Viruses on glaciers highlight evolutionary mechanism to overcome host
defenses

Date:
September 2, 2020
Source:
University of Innsbruck
Summary:
Scientists studying life on the surface of glaciers in the Arctic
and Alps challenge assumptions on virus evolution. Their study shows
that, contrary to expectations, the viruses on glaciers in the Alps,
Greenland and Spitsbergen are remarkably stable in the environment.



FULL STORY ========================================================================== Viruses are often thought of as a human problem, however they are the
most abundant biological entities on the planet. There are millions of
viruses in every teaspoon of river, lake or seawater, they are found
everywhere there is life and probably infect all living organisms. Most
are completely harmless to humans and infect microscopic animals, plants
and bacteria, which they hijack and reprogram to produce new virus
particles, most often destroying these cells in the process. Every day,
viruses destroy huge number of microorganisms in the environment, which
changes the flow of energy in food webs on global scales.

"Understanding how viruses evolve and function allows us to predict
their role in the environment and how they interact with their hosts,"
says Christopher Bellas from the Department of Ecology at the University
of Innsbruck. Together with colleagues from the Universities of Bristol, Reading and Aberystwyth in the UK, the University of Minnesota, USA,
and Aarhus University in Denmark, he has sequenced and compared genomes
(their total DNA) of viruses which infect microbes found on the surface of glaciers. The study, now published in the journal Nature Communications,
shows that the viruses on glaciers in the Alps, Greenland and Spitsbergen
have genomes which are nearly identical between these isolated locations,
this contradicts what we know about the rapid evolution of viruses.


========================================================================== Evolutionary arms race It is known from laboratory studies that
viruses evolve rapidly in order to keep up with their hosts, which
are also simultaneously evolving defenses against virus infection,
this evolutionary arms race means that they should remain in balance
relative to each other. This is known as the 'Red Queen' hypothesis
after the character from Alice in Wonderland who states: It takes all
the running you can do, to keep in the same place. "This means that
when we sequence the genomes of viruses from two, long-term, isolated
places, we should never find exactly the same virus genomes twice," says Christopher Bellas. The viruses studied by the research team originate
in very unusual habitats on the surface of glaciers and ice sheets,
called cryoconite holes. These small pools of meltwater on glaciers
are ideal places to test how viruses evolve because they are miniature, replicated communities of microbes which are found on widely separated
glaciers around the world.

A genetic fruit machine When the researchers looked at the virus genomes
from isolated cryoconite holes, thousands of kilometers apart, they
expected to find that they would each contain different viruses only
distantly related to one another. What they actually found was that most bacterial infecting viruses (bacteriophages) were nearly identical between
the Arctic and the Alps. However, when they looked closer at their stable genomes, they saw that there were many small sections in each genome
where DNA from other related viruses was repeatedly swapped in and out,
in a known process called recombination. In each different location, the viruses shuffled the genes present in these swappable regions like a kind
of genetic fruit machine. "This means that in the natural environment,
gene swapping between viruses by recombination creates much diversity
in the virus population, specifically in genes which are involved in recognising and attaching to different hosts, this probably gives viruses
the potential to quickly adapt to different hosts in the environment,"
explains Christopher Bellas.


========================================================================== Story Source: Materials provided by University_of_Innsbruck. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christopher M. Bellas, Declan C. Schroeder, Arwyn Edwards,
Gary Barker,
Alexandre M. Anesio. Flexible genes establish widespread
bacteriophage pan-genomes in cryoconite hole ecosystems. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-18236-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200902095126.htm

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