All previously discovered living things on earth are classified into five kingdoms under the taxonomical system. For example, all animals belong to Kingdom Animalia, plants belong to Plantae, fungi to Kingdom Fungi, protists to Protista, with bacteria and archaea belonging to their own taxonomic rank known as Kingdom Monera. As bacteria are unicellular prokaryotic entities, they do not have a nucleus or any membrane-bound organelles. In contrast, plants and animals consist of eukaryotic cells containing a nucleus and membrane-bound organelles such as mitochondria, where aerobic respiration takes place. Aerobic respiration is a hallmark of multicellular eukaryotes requiring the intake of oxygen in order to create the chemical adenosine triphosphate (ATP), that provides energy to the cell. Conversely, anaerobic respiration is the process of producing cellular energy without oxygen only seen in prokaryotic bacteria and single-celled eukaryotes. Now, a study from researchers at Tel Aviv University discovers the first-ever multicellular animal that doesn’t need oxygen to survive. The team states their data shows H. salminicola, a microscopic parasite, is a multicellular animal with no mitochondrial DNA, meaning it can exist without the need to breathe oxygen. The study is published in the journal Proceedings of the National Academy of Sciences.
Previous studies show aerobic respiration is the process by which all oxygen-breathing organisms on earth turn food, such as proteins, fats, and sugars, into energy. The product of respiration is the molecule ATP, using the energy stored in its phosphate bonds to power chemical reactions the cell needs to survive. The generation of ATP from oxygen takes place in mitochondria which contain their own genome separate from the genomic material held within the cell nuclei, an indication they were acquired from bacteria through symbiosis. The current study identifies a eukaryotic parasite, related to the jellyfish, containing no mitochondrial DNA making it completely free of oxygen dependency.
The current study sequences the DNA of the H. salminicola parasite to reveal the absence of mitochondrial genes. Results were verified using the same methods to sequence the DNA of the closely related M. squamalis, indicating its mitochondrial genome was intact unlike it’s relative H. salminicola. Data findings observe the presence of structures resembling mitochondria in H. salminicola incapable of producing the enzymes necessary for respiration, strongly suggesting the organism is capable of surviving without oxygen.
The lab explains H. salminicola is part of the myxozoa class, a subgroup of multicellular aquatic parasites related to the jellyfish. They go on to hypothesize H. salminicola once looked like a jellyfish, devolving to lose most of its multicellular characteristics, including the lack of respiratory genes. They conclude their data providing proof of the presence of structures resembling mitochondrial DNA suggesting the parasites have in fact undergone the process of de-evolution, losing tissue, nerve cells, and muscles, as well as the ability to breathe oxygen.
The team surmises they have discovered a multicellular animal, H. salminicola that has devolved to lose its mitochondrial genes, meaning it can survive entirely without oxygen. For the future, the researchers state their discovery will benefit the field of evolutionary biological research for decades to come.
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