Researchers from the Indian Institute of Science (IISc) in Bangalore have deciphered how cells of a single-celled green alga rotate and move by sensing and responding to laser light1. The research may provide leads for designing control algorithms for artificial systems such as microrobots and micropropellers that move and respond to light.

Light has been shown to stimulate motion of microorganisms such as bacteria, fungi, algae and insects.

To better understand this process, Prerna Sharma and Sujeet Kumar Choudhary from IISc, teaming up with Aparna Baskaran from the US-based Brandeis University, exposed numerous algal cells to varying intensities of a blue laser light in a fluid-filled chamber. They then monitored the cells’ motion using a high-speed camera.

The algal cells moved in random directions in the absence of light in the chamber. When there were very few cells, the fraction of cells moving towards the light was low. The cells possibly crowded in a way that resulted in a reduction of the available light for each cell.

At a concentration of about a million cells per cubic centimetre of fluid, the fraction of cells moving towards the light rose steadily. Their swim speeds, however, decreased. Such decrease is due to a decrease in body rotation rate, enabling each cell to detect the light source more accurately.

There are already reports of robot swarms that can sense and move towards light. The physical principles underlying the algal movement towards light could be applied to develop such artificial systems, says Choudhary.


1. Choudhary, S. K. et al. Reentrant efficiency of phototaxis in Chlamydomonas reinhardtii cells. Biophys. J. 117, 1508-1513 (2019)