Some truths about the universe seem immutable. Breathing oxygen is considered, for example, a key characteristic of multicellular animals, but what if that animal does not breathe? Until now it was not believed possible, but a team of scientists from Tel Aviv University (Israel) has discovered exactly that: an animal that does not breathe oxygen.
Life began to develop the ability to metabolize oxygen, that is, to breathe, sometime more than 1.45 billion years ago . We know that there are adaptations that allow some organisms to thrive in low oxygen or hypoxic conditions, such as the fascinating tardigrades that, in different experiments, have emerged alive from subzero temperatures or the oxygen-free vacuum of space but the presence of exclusively anaerobic multicellular organisms. it has been the subject of scientific debate. Up to now.
What animal is?
It is a small parasite of less than 10 cells called Henneguya salminicola that lives in the muscle of salmon. It belongs to the superior classification of cnidarians, a phylum of relatively simple diblastic animals that live exclusively in aquatic environments, mostly marine. As it evolved, this unusual animal, which is a myxozoan relative of jellyfish and corals, stopped breathing and consumed oxygen to produce energy (as if it were its “gasoline”). It is the first multicellular organism that we find that does not breathe; its life does not depend on oxygen.
“Aerobic respiration was believed to be ubiquitous in animals, but now we confirm that this is not the case,” explains study co-author Dorothee Huchon. “Our discovery shows that evolution can go in strange directions. Aerobic respiration is an important source of energy, and yet we found an animal that left this critical path .”
The new study, published in the journal Proceedings of the National Academy of Science (PNAS) and led by Dayana Yahalomi, focused directly on this salmon parasite, as they suspected that it could have anaerobic respiration. These parasites are not harmful and live with salmon throughout their life cycle.
Accidental discovery
The scientists used deep sequencing and fluorescence microscopy to conduct a detailed study of H. salminicola and found that it had lost its mitochondrial genome and aerobic respiration capacity and nearly all of the nuclear genes involved in mitochondrial transcription and replication . The same sequence and microscopic methods were employed in a closely related cnidary fish parasite, Myxobolus squamalis, as a control specimen and clearly showed a mitochondrial genome. The results showed a multicellular organism that does not need oxygen to survive. How it manages to survive without oxygen remains a mystery.
Other organisms, such as fungi or amoebae in anaerobic environments have lost the ability to breathe over time, but this work shows that it can also happen to animals, possibly because the parasite lives precisely in an environment without oxygen.
Research implications
“Our discovery confirms that adaptation to an anaerobic environment is not unique to single-celled eukaryotes, but has also evolved into a multicellular parasitic animal,” the authors wrote.
This finding not only modifies our understanding of how life can work here on Earth, it could also have implications for the search for extraterrestrial life.
The genome of this parasite was sequenced, along with those of other Myxozoan fish parasites, as part of research supported by the US-Israel Binational Science Foundation.
Referencia: Dayana Yahalomi, Stephen D. Atkinson, Moran Neuhof, E. Sally Chang, Hervé Philippe, Paulyn Cartwright, Jerri L. Bartholomew, Dorothée Huchon. A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome. Proceedings of the National Academy of Sciences, 2020; 201909907 DOI: 10.1073/pnas.1909907117
