Microscopic organism 450 million years old in the lakes of Greece

Putting together the pieces of a complex research puzzle that until now raised more questions than it answered, an interdisciplinary team of researchers from around the world, including Greece, confirmed the existence of one of the few organisms with a very large continuous presence on the Earth. It’s about the tiny ones euglenoidswith an evolutionary course at least 450 million years old.

Euglenoids are a group unicellular organisms, which belong to the category of protists, i.e. they are not classified either in animals or in plants. Until today, their existence was known, but scientists had not established one of their main functions: the creation of cysts around them, like a nest, whenever they felt threatened.

A consequence of this was that scientists were detecting fossilized cysts around the world, in excavations and in sediments from rivers, lakes and seas, with common characteristics, but they did not know what they were. They were associated in the literature with different types of plant seeds and even remains of algae.

In recent research, published in the journal Review of Palaeobotany and Palynology, a team of scientists from Netherlandsthe Hellasthe USAthe Britain and Australia unites, after an exciting search, many pieces of the same “puzzle” and sheds light on the microfossils that remained a mystery for many years.

The thread of this search began to unravel twelve years ago, when Bas van de Schootbrugge, then a researcher at Goethe University in Frankfurt and now at Utrecht University, and Paul Strother from Boston College who had visited the German university, were trying to interpret such 200-million-year-old cysts included in a microfossil record from drilling in northern Germany. They sought the advice of the Greek palaeoenvironmentalist at the University of Heidelberg, Andreas Koutsodendris, who has specialized knowledge of palynology (the study of pollen) and had studied similar but younger cysts of 200 years old from the Vouliagmeni lakes of Perachora and Aitoliko in Greece. Together with researcher Wilson Taylor from the University of Eau Claire in Wisconsin, the team made, with a specialized microscope, sections of fossil cysts just 20 micrometers in size, found in the two Greek lakes, to analyze their structure.

“We started studying these cysts and realized that we didn’t know either what organism it was or the environmental conditions it was in. We found out that there is literature that mentions the organization, but no one knows what it is, so they call it differently”, Andreas Koutsodendris recalls speaking to APE-MPE.

The team hypothesized that these cysts are part of the unicellular euglenoids, but then realized that only one publication in the world linked the cysts to this class of protists. The answer came from an amateur scientist in Australia, Fabian Weston. As a filmmaker, Weston primarily films and uploads his videos to his YouTube page (https://www.youtube.com/channel/UCShLhIReMWZSe1xZI2E2pWQ).

The scientific team found a video in which Fabian Weston placed under a microscope a drop of water taken from a lake in New South Wales and unknowingly filmed living euglenoids, which, stressed by being removed from the water, created around them cysts. These cysts looked very similar to cysts found throughout the fossil record, so their relationship was certain to the scientists. Unwittingly, the amateur scientist had filmed the first evidence of cyst formation by euglenoids and therefore their connection to the unknown fossils.

“By putting together all the pieces of the puzzle in the literature of the past, we realized and proved that this organism exists on Earth continuously and has been fossilized for the last 450 million years”, points out Andreas Koutsodendris.

In Greece, such cysts were found in many lakes and lagoons, but also in samples from the Aegean and the Ionian, i.e. in a marine environment.

They have also been found throughout the Mediterranean, even in archaeological excavations in Italy.

But where does this organism actually live? This was the next question the scientists had to answer. By piecing together all the available information, the research team created a distribution map and found that euglenoids are found in temperate and tropical climates and latitudes up to about 45 degrees. Also, they live in fresh water, especially in rivers or even in small lakes and when their environment dries up and they find themselves in a state of stress, they create cysts around them, which are transported from land even into the sea. When the environment becomes suitable again, the euglenoids emerge from the cyst and continue their lives. “So it is not the organism itself that fossilizes, but the cyst it made to protect itself and for this reason, while cysts are a very common finding in palynological studies, scientists did not know what they are,” Mr. Koutsodendris emphasizes to APE- BE.

He underlines how important information is extracted from the study of single-celled organisms and in particular from the finding that euglenoids have such a long time presence on Earth. “Through these organisms, biologists can understand the evolution of organisms and ultimately understand how life originates and evolves on Earth.”

In addition, the finding that euglenoids create cysts when stressed by drought gives scientists more tools to identify drought conditions in the regions where cyst fossils have been found. “Thus, we will be able to study the evolution of the climate over long periods of time in the past. And if we know the climate of the past, we can use the information to possibly predict the climate of the future”, concludes Mr. Koutsodendris.