Henneguya salminicola: Jelly-Like Parasite That Does Not Need Oxygen To Breathe

For the very first time, a type of multicellular organism was found to survive without depending on oxygen, changing the definition of what an animal is.

Oxygen Metabolism

Experts believe that more than 1.45 billion years ago, life began to develop the ability to metabolize oxygen or respirate. A theory suggests that a microorganism called archaeon engulfed a smaller bacterium whose new home became beneficial to both parties, allowing them to stay together.

The symbiotic relationship led to the evolution of both organisms, where the bacteria settled to become organelles known as mitochondria. Today, every cell in our body, except the red blood cells, contains large numbers of mitochondria, which play an important role in the respiration process.

Mitochondria works by breaking down oxygen to produce a molecule called adenosine triphosphate. This molecule is used by multicellular organisms to power cellular processes.

Some adaptations, however, enable some organisms to survive in low-oxygen (hypoxic) environments. There are single-celled organisms that have evolved mitochondria-related organelles to carry out anaerobic metabolism. Still, the possibility of exclusively anaerobic multicellular organisms has been the subject of many scientific arguments.

Oxygen-Free Survival

In 2020, a team of scientists discovered a jellyfish-like parasite that does not possess a mitochondrial genome, the first multicellular organism ever found with such an absence. Their findings were discussed in the paper "A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome."

Led by Dayana Yahalomi of Tel Aviv University, a team of researchers investigated a common salmon parasite called Henneguya salminicola. It is a cnidarian with the same phylum as jellyfish, corals, and anemones. It is known for creating cysts in the flesh of fish and living with the salmon for its entire life cycle.

Henneguya salminicola has the ability to survive hypoxic conditions. However, exactly how it does so can only be answered by looking at its DNA.

The team used deep sequencing and fluorescence microscopy to study Henneguya salminicola. They found that this organism had lost its mitochondrial genome and its capacity for aerobic respiration.

It also lacks almost all the nuclear genes involved in the transcription and replication of mitochondria. Henneguya salminicola had evolved mitochondria-related organelles, although these are unusual. They were found to have folds in the inner membrane, which were not typically seen in other single-celled organisms.

The lack of a mitochondrial genome means that this organism does not breathe. As a matter of fact, it lives its life entirely free of oxygen dependency.

Henneguya salminicola remains a mysterious creature whose loss of mitochondrial genome is consistent with an overall trend in its family. Over millions of years, they devolved from a free-living ancestor of jellyfish into a simpler parasite we encounter today.

According to researchers, their discovery confirms the theory that adaptation to an anaerobic environment is not exclusive to single-celled eukaryotes. In fact, it has also evolved into a multicellular, parasitic animal.

The discovery of Henneguya salminicola not only changes our understanding of how life can actually work here on our planet, but It also offers insights into the evolutionary transition from an aerobic to an exclusive anaerobic metabolism. Moreover, it can also have implications for the search for extraterrestrial life.