Optogenetics (from Greek word for “ visible”) is a biological technique that in which light is used to control neurons that have been genetically modified to express light-sensitive ion channels (pore-forming membrane proteins that allow ions to pass across cell membranes). 

Thus, optogenetics is a neuromodulation method that acts directly upon nerves, and changes nerve activity by delivering electrical or pharmaceutical agents directly to a target area to control the activities of individual neurons in living tissue. 

A decade ago, optogenetics was chosen as the “Method of the Year” across all fields of science and engineering by the interdisciplinary research journal Nature Methods and was highlighted in the article on “Breakthroughs of the Decade” in the academic research journal Science. Optogenetics has caused a revolution in neuroscience research and today is considered to be the best technique for activating specific cells to examine their impact on the functioning of the organism.

Researchers at the biology faculty of the Technion-Israel Institute of Technology in Haifa have for the first time discovered unique photoreceptors in giant viruses that live in the sea and the algae they infect. The study, just published in Current Biology under the title “Lateral Gene Transfer of Anion-Conducting Channelrhodopsins between Green Algae and Giant Viruses,” was performed by lead researcher Prof. Oded Béjà and postdoctoral researcher Dr. Andrey Rozenberg.

Béjà’s research team studies microbial rhodopsins – proteins that help one-celled organisms harvest light energy (in a process that differs from photosynthesis) and also detect light in a way remotely similar to animal vision. This study focused on the family of the light-activated ion channels called channelrhodopsins (ChRs), microbial rhodopsins that directly translate absorbed light into ion fluxes across cellular membranes. 

These proteins, which naturally originate in unicellular algae, are used in neuroscience for precise manipulation, stimulation and inhibition of neurons and other excitable cells, through the use of light. 

Channelrhodopsins, which were first discovered as green algal proteins localized to the so-called eyespots, help the proteins find optimal light conditions by driving their phototaxis. Different kinds of channelrhodopsins have been discovered in the recent years in other unicellular algae and also non-photosynthetic single-cell organisms.

The Technion’s research team, which performed a metagenomic analysis of seawater, has now found that viruses that infect algae contain genes coding for channelrhodopsins. The search for related proteins brought about the discovery of a whole new family of channelrhodopsins that originated in “primitive” green algae and anion-conducting activity that originated in algae. Through electrophysiological experiments, they demonstrated that the channelrhodopsins from the viruses and the algae function as anion-conducting light-dependent channels.

“Our quest led us to the conclusion that the origin of these channelrhodopsins is not in the virus but in the algae that they infect. We estimate that at some point in the evolutionary process, a giant alga-infecting virus “stole” a channelrhodopsin gene for its own benefit,” said Béjà . “We hypothesize that the viruses can manipulate the host’s swimming behavior, thus controlling its light responses and directing it to locations where irradiation conditions are favorable for the virus.”

The study is based on data collected in Tara Oceans, a global oceanic research expedition undertaken to collect samples for mapping marine biodiversity, which traveled on board the vessel Tara.The research project was carried out in collaboration with Prof. Peter Hegemann of Humboldt University of Berlin, Germany, and his team.