When we think of the word ‘animal,’ the first thought that comes to mind is a multicellular organism that requires oxygen to survive. However, as astonishing as it may appear, scientists have finally discovered an animal that can survive without oxygen. Recently, scientists have reported a multicellular parasite that lacks a mitochondrial genome which indicates that this organism does not breathe and has no oxygen dependency, unlike other multicellular species. Such a discovery, i.e., the absence of mitochondrial genome in a multicellular organism, is unprecedented and opens up a new avenue to investigate and understand the evolutionary process.
Scientists have always been intrigued by the origins of life. They traced back respiration, an essential life process, to sometime over a billion years ago. A symbiotic relationship was established when a large archaeon engulfed a bacterium. Over time, this new organism evolved and, eventually, the bacteria that ensconced within the archaea developed into a mitochondria organelle. Every cell (except red blood cells) contains mitochondria that are associated with the process of respiration and, thereby, in the production of a molecule called adenosine triphosphate (ATP). Mitochondrial respiration is regarded as an ancient characteristic of eukaryotic cells.
Stephen Atkinson, a senior research associate at Oregon State University’s Department of Microbiology, explained that Henneguya salminicola, a less than 10-celled organism, is a myxozoan cnidarian and is a common salmon parasite. This parasite belongs to the same phylum of jellyfish, anemones, and coral. They live inside salmon as a cyst and are not harmful in nature. H. salminicola is believed to have adapted to survive within the fish (host) that is mostly devoid of oxygen by plummeting its mitochondria genome entirely. Atkinson explained that the parasite loses the mitochondrial genome to save energy. It does not have to do extra work, such as to copy genes for various non-essential functions.
Scientists have studied H. salminicola, with the help of deep sequencing and fluorescence microscopy and found the absence of mitochondrial genome and lack of nuclear genes associated with transcribing and replicating mitochondria. As a control setup, a similar study was conducted on a closely related cnidarian fish parasite, namely, Myxobolus squamalis. The control group revealed the presence of a mitochondrial genome. This further confirms that H. salminicola does not require oxygen to survive. The exact survival mechanism is still unknown; however, it is possible that they extract ATP from the host.
Researchers are extremely excited about their findings and have said that their groundbreaking discovery provides an opportunity to understand the evolutionary switch from aerobic to exclusively anaerobic metabolism. They also claim that their research reveals that aerobic respiration, one of the most important metabolic pathways is not universal.
Atkinson and his team think that many more such species can be deemed as oxygen-free animals. In the future, they expect to discover many more species that may have unusual modes of existence.