Scientists shed new light on viruses' role in coral bleaching

Date:
October 14, 2020
Source:
Oregon State University
Summary:
Scientists have shown that viral infection is involved in coral
bleaching - the breakdown of the symbiotic relationship between
corals and the algae they rely on for energy.



FULL STORY ========================================================================== Scientists at Oregon State University have shown that viral infection is involved in coral bleaching -- the breakdown of the symbiotic relationship between corals and the algae they rely on for energy.


========================================================================== Funded by the National Science Foundation, the research is important
because understanding the factors behind coral health is crucial to
efforts to save the Earth's embattled reefs -- between 2014 and 2017
alone, more than 75% experienced bleaching-level heat stress, and 30%
suffered mortality-level stress.

The planet's largest and most significant structures of biological origin, coral reefs are found in less than 1% of the ocean but are home to nearly
one- quarter of all known marine species. Reefs also help regulate the
sea's carbon dioxide levels and are a vital hunting ground that scientists
use in the search for new medicines.

Since their first appearance 425 million years ago, corals have branched
into more than 1,500 species. A complex composition of dinoflagellates
-- including the algae symbiont -- fungi, bacteria, archaea and viruses
make up the coral microbiome, and shifts in microbiome composition are connected to changes in coral health.

The algae the corals need can be stressed by warming oceans to the point
of dysbiosis -- a collapse of the host-symbiont partnership.

To better understand how viruses contribute to making corals healthy or unhealthy, Oregon State Ph.D. candidate Adriana Messyasz and microbiology researcher Rebecca Vega Thurber of the OSU College of Science led a
project that compared the viral metagenomes of coral colony pairs during
a minor 2016 bleaching event in Mo'orea, French Polynesia.



==========================================================================
Also known as environmental genomics, metagenomics refers to studying
genetic material recovered directly from environmental samples, in this
case samples taken from a coral reef.

For this study, scientists collected bleached and non-bleached pairs
of corals to determine if the mixes of viruses on them were similar or different. The bleached and non-bleached corals shared nearly identical environmental conditions.

"After analyzing the viral metagenomes of each pair, we found that
bleached corals had a higher abundance of eukaryotic viral sequences, and non-bleached corals had a higher abundance of bacteriophage sequences," Messyasz said. "This gave us the first quantitative evidence of a shift
in viral assemblages between coral bleaching states." Bacteriophage
viruses infect and replicate within bacteria. Eukaryotic viruses infect non-bacterial organisms like animals.

In addition to having a greater presence of eukaryotic viruses in
general, bleached corals displayed an abundance of what are called giant viruses. Known scientifically as nucleocytoplasmic large DNA viruses,
or NCLDV, they are complex, double-stranded DNA viruses that can be
parasitic to organisms ranging from the single-celled to large animals, including humans.

"Giant viruses have been implicated in coral bleaching," Messyasz
said. "We were able to generate the first draft genome of a giant virus
that might be a factor in bleaching." The researchers used an electron microscope to identify multiple viral particle types, all reminiscent
of medium- to large-sized NCLDV, she said.

"Based on what we saw under the microscope and our taxonomic annotations
of viral metagenome sequences, we think the draft genome represents
a novel, phylogenetically distinct member of the NCLDVs," Messyasz
said. "Its closest sequenced relative is a marine flagellate-associated
virus." The new NCLDV is also present in apparently healthy corals
but in far less abundance, suggesting it plays a role in the onset of
bleaching and/or its severity, she added.


========================================================================== Story Source: Materials provided by Oregon_State_University. Original
written by Steve Lundeberg. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Adriana Messyasz, Stephanie M. Rosales, Ryan S. Mueller, Teresa
Sawyer,
Adrienne M. S. Correa, Andrew R. Thurber, Rebecca Vega
Thurber. Coral Bleaching Phenotypes Associated With Differential
Abundances of Nucleocytoplasmic Large DNA Viruses. Frontiers in
Marine Science, 2020; 7 DOI: 10.3389/fmars.2020.555474 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014082804.htm

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