CERTAIN marine phytoplankton move vertically in water to reach regions with sufficient illumination for photosynthesis. A research team in France has investigated similar behaviour in the algae Chlamydomonas reinhardtii. When their light-sensitive part is exposed to light, the algae can move two flagella to swim towards the light source. The researchers placed these algae in water flowing through a pipe and used a fast-imaging technique to observe them as they moved in response to the illumination. The combination of the flow drag and the attraction due to light caused the algae to gather around the central axis of the pipe.
The effect, say the researchers, could be exploited for biohydrogen production—where algae expel hydrogen gas during photosynthesis—to prevent the organisms from clinging to walls and facilitate the gas separation process.
