October 6, 2018 – Like bacteria, the word “virus” often conjures up images of sickness and death. However, relatively few of the many types of viruses cause problems for humans. None of the thermophilic viruses in Yellowstone should cause problems for human health—our bodies are too cold, for one thing.
Unlike microorganisms in the three domains, viruses are not considered to be alive. (Yet they are still called “life forms.”) They have no cell structure, only a protein “envelope” that encloses a piece of genetic material. They cannot reproduce on their own. Instead, a virus inserts itself into a host cell and uses that cell’s nutrients and metabolism to produce more viruses.
Scientists suspect many viruses exist in Yellowstone’s hydrothermal features because they would be a logical part of the thermophilic ecosystem. One kind was discovered in Congress Pool, at Norris Geyser Basin. It was infecting the archaeum Sulfolobus. Another kind of virus has been identified in pools near Midway Geyser Basin.
Archaea are the most extreme of all extremophiles—some kinds live in the frigid environments of Antarctica, others live in the boiling acidic springs of Yellowstone. These single-celled organisms have no nucleus, but have a unique, tough outer cell wall. This tough wall contains molecules and enzymes that may keep acid out of the organism, allowing it to live in environments of pH 3 or less. (Vinegar, for example, has a pH of less than 3.) Archaea also have protective enzymes within their cells.
Montana State University scientists have found a new lineage of microbes living in Yellowstone National Park’s thermal features that sheds light on the origin of life, the evolution of archaeal life and the importance of iron in early life.
Professor William Inskeep and his team of researchers published their findings May 14 in the scientific journal Nature Microbiology.
The scientists called the new archaeal lineage Marsarchaeota after Mars, the red planet, because these organisms thrive in habitats containing iron oxides. Within Marsarchaeota, they discovered two main subgroups that live throughout Yellowstone and thrive in hot, acidic water where iron oxide is the main mineral. One subgroup lives in water above 122 degrees Fahrenheit, and the other lives in water above 140 to 176 degrees. The water is about as acidic as grapefruit juice. Their microbial mats are red because of the iron oxide.
“It’s interesting that the habitat of these organisms contains (iron) minerals similar to those found on the surface of Mars,” Inskeep said.
He added that microbes produce iron oxide, but the Marsarchaeota do not. They might be involved in reducing iron into a simpler form, “which is important from an early Earth standpoint. Iron cycling has been implicated as being extremely important in early Earth conditions.”
The Marsarchaeota live fairly deep in microbial mats, but they still require low levels of oxygen, Inskeep said. The subgroups are so abundant that, together, they can account for as much as half of the organisms living within a single microbial mat.
The scientists studied microbial mats throughout Yellowstone. Microorganisms in these “microbial beaver dams” produce iron oxide that creates terraces, which, in turn, block streams. As water (only a couple of millimeters deep) runs over the terraces, oxygen is captured from the atmosphere and supplied to the Marsarchaeota.
“Knowing about this new group of archaea provides additional pieces of the puzzle for understanding high-temperature biology,” he said. “That could be important in industry and molecular biology.”
Some scientists think present-day archaea have not changed much from their ancestors. This may be due to the extreme environments in which they live, which would allow little chance for successful changes to occur. If this is so, modern archaea may not be much different from the original forms—and thus provide an important link with Earth’s earliest life forms.
Once thought to be bacteria, organisms in the domain Archaea actually may be more closely related to Eukarya—which includes plants and animals.
Many kinds of archaea live in the hydrothermal waters of Yellowstone. For example, Grand Prismatic Spring at Midway Geyser Basin contains archaea. They are most well known in the superheated acidic features of Norris Geyser Basin and in the muddy roiling springs of the Mud Volcano area.
Whenever you see a hot, muddy, acidic spring, you are probably seeing the results of a thriving community of archaea called Sulfolobus. This is the archaea most often isolated and most well-known by scientists. In sulfuric hydrothermal areas, it oxidizes hydrogen sulfide into sulfuric acid, which helps dissolve the rocks into mud.
The Sulfolobus community in Congress Pool (Norris) is providing interesting new research directions for scientists: It is parasitized by viruses never before known on Earth.
