Viruses are often considered a human problem, but they are the most numerous biological objects on the planet. There are millions of viruses in every teaspoon of river, lake, or seawater, they are found wherever life is, and they probably infect all living organisms. Most of them are completely harmless to humans and infect microscopic animals, plants, and bacteria, which they capture and reprogram to produce new viral particles, most often destroying these cells in the process. An international team of scientists conducted an experiment by sequencing and comparing the genomes (their shared DNA) of viruses that infect microbes found on the surface of glaciers. The study, published in the journal Nature Communications, shows that viruses on glaciers in the Alps, Greenland, and Svalbard have genomes that are nearly identical in these isolated locations, which contradicts what we know about the rapid evolution of viruses.
Every day, viruses destroy a huge number of microorganisms in the environment, which is changing the flow of energy in food webs on a global scale. “Understanding how viruses develop and function allows us to predict their role in the environment and how they interact with their hosts,” explains Christopher Bellas from the Department of Ecology at the University of Innsbruck.
It is known from laboratory research that viruses evolve rapidly to keep up with their hosts, which simultaneously develop defenses against viral infection. This evolutionary arms race means they must remain in equilibrium with each other. This is known as the “Black Queen” hypothesis after the character from “Alice in Wonderland”. The Red Queen hypothesis, also called the Black Queen Principle, the Black Queen Effect, or the Black Queen Race (Run), is an evolutionary hypothesis. It can be formulated as follows: “Regarding the evolutionary system, the species needs constant change and adaptation in order to maintain its existence in the surrounding biological world, which is constantly evolving with it”.
The viruses the research team is studying come from very unusual habitats on the surface of glaciers and ice sheets – cryoconite holes. These small pools of meltwater on glaciers are ideal places to test the evolution of viruses because they are miniature reproducible communities of microbes that are found on far-apart glaciers around the world.
When the researchers examined the genomes of viruses from isolated cryoconite holes thousands of kilometers apart, they expected to find that each would contain different viruses, only distantly related to each other. In fact, they found that most bacterial infectious viruses (bacteriophages) are virtually identical in the Arctic and Alps. However, when they looked closely at their stable genomes, they saw that each had many small regions where the DNA of other related viruses was repeatedly swapped as part of recombination. In every other location, viruses have shuffled the genes present in these exchangeable regions.
“This means that in the wild, the exchange of genes between viruses by recombination creates a lot of diversity in the viral population, especially in genes that are involved in recognition and attachment to different hosts. This probably gives viruses the ability to quickly adapt to different hosts in the environment, ”concludes Christopher Bellas.