Researchers say this finding challenges everything we know about life on Earth and what it needs.
The history of the Earth goes back more than 4.5 billion years. Life began to evolve the ability to absorb oxygen, that is, to breathe, more than 1.45 billion years ago: a larger archaeon absorbed a smaller bacterium, and somehow this union turned out to be beneficial to both are, writes Science alert.
This symbiotic relationship then led to the two organisms evolving together. Eventually, the bacteria that settled inside became organelles known as mitochondria. In fact, every cell in our body, with the exception of red blood cells, contains a large number of mitochondria, which we need for respiration. It is the mitochondria that break down oxygen to produce the molecule adenosine triphosphate, which multicellular organisms use to power cellular processes.
It is known that some organisms have evolved to adapt to living in conditions of low oxygen or hypoxia. Scientists have discovered that some single-celled organisms have developed organelles associated with mitochondria for anaerobic metabolism; but the possibility of the existence of exclusively anaerobic multicellular organisms has been the subject of some scientific debate.
That was until a team led by Dayana Yahalomi of Tel Aviv University took a look at a common salmon parasite, Henneguya salminicola. It is known to belong to the same phylum as corals, jellyfish and anemones. The cysts that the parasite forms in fish flesh are unsightly, but during their entire life cycle these parasites do not pose a threat.
The results show that by hiding in its host, the small cnidarin can survive hypoxic conditions. But until now, scientists did not understand how he managed to do this. During the study, the team examined the parasite’s DNA.
The scientists used sequencing and fluorescence microscopy, which allowed them to closely study the parasite. The team discovered that the cnidarin had actually lost its mitochondrial genome. He also lacked the ability for aerobic respiration and almost all nuclear genes involved in mitochondrial transcription and replication.
Like single-celled organisms, the parasite developed organelles associated with mitochondria, but they were not ordinary organelles: their inner membrane has folds that are usually not visible. Note that for comparison, the team used the same sequencing techniques and microscopy on the closely related cnidarian parasite Myxobolusquamalis, which was used as a control and clearly showed a mitochondrial genome.
Thus, scientists confirmed that there really is an organism on the planet that does not need oxygen at all to survive. Scientists still don’t know exactly how this happened, but they plan to shed light on the mystery of how the parasites managed to distance themselves from their free-living jellyfish ancestors and turn into a much simpler parasite.
The organism is known to have lost most of the original jellyfish genome, but strangely retains a complex structure reminiscent of the stinging cells of a jellyfish. It is known that the parasite does not use them to sting, but to cling to the host.
The study authors believe that their results will further enable them to develop strategies that help protect fish from parasites.
