https://tokyo3.org/forums/holiday/?main=https://tokyo3.org/forums/holiday/welcome/ Scientists Find The First-Ever Animal That Doesn't Need Oxygen to Survive MICHELLE STARR 25 FEB 2020 Some truths about the Universe and our experience in it seem immutable. The sky is up. Gravity sucks. Nothing can travel faster than light. Multicellular life needs oxygen to live. Except we might need to rethink that last one. Scientists have just discovered that a jellyfish-like parasite doesn't have a mitochondrial genome - the first multicellular organism known to have this absence. That means it doesn't breathe; in fact, it lives its life completely free of oxygen dependency. This discovery isn't just changing our understanding of how life can work here on Earth - it could also have implications for the search for extraterrestrial life. Life started to develop the ability to metabolise oxygen - that is, respirate - sometime over 1.45 billion years ago. A larger archaeon engulfed a smaller bacterium, and somehow the bacterium's new home was beneficial to both parties, and the two stayed together. That symbiotic relationship resulted in the two organisms evolving together, and eventually those bacteria ensconced within became organelles called mitochondria. Every cell in your body except red blood cells has large numbers of mitochondria, and these are essential for the respiration process. They break down oxygen to produce a molecule called adenosine triphosphate, which multicellular organisms use to power cellular processes. more at link...... the paper: https://www.pnas.org/content/early/2020/02/18/1909907117 A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome: Significance: Mitochondrial respiration is an ancient characteristic of eukaryotes. However, it was lost independently in multiple eukaryotic lineages as part of adaptations to an anaerobic lifestyle. We show that a similar adaptation occurred in a member of the Myxozoa, a large group of microscopic parasitic animals that are closely related to jellyfish and hydroids. Using deep sequencing approaches supported by microscopic observations, we present evidence that an animal has lost its mitochondrial genome. The myxozoan cells retain structures deemed mitochondrion-related organelles, but have lost genes related to aerobic respiration and mitochondrial genome replication. Our discovery shows that aerobic respiration, one of the most important metabolic pathways, is not ubiquitous among animals. Abstract: Although aerobic respiration is a hallmark of eukaryotes, a few unicellular lineages, growing in hypoxic environments, have secondarily lost this ability. In the absence of oxygen, the mitochondria of these organisms have lost all or parts of their genomes and evolved into mitochondria-related organelles (MROs). There has been debate regarding the presence of MROs in animals. Using deep sequencing approaches, we discovered that a member of the Cnidaria, the myxozoan Henneguya salminicola, has no mitochondrial genome, and thus has lost the ability to perform aerobic cellular respiration. This indicates that these core eukaryotic features are not ubiquitous among animals. Our analyses suggest that H. salminicola lost not only its mitochondrial genome but also nearly all nuclear genes involved in transcription and replication of the mitochondrial genome. In contrast, we identified many genes that encode proteins involved in other mitochondrial pathways and determined that genes involved in aerobic respiration or mitochondrial DNA replication were either absent or present only as pseudogenes. As a control, we used the same sequencing and annotation methods to show that a closely related myxozoan, Myxobolus squamalis, has a mitochondrial genome. The molecular results are supported by fluorescence micrographs, which show the presence of mitochondrial DNA in M. squamalis, but not in H. salminicola. Our discovery confirms that adaptation to an anaerobic environment is not unique to single-celled eukaryotes, but has also evolved in a multicellular, parasitic animal. Hence, H. salminicola provides an opportunity for understanding the evolutionary transition from an aerobic to an exclusive anaerobic metabolism.
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