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‘Gatling Gun’ Plankton Reveals Violent Microbial World

New research gives us the first hi-res videos of a bizarre, microscopic arms race.

Watch Plankton "Harpoon" Their Prey

Is the bizarre blob in this video animal, vegetable, or mineral?

Actually, it's none of the above—these single-celled organisms are dinoflagellates, a type of protist that seems to bear more resemblance to aliens than to Earthly life forms.

“Looking at these cells under the microscope...they're like spaceships scudding around with armor-plated exteriors,” says Greg Gavelis, a biologist who researched these creatures while at the University of British Columbia. “They'll bump into each other, shoot little volleys of missiles at each other.”

In fact, these oceanic plankton are engaged in a heated arms race. Gavelis and his colleagues recently published a paper describing the especially warlike adaptations of two particular genera of dinoflagellates, Polykrikos and Nematodinium. (Read "Parasitic Bird Fights Evolutionary Arms Race...With Itself")

Through painstaking work—the researchers had to collect cell samples in the wild, only about one in three of which was usable—Gavelis and his fellow researchers were able to build the first 3D models of the ballistic mechanisms these genera use to attack other dinoflagellates.

Polykrikos cells have a capsule, called a nematocyst, that contracts to propel a sharp stylet through the water—and through the armor of another microbe. A tubule connected to the stylet acts as a tow line, which the predatory cell uses to draw the prey cell close enough to strike—at which point the predatory cell actually unzips its own cell membrane to engulf the prey cell.

Nematodinium has a very similar nematocyst. Or rather, it has 11 to 15 nematocysts arranged in a ring that all launch simultaneously, earning it the “Gatling gun” nickname.

“The Gatling gun kind of seems like overkill,” admits Gavelis. “But if you really want to eat dinoflagellates, you’ve got to bring some weapons to the fight” to overcome the hard silica armor, toxic spikes, and various projectiles these organisms use to defend themselves.

All of this cellular conflict happens on an incredibly microscopic scale: to put it in perspective, the average human being is to a blue whale what a dinoflagellate cell is to a millimeter. (Learn why microbes hold the key to life on earth.)

Researchers initially thought these nematocysts might be genetically similar to those of cnidarians, animals such as jellyfish and sea anemones. Even though cnidarians’ and dinoflagellates’ most recent common ancestor lived over a billion years ago, putting them about as far apart on the evolutionary tree as it’s possible to go, they are the only organisms found to use nematocysts. (Watch this octopus eat a jellyfish, then use it as a weapon.)

However, to their surprise, the researchers found that the similar nematocysts are an example of convergent evolution, rather than a shared genetic trait. In fact, the plankton’s ballistic mechanisms are actually much more complex than those of cnidarians.

Dinoflagellates’ incredible diversity of traits and behaviors is what makes them so worthwhile to research. “Any rule that you come up with in biology, there's some sort of exception that you'll find in dinoflagellates,” says Brian Leander, a zoologist and the senior author of the study. More species of “dinos” are being discovered every month.

Even aside from the joy of discovery Leander describes as an “adrenaline rush,” microbial research can have outsized impacts. Polykrikos are now understood to predate several kinds of microbes responsible for toxic algal blooms. And pioneering medical applications show that planktonic compounds can be used as a chemotherapeutic against melanoma, or even as microscopic syringes that deliver drugs directly to a patient's cells.

For Leander, a teacher, it’s all about the human angle. “That's a huge reward—the exploration of this biodiversity through the eyes of people who are just starting out in their careers in science,” he says. “I absolutely love it.”

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