The Deep Blue

Of algae and people

Phytoplankton can sometimes, for unknown reasons, multiply very rapidly. This causes algal blooms that can extend for hundreds, and even thousands, of kilometers – large enough to be seen from space. And then, all at once, the bloom collapses and disappears. Understanding how these blooms grow and collapse is critical: The oceans’ phytoplankton absorb as much carbon dioxide as the world’s rain forests, so they could be important allies in the effort to reduce global warming; and the sustenance they supply to the marine food chain is vital for keeping the world’s population fed.

Vardi and his colleagues had previously discovered that viruses are responsible for algal bloom collapse. Like viruses everywhere, these invaders insert their genes into their host’s cells. In the case of those that attack the phytoplankton, these virus genes produce enzymes that, in turn, produce fat molecules called sphingolipids. Interestingly enough, these sphingolipids are very similar to certain human ones that have been implicated in a number of diseases, but they had never been found to be produced by viruses. Vardi: “These enzymes and mechanisms have been conserved throughout evolution, and they function in an extremely wide variety of organisms.”

Vardi had discovered a cellular mechanism in the phytoplankton that senses the accumulation of sphingolipids and initiates a programmed cell death sequence called apoptosis. Apoptosis is well-known in multicellular organisms: Damaged or used-up cells take their own lives for the good of the whole. But what use is cell suicide to a single-celled organism? How do the cells withing the phytoplankton community communicate so that some survive, even as others lose their lives? How does this affect the ecology of the oceans as a whole? These are a few of the questions that the researchers on board have been attempting to clarify.

According to recent findings of Vardi and others, phytoplankton are actually not so keen on the idea of suicide, and they at first resist the invading tide of viruses with an entire arsenal. In a dramatic evolutionary arms race, they fight with chemical weapons, military maneuvers, head-on attacks and evasive end runs – all conducted on the molecular level within the phytoplankton cells. Multiplied by billions of cells, such molecular processes can determine the very course of the earth’s bio-geochemical pathways and, ultimately, the climate. And the fact that these pathways have been preserved throughout evolution means that researchers can study them in phytoplankton and apply them to humans. For instance, certain substances these marine organisms use to fight viral invasion might be effective against those that cause disease in humans, while research into the mechanisms of cell death in these simple creatures could lead to new ways of initiating cell death – in cancer cells, for instance.