Microscopic Titans: How Viruses Spread at Nature’s Extreme
By: Christine Wendling
In the annals of scientific history, aquatic viruses have only begun to be studied recently. Scientists did not discover that viruses were present in very high abundances in the ocean until 1989, and they are as mysterious as they are extreme. Jennifer R. Brum, assistant professor in the Department of Oceanography and Coastal Sciences, is studying the ecological and biogeochemical impacts of aquatic viruses that infect bacteria in one of the most extraordinary environments on Earth—hydrothermal vents.
Viruses are microscopic, infectious agents made up of a DNA or RNA core that replicate within the cells of living hosts, often until inducing cell lysis, or dissolution. Then, after the carnage, they move on to another cell or host. Most viruses are smaller than a bacterial cell, only about 50 nanometers, and they often infect bacteria just like they infect humans.
Hydrothermal vents are intensely hot cracks in the sea floor that spew geothermally heated water capable of exceeding 750°F; however, the mineral-rich water will not boil due to the crushing pressure in the deep ocean. To collect samples, Brum uses a remotely operated vehicle (ROV) that can withstand the extreme temperature and pressure of the vents. The ROV has been outfitted with a metal rack housing six open-ended bottles that hold five liters each. It carries the rack over to the desired location and snaps the bottles closed, entrapping the water and viruses within. Once the rack is brought back to the surface, Brum stains the viruses’ nucleic acid, which causes them glow. Then, she can observe them using epifluorescence microscopy and count them. She views more detailed images of the virus using a transmission electron microscope as well.
Brum has discovered strange virus behavior while collecting samples from five hydrothermal vents in the Atlantic Ocean. So far, her preliminary data suggests that some viruses in hydrothermal vents are capable of making calculated decisions about when to kill their host bacteria, behavior not unlike that of viruses she studied in Antarctica previously.
“Basically, [some viruses in Antarctica] would hold over winter in their host. Then, when spring came and their host became productive—boom, they would kill the host. And, it might have been mutually beneficial. The virus helps the host survive the winter and the host helps the virus survive the winter. Think of it like an armistice in war. Then, when spring arrives, they go back to killing each other again,” Brum stated.
Brum’s work with hydrothermal vents may not only have an impact on our ability to predict future viral behaviors as they adapt and mutate but also have extraterrestrial applications. One of the drivers of NASA’s astrobiology program, or exobiology, is the idea that the more extreme environments on Earth may mimic environments we find elsewhere. And, with the help of an astrobiologist, Brum is currently writing a proposal to study hydrothermal vents on Earth as an analog for vents that are thought to exist elsewhere in the universe. There is considerable evidence now that there are active hydrothermal vents on Europa, Jupiter’s smallest moon. Scientists have captured images of spray from hydrothermal vents erupting through cracks on Europa’s surface, which is covered in ice.
As of now, scientists have not sampled the ocean beneath Europa’s icy surface, but if they could obtain a sample and discover viruses and bacteria there, it would have huge ramifications on scientific thought about extraterrestrial life. In fact, some believe hydrothermal vents are where life originated on our planet, and the presence of viruses there indicate they may have played a role in the evolution of life on Earth.
“The reason why hydrothermal vents are thought to be where life originated is because they have this special chemical and electron gradient. People have actually generated RNA in artificial glass globes by making a little artificial hydrothermal vent. So there is considerable evidence, although we will never know for sure. That's part of the exploratory, fun part of doing research,” Brum said.