The algae that started it all

It may seem like science fiction, but with optogenetics scientists can control the behaviour of animals by simply shining a light into their brains. And this technology began… in algae! These single-celled plants are powered by the sun and contain built-in light detectors to control their behaviour. This discovery, and the isolation of the light sensitive protein that is responsible, led to the birth of the science we now call optogenetics. Tom Crawford went to see Cambridge University’s Otti Croze and Kyriacos Leptos to try to catch some of these incredible life-forms and in these circumstances in extreme conditions...

Tom - It’s about minus 10. Well it’s not but it’s freezing and we are going to be catching some algae. But the first thing we’ve got to do here is actually break the ice - that is how cold it is… We have a cup of freezing cold water with I can see a few little bits of salt and silt and things floating around in there. So hopefully we have some algae in there.

Otti - We can hope.

汤姆,所以that was fun, Otti, scooping out some water from the freezing pond but what are we actually looking for here?

Otti - We are searching for microscopic algae which are about one hundredth of a millimeter or a tenth of the average human hair, so these algae are not visible to the naked eye. But algae are an extremely diverse type of organism and some algae are actually microscopic, such as the seaweed that you might eat in your sushi.

Tom - Is there a specific algae that we’re looking for that is used in the field of optogenetics?

Otti - Yes. We’re not guaranteed to find it in this pond. But optogenetics was born from the soil microalgae Chlamydomonas reinhardtii, so that’s ideally what we would want to to find.

Tom - As Otti mentioned, we’re trying to find the algae Chlamydomonas. This is a single cell marine plant which has arms called flagella which it uses to swim towards a light source so that it can photosynthesis and make food. It does this by using a protein called channelrhodopsin which is light sensitive. This triggers the flagella to move and propel the algae towards the light. But by taking the channelrhodopsin gene from the algae and introducing it to nerve cells in the brain, scientists can use it like a switch to turn these nerve cells on or off just by shining light onto them.

Now let's head back to the nice and warm lab…

I can see some samples on the bench and there’s a bottle of what looks like clear water. But then, if you look at the righthand side, the entire inside of the container is green, almost as though the algae are concentrated in one spot. Kyriacos - what’s going on there?

Kyriacos - That’s a phenomenon that’s called phototaxis. It’s basically a behaviour of the microalgae. Algae are the photosynthetic so they harvest light to produce their biomass. They need to be able to detect the light so that they can survive.

汤姆,所以here the algae have moved to the right of the container because there’s a window on the righthand side?

Kyriacos - Yes. Phototaxis is actually the directed motion towards the light. So they need to have a sensor to detect the light and that’s called an eyespot. What’s used in optogenetics is a particular part of the eyespot, which is the one that’s actually sensing the light.

汤姆——的一部分the eyespot that Kyriacos is referring to is the protein channelrhodopsin that I mentioned earlier. Now let's see if we managed to catch anything from the frozen pond.

Okay. I’m looking down the microscope now and I can see a little dancing circle alost. What type of algae have we found?

Kyriacos - From its morphology it might be the algae euglena but you can’t be sure just looking at it. To be absolutely sure you would have to sequence it and then their regions of the DNA of algae that act as barcodes which allow you to identify the species quite uniquely.

Tom - I’m just impressed we found anything really considering the pond was frozen!