Norris Geyser Basin is one of the best places to see thermophilic algae. Bright green Cyanidioschyzon grows on top of orange-red iron deposits around Whirligig and Echinus geysers and their runoff channels. Waving streamers of Zygogonium are especially easy to see in Porcelain Basin, where their dark colors contrast with the white surface.
From the boardwalk crossing Porcelain Basin, you can also see larger eukarya, such as ephydrid flies.
They live among the thermophilic mats and streamers, and eat, among other things, algae. The species that lives in the waters of Geyser Hill, in the Upper Geyser Basin, lays its eggs in pink-orange mounds, sometimes on the firm surfaces of the mats. Part of the thermophilic food chain, ephydrid flies become prey for spiders, beetles, and birds.
Some microscopic eukarya consume other thermophiles.
A predatory protozoan, called Vorticella, thrives in the warm, acidic waters of Obsidian Creek, which flows north toward Mammoth Hot Springs, where it consumes thermophilic bacteria.
Thermophilic eukarya include one form that is dangerous to humans: Naegleria, a type of amoeba, that can cause disease and death in humans if inhaled through the nose.
Although they aren’t visible like mushrooms, several thermophilic fungi thrive in Yellowstone.
Curvularia protuberata lives in the roots of hot springs panic grass. This association helps both
survive higher temperatures than when alone. In addition, researchers have recently discovered a virus inside the fungus that is also essential to the grass’s ability to grow on hot ground.
“There are really only three common shapes for viruses (spherical, cylindrical and lemon-shaped),” said co-author Martin Lawrence, a professor in MSU’s Department of Chemistry and Biochemistry in the College of Letters and Science. “We have understood for many years the principles for the construction of cylindrical and spherical viruses, but this is the first time we have really understood how the third class of viruses is put together.
“We now understand how this third kind of virus shell is assembled and the dynamic process it uses to carry and then eventually eject the DNA that it is carrying,” Lawrence said. “This understanding could potentially be adapted for technological uses.
“If we could load these virus shells with a different cargo, say a drug, and target it to a particular place in the body, such as a tumor, it could then deliver the drug to just that specific location, making the drug more effective, or reducing side effects,” Lawrence said.
Hochstein’s collaborators said her research is significant because it contributes to basic understanding and has the potential for broad applications. It also shows what can happen when scientists have access to one of the world’s most sophisticated microscopes. Such microscopes have sparked a revolution in cryo-electron microscopy, for which the developers of the technology won the 2017 Nobel Prize in chemistry.
Co-author Mark Young, a professor in MSU’s Department of Plant Sciences and Plant Pathology in the College of Agriculture, said virologists and scientists interested in nanotechnology were excited to learn about a new way that nature has evolved viruses to build a virus particle.
“The detailed understanding of this virus isolated from a boiling acid hot spring in Yellowstone provides a potentially new virus-based nano-container that can operate at high temperature and acidic conditions which is of interest to biotech companies,” Young said. “This is because it extends the conditions under which virus-based nano-cages can operate. Already, these types of nano-cages have been shown to be stable in the animal GI track, opening the possibility for their development as smart drug delivery systems.”
Lawrence said the research team, among other things, was able to discover how the Acidianus virus makes a “remarkable transition” from a lemon-shaped virus into long, thin cylinders. Explaining how, he compared its structure to bricks connected by ropes.
“The bricks are actually connected to each other in long spirals, almost like a spiraling rope, and four to six of these spiraling ropes then wrap around each other to make the lemon-shaped container,” Lawrence said.
To turn the lemon-shaped viruses into cylinders, the ropes have to slide against each other, Lawrence said.
“We think this transition is used to squirt the DNA from the virus into the cell that the virus is infecting,” Lawrence said. “This answers the question of how the DNA leaves the virus. By analogy, how does one get juice out of a lemon? You squeeze it. In this case, the ropes in the shell squeeze the DNA inside, forcing it out.”
Lawrence praised Hochstein for her years working in Yellowstone National Park and her involvement in every other phase of the research. Acidianus doesn’t grow in the lab, so Alice Springs in Yellowstone Park’s Crater Hills became her laboratory, Lawrence said.