Study on algae response to light has hints for robotics

An IISc graphic about how algae respond to light when the concentration of cells is more.

Dr Prerna Sharma of the Department of Physics, charts phototaxis movement at IISc.

Dr Prerna Sharma of the Department of Physics, charts phototaxis movement at IISc.

An IISc graphic about how algae respond to light when the concentration of cells is more.

A black and white 2D image of algae responding to light, taken via a microscope by IISc scientists.

A study by researchers at the Indian Institute of Science about how certain algae collectively sense and respond to light has implications for future robotics.

The study involves linking high-speed cameras to a microscope to examine a single-celled green alga called Chlamydomonas reinhardtii, suspended in various liquid medium at different light intensities.

Researchers Dr Prerna Sharma at IISc’s Department of Physics and Ph D student Sujeet Kumar Choudhary, who collaborated with Aparna Baskaran, Associate Professor at Brandeis University, observed how the single-celled organisms sends and responds to light under various cell concentration.

The study revealed that C. reinhardtii revolved constantly and positioned its eyespot (organelle) to scan water for light like a radar antenna. When it identifies a light source, the cell begins to move towards it.

While the algae’s behavior may not be new, Dr Sharma explained that the research broke new grounds with the revelation of the physical mechanism involved in the algae’s collective sense and response to light.

“This is remarkably similar to a school of fish or a flock of birds - what we call active matter, which is nothing but a collection of self-propelled entities,” added Choudhary, the first author of the study.

While researchers found the organisms’ movement was non-uniform when in small numbers –as some of them moved away from the light source—their movement towards light (called phototaxis) substantially increased when a large number of them are grouped together.

They initially put this down to herd behavior, but they were surprised to observe that a larger number of organisms in the group moved towards light because they slowed down. “The findings indicate that slower movement helps the organisms better detect light sources,” Dr Sharma said.

The physical principles derived from the study can be applied to work on micro-robot swarms, Choudhary added.