosystem II. Several studies have shown that some of the electrons from the enzyme are used to produce hydrogen gas under special conditions. But some have stated that most of the hydrogen gas gets its energy from other paths in the metabolism of the green algae. This would entail that it is not a matter of actual direct production of hydrogen from sunlight, and that green algae are no more efficient as energy crops than plants.

However, a group of researchers at Sweden’s Uppsala University, led by Senior Lecturer Fikret Mamedov and Professor Stenbjörn Styring, have just announced a discovery that changes the view on hydrogen production from green algae. The researchers studied in detail how Photosystem II works in two different strains of the green algae Chlamydomonas reinhardtii. By measuring exactly how the amount and activity of Photosystem II varies under different conditions, and thereby affects hydrogen production, they found that a considerable amount of the energy absorbed by Photosystem II goes directly into hydrogen production.

“As much as 80 per cent of the electrons that the hydrogen-producing hydrogenases need come from Photosystem II, which is much more than previously believed. This means that most of the hydrogen production is driven directly by solar energy. The discovery gives us hope that in the future it will be possible to control the green algae so that the efficiency becomes significantly higher than it is today,” says Professor Stenbjörn Styring.

The study, published in the journal PNAS, received funding from, among others, the Swedish Energy Agency, the Knut and Alice Wallenberg Foundation and the Swedish Research Council.