How Phytoplankton Die: They Catch a Virus; Common phytoplankton 'leave the light on' for their own killers

How Phytoplankton Die: They Catch a Virus; Common phytoplankton 'leave the light on' for their own killers


Common phytoplankton leave the light on for their own killers


New Brunswick, N.J. Scientists at Rutgers, The State University of New Jersey, have discovered how phytoplankton die. Knowing the process by which phytoplankton expire is important to research on climate change, because of the role they play in regulating oxygen content of the atmosphere and in consuming carbon dioxide, a major greenhouse gas.

In a paper published this week in the Proceedings of the National Academy of Sciences, Kay Bidle, assistant professor of marine science at Rutgers Institute of Marine and Coastal Sciences, and his co-authors report that one of the oceans most common phytoplankton, Emiliania huxleyi, has an innate suicide pathway that is activated by specific viruses.

E. huxleyi is one of the oceans most common phytoplankton, found in every ocean but the Arctic Ocean and the waters of Antarctica. Its blooms often grow to cover 200,000 square kilometers and can be seen by satellites from space. It performs its death ritual once viruses infect the unicellular organism, ultimately killing it. .

The death machinery consists of enzymes that, once activated by viral infection, trigger apoptosis, or programmed cell death. We knew that phytoplankton died, or turned over rapidly in the ocean every week, but we didnt know how, Bidle said. We now know that viral infection activates and utilizes components of the cell death machinery in these organisms, and we know how the viruses infect these cells.

In their laboratory, Bidle (rhymes with idle) and his colleagues infected specimens of E. huxleyi with viruses they knew to have a host/parasite relationship with the phytoplankton. Viruses are the most abundant biological entities in the oceans, and they are vital in turning over the 95 percent of the oceans biomass that consists of microbes, like phytoplankton, Bidle said. He said that phytoplankton, essentially, left the light on for incoming viruses, which sought them out, invaded them, took them over, reproduce rapidly, kill the host, and release more viruses to kill more phytoplankton. The lights are metacaspases, enzymes that facilitate the infection.

But not always: Bidle and his colleagues also discovered that some E. huxleyi strains have the power to leave the light off to resist the efforts of the virus to start up the cell death machinery.

In nature, E. huxleyi and its viral parasites are engaged in a constant competition, Bidle said. The phytoplankton develop ways to shut down their metacaspases and thus fend off the virus; the virus develops ways to turn them on and infect its host. This is whats known in ecology as the Red Queen effect, Bidle said. In Lewis Carrolls Through the Looking Glass, the Red Queen tells Alice, It takes all the running you can do to keep in the same place.

E. huxleyi is very common, but its only one of many species of phytoplankton in the oceans. If each species has its own virus, then each species of phytoplankton is in continuing, never-ending war with its own virus.

But, bearing the Red Queen effect in mind, there is no such thing as total victory for either side, Bidle said. Even if a virus could kill off almost all its phytoplankton, a few resistant organisms would survive, and the phytoplankton would come back eventually.

Bidles co-authors are Paul Falkowski, professor of geological and marine sciences at Rutgers; Liti Haramaty, a researcher in Bidles laboratory; and Joana Barcelos e Ramos, of the Leibniz Institute of Marine Sciences in Kiel, Germany.

Contact: Ken Branson

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