Jellyfish-Like Parasite Found in Salmon is the First Organism Able to Live Without Oxygen

The basic idea that all living organisms require oxygen in order to live might have been proven wrong by a unique creature that seems to survive without needing to breathe. The organism, a parasite looking like a jellyfish, is the first molecular entity that doesn’t have a mitochondrial genome, meaning it lives without needing oxygen.

The new finding changes the definition of what an organism can be and can impact the search for extraterrestrial life as well. The small parasite survived in salmon tissue and developed so that it doesn’t require oxygen in order to generate energy.

Life in the Beginning

More than 1.45 billion years ago, life was believed to start developing the capacity to metabolize oxygen or to respirate. A larger archaeon and a smaller bacterium formed a symbiotic connection when the archaeon swallowed the bacterium and made the relationship beneficial for both of them.

Ultimately, this relation has led to the two organisms developing together, and those bacteria hidden inside became the mitochondria, a cell organ that is crucial for energy production in a cell. It has a vital role in the respiration process and is present in large numbers in every cell of the body, apart from red blood cells. They transform oxygen and nutrients into a molecule known as adenosine triphosphate (ATP) that nurtures the cell’s metabolic processes.

Even though some organisms have adjusted to survive and develop in a low-oxygen or hypoxic setting, with some single-celled creatures that have even developed organelles related to mitochondria for anaerobic metabolism, it has been a topic of scientific arguments whether there is actually a chance of a solely anaerobic multicellular organism.

Now, researchers from Tel Aviv University in Israel, led by Dayana Yahalomi, discovered the peculiar fact on the common salmon parasite known as Henneguya salminicola.

Surviving in a Hypoxic Setting

H. salminicola [Image: Stephen Douglas Atkinson]
The parasite is a cnidarian, which is a member of the same category as corals, jellyfish, and anemones. They live inside the salmon and feeds with ready-made nutrients rather than consuming oxygen on their own. They are not dangerous to humans, some researchers say, even though they create hideous cysts in the salmon’s flesh.

Those organisms are able to survive hypoxic conditions inside its host, which surprised experts. Stephen Atkinson, a senior research associate at the Department of Microbiology at Oregon State University, and the co-author of the paper said that when thinking about creatures, we imagine a multicellular organism that needs oxygen in order to survive. However, when it comes to this parasite, there’s at least one multicellular being that doesn’t have the genetic possibility to use oxygen.

The team of researchers used deep sequencing and fluorescence microscopy to analyze the H. salminicola, and they discovered that it lost its mitochondrial genome but developed some folds in the inner membrane not usually found in organisms. They also maintained a weirdly complex structure that resembles a jellyfish stinging cells to attach to their hosts.

The study could help also help fisheries change their methods in rearing salmon in order to deal with the parasite as no one wants to eat salmon filled with tiny peculiar jellyfish, although they are supposedly safe to ingest.

The paper has been published in PNAS.

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