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. An international team of researchers has found a multicellular animal with no mitochondrial DNA, making it the only known animal to exist without the need to breathe oxygen. In their paper published in Proceedings of the National Academy of Sciences , the group describes their study of Henneguya salminicola, a microscopic, parasitic member of the group Myxozoa and its unique physiology.
Using deep sequencing approaches supported by microscopic observations, the group presented evidence that the 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. One of the common characteristics of all multicellular animals on Earth is mitochondrial respiration – the process by which oxygen is used to generate adenosine triphosphate (ATP) – the fuel used to power cellular processes. The process takes place in mitochondria, which has both its genome and the main genome found in the rest of the body’s cells. But now, there is a known exception: Henneguya salminicola. The researchers did not find any other mechanism for producing the fuel cells in H. salminicola would need to survive, but suggest they likely steal energy from their host using some type of proteins.
H. salminicola is a jellyfish-like microscopic parasite lives within the stomach of a salmon but it is not harmful to the fish and can stay with it for its entire life cycle. The parasite spends its life clinging to the inside of North Pacific salmon in a low to zero-oxygen environment. So, H. salminicola isn’t a new species, it belongs to the same family as corals and jellyfish; however, its genome has only just been mapped .
Florescence micrograph of spores
After the genome was sequenced it was studied under a fluorescence microscope in an attempt to better understand how it lives with no oxygen. This tagged various genes within the genome and that is how they found it had no mitochondrial DNA or even the genes to produce it. This isn’t the first creature discovered that can go extended periods without oxygen – but is the first complex organism that doesn’t require it at all.
Hence, H. salminicola provides an opportunity for understanding the evolutionary transition from an aerobic to an exclusive ‘anaerobic metabolism.’ Other simpler species like certain single-cell microbes can survive without oxygen via anaerobic metabolic mechanisms – but this is the first form of complex life. Species that have adapted to anaerobic processes did so to survive in low-oxygen environments and replaced mitochondrial systems with anaerobic ones .
The Researchers believe H. salminicola may have once had mitochondrial DNA but devolved from a more advanced free living jellyfish ancestor over millions of years. It has lost most of the original jellyfish genome but retained some complex structures – including stinging cells that it uses to cling on to the salmon.
1. Yahalomi D, Atkinson SD, Neuhof M, Chang ES, Philippe H, Cartwright P, Bartholomew J L, Huchon D, et al. A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome. PNAS February 24, 2020 https://doi.org/10.1073/pnas.1909907117
2. Yirka B. Henneguya salminicola: Microscopic parasite has no mitochondrial DNA. Phys.org. Feb 25, 2020. [https://tinyurl.com/sxazpk9]
3. Morrison R. Jellyfish-like parasite that lives inside North Pacific salmon is the ‘first ever animal that can survive without oxygen’ – and it sheds light on how alien life could exist on other planets. Mail One, Feb 25, 2020. [https://tinyurl.com/snnfajo]
Dr. Sanjoy Kumar Pal is a Professor of Biology in Skyline University Nigeria. He has a PhD. in Animal Genetics from Indian Veterinary Research Institute, India.