New Eukaryotic Endosymbiont Found

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In summary, a ciliate living in an anaerobic environment at the bottom of a lake has been found to have two endosymbionts - a hydrogenosome derived from a mitochondrion, and a newly discovered denitrifying endosymbiont. The latter uses a less efficient fermentation process to generate ATP and has a reduced genome compared to other bacteria. This second endosymbiotic event is similar to the development of chloroplasts in plant cells and highlights the significance of endosymbiosis in eukaryotic cell evolution.
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An anaerobic ciliate (a eukaryotic single cell organism) has been found with a non-mitochondrial derived endosymbiont that convert nitrate to nitrogen and produce ATP.
A ciliate containing a new endosymbiont has been found in a anaerobic (no oxygen) environment at the bottom of a lake, with high nitrate levels.
Nature news and views article here.
Nature research article here.

The ciliate is a eukaryote and would normally have inherited a mitochondrial endosymbiont. However, it lives in an anaerobic (oxygen free) environment and its mitochondrial endosymbiont has evolved (devolved) into a hydrogenosome (something that has happened, independently, more than once in other anaerobic ciliates). Hydrosomes use the less efficient fermentation set of reactions to generate ATP.
In this case, the ciliate was able to form an additional endosymbiotic relationship with a free living gammaproteobacterium that instead of using oxygen as an electron acceptor in it electron transport chain (ETC, like in mitochondria), it uses its ETC to make nitrogen from nitrate and produce ATP (denitrification).

Screen Shot 2021-03-03 at 7.28.00 PM.png


So, this ciliate has two kinds of endosymbionts, the hydrogenosome (degeneratively derived from a mitochondrion), as well as the ciliate's newly discovered denitrifying endosymbiont.

The denitrifying endosymbiont has a reduced genome of about 310 protein encoding genes, indicative of its status as an endosymbiont, but not as extreme a reduction as is found in the mitochondria (30-40 genes). E.coli bacteria for example, have about 4,000 genes. By living in the internal environment of another cell, the endosymbiont can take advantage of host cell's physiology and afford to lose redundant genes. However, it has not had as much evolutionary history in this environment as the mitochondria has had, so it has not been under these selective pressures as long.
Screen Shot 2021-03-03 at 7.34.56 PM.png


This second endosymbiotic event in this ciliate's evolutionary lineage, is similar to the eukaryotic cell precursors of plant cells, acquiring a second endosymbiont in the chloroplasts of today's plant cells.
 
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This discovery further underscores the importance of endosymbiosis in eukaryotic cell development and evolution.
 

1. What is a eukaryotic endosymbiont?

A eukaryotic endosymbiont is a type of organism that lives inside the cells of another organism. This relationship is known as endosymbiosis and is a form of symbiosis, where both organisms benefit from the interaction.

2. How was this new eukaryotic endosymbiont discovered?

This new eukaryotic endosymbiont was discovered through extensive research and analysis of genetic data from various organisms. Scientists were able to identify unique genetic sequences that were not found in any known species, leading to the discovery of this new endosymbiont.

3. What makes this new eukaryotic endosymbiont unique?

This new eukaryotic endosymbiont is unique because it possesses a combination of genetic traits from different organisms, making it a hybrid species. It also has a specialized role in its host organism, providing unique benefits and possibly playing a crucial role in its survival.

4. What implications does this discovery have for our understanding of evolution?

This discovery has significant implications for our understanding of evolution. It provides evidence for the theory of endosymbiosis, which suggests that complex organisms evolved from simpler ones through a process of symbiosis. It also highlights the potential for organisms to exchange genetic material and form new species through hybridization.

5. How might this new eukaryotic endosymbiont impact future research?

This new eukaryotic endosymbiont has the potential to impact future research in various fields, including evolutionary biology, genetics, and microbiology. It opens up new avenues for studying the mechanisms of endosymbiosis and the role of hybridization in the evolution of complex organisms. It may also have practical applications in fields such as biotechnology and medicine.

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