Charles University)
Illustration of a cross section of a Solarion cell
It’s not every day that biologists announce an entirely new branch of life – and it’s been hidden under their noses for years.
Scientists were keeping in the laboratory a sample of marine ciliates that had been collected in Croatian waters in 2011. When, suddenly, these ciliates began to die, a new and tiny creaturewhich scientists named Solarion arienae.
The organism now discovered was featured in a publication last week in the journal Nature.
“This organism allows us to go back to a very ancient chapter of cellular evolution that, until now, we could only reconstruct indirectly“, explain protistologists Ivan Čepicka e Marek Valtfrom Charles University, in the Czech Republic, lead authors of the study.
“The cells of Solarion they are tiny and only slightly mobiles. We ignored them for years in ciliate culture… considering we didn’t detect Solarion even in our long-term laboratory culture, probably would go unnoticed in natural samples“, write the researchers.
The fascinating shape of this microorganism, similar to a small sun, is only rivaled by what it hides inside, notes the .
It is unicellular eukaryote it has a membrane-bound nucleus, full of DNA, just like each of our cells. And, like our cells, it has Mitochondria – the “powerhouse” of the cell, where fat and carbohydrate molecules are converted into chemical energy.
The team showed that the Solarion Does not fit into any of the categories existence of eukaryotes and, therefore, this small solitary “sun” now becomes share a newly defined phylum with another bizarre protist, Sporadic meteorwhich, in turn, is inserted into a kingdom also newly establishedwhich only includes protists, equally distant, Provora e Hemimastigophora.
But their mitochondria are clearly different of all that scientists had seen to date. They continue to retain genetic traces of what may once have been a completely autonomous being.
Scientists think that Mitochondria were once organisms in its own right – an ancient bacterium. But, at a certain point in the evolutionary history of life on Earth, they settled inside the unicellular body of another organism.
We know this because of the genetic code which is still stored today in all mitochondria, which all date back to the same ancestral phylum.
Over time, these two parts became so closely linked that the border between the “self” and the “other” became completely blurred. Inside most of our cells mitochondria continue to exist, with their own set (much abbreviated) of DNA, without which we wouldn’t be able to survive.
In most eukaryotes – animals, plants, fungi, algae and a multitude of unicellular companions – mitochondria retain few traces of its primordial independence.
But the Solarion still keeps in its microscopic body a genetic recall of that long-forgotten time: the secA genewhich was part of the “molecular kit” of the proto-mitochondria, involved in the transport of proteins across its membrane, when it lived independently.
This is excellent news for endosymbiotic theory of the origin of mitochondria. This is direct evidence of the life mitochondria led before they were fully integrated into the eukaryotic cell, giving us an unprecedented look at how the last common ancestors of eukaryotes related to each other before merging into one.
“O Solarion is a remarkable reminder of how we still know little about the diversity of microbial life”, emphasize Čepička and Valt.
“The discovery of a lineage so deeply rooted in evolution – essentially a living fossil – shows that fundamental parts of the history of eukaryotes remain hidden in areas we rarely explore“.
