From the Lab to the Ocean

Phytoplankton – plant-like single-celled organisms that float in water – are vital to the health of the planet, according to Dr. Assaf Vardi, who recently joined the Institute’s Plant Sciences Department. “We can thank phytoplankton for every second breath we take. Even though they make up just 0.5% of Earth’s biomass, phytoplankton rival the planets’ rainforests when it comes to absorbing carbon dioxide and releasing oxygen ^_ they carry out about half the photosynthesis on the planet.” And these microorganisms, whose name means “plant drifters” in Greek, are the base of the marine food chain: Without phytoplankton, there would be no life in the ocean. On the other hand, for reasons that aren’t completely understood, their reproduction sometimes gets out of hand, producing algal blooms that can extend hundreds and thousands of kilometers. Some of these blooms simply choke off waterways, while others, among them the infamous “red tides,” produce neurotoxins that kill fish and work their way up the food chain, where they can be toxic to livestock and humans worldwide.

 

 

Agricultural and sewage runoff, as well as and other forms of pollution, are currently increasing the severity of harmful algal blooms in lakes and near coastal waters. Moreover, climate change is likely to increase ocean temperatures and reduce the mixing between layers that now helps dispel harmful algal blooms. In research that takes him from the lab bench to the open ocean, Vardi is attempting to unravel the complex ecology of these organisms by investigating their genes and the signals they produce to cope with their ever-changing environment, especially those involving algal blooms. In recent research in fjords along Norway’s coastline, he was even able to induce algal blooms in a controlled setting, using specialized facilities there to investigate the process. His research subjects include diatoms, whose glassy shells sport an endless variety of intricate shapes, and coccolithophores, whose calcium carbonate-based shells make them active participants in the global carbon cycle.

A Meeting of Science and Art     After earning a Ph.D. in molecular ecology from the Hebrew University of Jerusalem in 2004, Dr. Assaf Vardi conducted postdoctoral research at the Ěcole Normale Supĕrieure, Paris, and Rutgers University. He joined the Weizmann Institute faculty in 2010, and he has also been appointed an adjunct scientist at Woods Hole Oceanographic Institution.   Vardi is married to the artist Nivi Alroy, who borrows concepts from Vardi’s scientific research on apoptosis and cell-cell communication and reinterprets them in her sculptures. The couple recently collaborated on a children’s book that explains ecology through the lives of microorganisms in a drop of water from the ocean.

In his postdoctoral research, Vardi found that viruses are responsible for the disappearance of the algal blooms. But when he and his colleagues looked closely at the genetic sequences of both phytoplankton and virus, they found some surprises that led them to formulate new theories about their ecology and evolution. For instance, they discovered evidence for apoptosis – cell suicide – in the microorganisms. Apoptosis is ubiquitous in multi-celled organisms: Damaged or used-up cells die so that the whole may live. So why would a single-celled microorganism commit suicide? One explanation, says Vardi, is that the genes for cell death might have coevolved in both host and virus to prevent the virus from infecting and killing off all the phytoplankton – an evolutionary dead end. On the other hand, viruses may be recruiting the host cells’ death machinery to bud out after completing their replication cycle inside the cell. This could explain why the viruses seem to have genes previously seen only in host organisms.