Virus gives light a dark side

It’s easy to overlook algae, at least if you’re human. For creatures at the bottom of the food web, algae are a vital source of food. On the human-scale algae are also a major consumer of carbon dioxide, and can help pull and store carbon from the atmosphere. It might seem that healthy algae are good news, but a new paper in New Phytologist by Kimberlee Thamatrakoln and colleagues takes a different tack. They refer to research that shows infected algae can improve sinking and act as a biological pump, pulling carbon down. However, viral infection isn’t something scientists look at regularly when examining algae. Thamatrakoln’s team decided to look at Emiliania huxleyi and Coccolithovirus (EhV) to see how they interact.

E. huxleyi is an interesting alga. It’s found pretty much around the world, so long as you’re in an ocean. It’s a coccolithophore, which means it’s an alga with calcium carbonate scales around it. That’s chalk, and coccolithophores are a big component of geological formations like the White Cliffs of Dover. It’s also not actually a plant. It’s a protist, an organism that has a nucleus, but doesn’t fit into the animal, fungal or plant kingdoms. But it does photosynthesise. That means it needs light, and Thamatrakoln and colleagues decided to see how that interacted with the EhV virus.

They found that whether the alga was in light or dark conditions had a significant effect on infection, with EhV having little impact in the dark. However, once light was added to the system, the virus got to work. The authors argue the lipid raft production is connected to light, and that lipid rafts are known as entry points for other pathogens, so when light hits the alga, the door is opened to the virus.

They also found that light helped EhV reproduction – at least to an extent. They say: “Our laboratory‐based data suggest EhV adsorption, and subsequent conversion and/or synthesis of nucleotides, is enhanced in the light, and that maximum viral replication occurred at mid‐range irradiance levels. At high light, viral production may be inhibited by high reactive oxygen species production… whereas at low light there may simply not be enough de novo nucleotide synthesis to support high viral production.”

They also suggest that light could directly harm the virus. The authors refer back to earlier work that argues ultraviolet breaks down viruses in the ocean, but also recent work that shows light at photosynthetic wavelengths can break down viruses.

The findings in the lab are consistent with algae and viruses found during a 2000 mile survey of the North Atlantic between the Azores and Iceland. It means the lab results could be used to start modelling the effects of viruses on phytoplankton, with those results being useful for things like carbon cycling.