You wanted to know: What's the virus infecting the phytoplankton? (Part Two)


Yesterday we learned about how normal viruses work. Today, we're finally getting to how this particular Ehux virus does it's thing.

What method of predation does the virus use on Emiliania huxleyi? Jim Wallstrum Spokane from Washington

So we're back to Ehux. Just like other viruses and hosts, Ehux and Ehux-86 are locked in an evolutionary arms race. Each time one evolves a new attack mechanism, the other evolves a new defense. And so on.

To look at some examples, we should first turn to Alice in Wonderland. Seriously, stick with me here. In "Through the Looking Glass," a sequel to Alice in Wonderland, there's a scene where Alice and the Red Queen are running, but they're not going anywhere. No matter how fast they run, they seem to stay in the same place.

"Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else — if you run very fast for a long time, as we've been doing."

"A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"

This idea -- that you have to keep running just to stay in the same place -- was adopted by a biologist named Leigh Van Valen in 1973. He said that when a host and an enemy (whether that's a virus, a bacteria, a predator, or whatever else) are locked in an arms race, the host has to run and run and run to keep from being overtaken by its enemy. In our case, Ehux has to keep on evolving new adaptations to keep the virus from taking over.

One adaptation that Ehux has developed, like many hosts, is called programmed cell death. Once a coccolithophore is infected by a virus, it'll try to stop the spread of the virus by pushing what amounts to a big red self-destruct button. Before the virus can make too many copies of itself and infect other nearby cells, the infected cell shuts down and implodes.

This makes sense for something like a human cell -- because a human is a collection of many cells that have to work together. But single celled organisms go through programmed cell death too. That might not seem to make a lot of sense at first. If you're a single celled being, like an individual Ehux, once you die, that's it. Your genes are kaput. Yet scientists have observed programmed cell death in phytoplankton like Ehux before. They think that sometimes Ehux cells work like a herd, with some members sacrificing themselves for the greater good of the bloom.

But the enemy is running too, of course. Researchers have also found that the Ehux virus can actually hijack the pathway by which Ehux controls programmed cell death. The virus can slow down the self-destruct cycle, or speed it up, depending on what it wants. So Ehux has to evolve another strategy. Which brings us back to Alice, and her friend the Cheshire Cat.

Ehux has two stages in its life - haploid and diploid. The diploid phase is the one we've been talking about most - blooms happen when Ehux is in its diploid phase. The diploid phase is also the phase that the virus infects. Viruses don't recognize the haploid form of Ehux, so they can't infect it.

A few years ago, scientists (including one researcher on this boat) showed that when the virus started attacking diploid Ehux, the surrounding cells would revert to haploid to hide. The scientists called this the "Cheshire Cat" escape strategy since the plankton were literally disappearing from sight to avoid being infected.

The race continues on and on.

All these different adaptations and alterations are complex and somewhat mysterious. That's what a big part of this research cruise is really about -- figuring out what exactly is going on between Ehux and EhV-86. What makes some strains of Ehux resistant to the virus, and others susceptible? How does the virus control its host, and how is the host evolving to counteract that?

Do the scientists have any idea about how to combat the virus and prevent its spread among the phytoplankton? Paola from Puerto Rico

The arms race we're talking about here is one that's evolved over something like millions of years. Scientists aren't trying to figure out how to stop the virus from infecting Ehux. They're simply trying to understand how it does so, and what factors might change how successful it is. For example, what would happen if the ocean gets warmer? Or it changes in pH or saltiness? These are all things that might happen in the coming years due to climate change. Because Ehux -- and coccolithophores like it -- are so important to Earth's climate, temperature and cloud cover, changes in the interactions between phytoplankton and viruses could have a big effect on our world.

During this trip, I’ll be answering your questions about the science, this boat, and life onboard. Want to know how we search for plankton, why we’re here, or what the food is like? Just ask me! And if you’re wondering how I got here, check out the groups that made this adventure possible: Mind Open Media and COSEE NOW.

Previously in this series:

All Aboard: how you can be a part of our research blog

You wanted to know: what are these phytoplankton?

You wanted to know: what am I bringing to sea?

Greetings from Ponta Delgada! We set sail tomorrow.

Steaming North: how the scientists are trying to find plankton

The superstar sensor: what is a CTD?

Status Update: Day 3 at the Cyclonic Eddy

You wanted to know: what is this virus that infects the phytoplankton (Part One)


The views expressed are those of the author and are not necessarily those of Scientific American.

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