A single one against all rules

All single cells have an area in which energy generation takes place. Really all? No. An unruly little witch will not stick to this rule and question biological certainties. And also this cell is good for some surprises.

Most single cells, like these diatoms, have "power cells" for energy generation. But there are exceptions.

Most of us know mitochondria from biology lessons as the "power stations" of the cell. They are responsible for energy production and are vital for people, animals and plants. In the unicellular eukaryotes, mitochondria, together with the nucleus, belong to the basic equipment. This has been thought at least so far, because researchers from the Charles University in Prague have discovered a single organism who does not want to stick to this rule and question our biological general education.

At first glance, eukaryotic single-cells are not exactly one of the most spectacular creatures. If you look at the few micrometer-sized organisms under the microscope, you will see a few round cells, some of which can still move on the outer membrane with the help of thin threads. But when Anna Karnkowska speaks of the monks and their evolution, she gets into a rave:

"These cells are really interesting, especially their genomes, some of which are built in a bizarre way, which is absolutely fantastic, and the diversity is much bigger than we've ever thought."

Where and how is the energy produced by the cell?

Typical for eukaryotes is that they have a nucleus in their DNA. This distinguishes it from prokaryotes, which include, for example, bacteria: in which the hereditary information floats freely in the cell. A further characteristic of eukaryotes are the mitochondria, areas separated by a membrane in the cell, in which, among other things, the energy production takes place. When Anna Karnkowska and her colleagues at the Charles University in Prague examine a single cell for the first time, the mitochondria are an important aid. For they reveal a lot about the way of life of every kind and help to classify them into the tribal tree of the eukaryotes. This is the case with the unknown solitary, which later was called Monocercomonoides. Anna Karnkowa:

"He had been isolated from the stomach of a chinchilla eight years previously, although similar organisms were already known, but ultimately Monocercomonoides did not really agree with any one, it was only clear that it was an anaerobic organism, The environment. "

What immediately became apparent: Genuine mitochondria, which can be recognized under the microscope as folded structures in the cell, did not have Monocercomonoides. This is not unusual for organisms living in an anaerobic environment such as the digestive tract of an animal. Anna Karnkowa explains:

"Anaerobic organisms often have altered mitochondria, developed from the original mitochondria, and work a bit differently." While our mitochondria require oxygen for many reactions, these variants come out without oxygen and produce their energy in a different way.

Detective work: mitochondria, desperately sought

These alternative, chemical reactions are not only independent of oxygen, but can also proceed directly in the cytoplasm of the cell. A separated reaction chamber is superfluous. The mitochondria of anaerobic organisms have therefore often shrunk to so-called mitosomes. These may be so small that they are difficult to detect even under high magnification under an electron microscope. Anna Karnkowska therefore looked at the genotype of Monocercomonoides to look for them.

"We have studied the entire genome according to the building instructions for mitochondrial proteins, both those still being used and inactive remains." The footprints of mitochondria in the genome, so to speak. "

Anna Karnkowska also looked for proteins that have nothing to do with energy production. Specific proteins from the membrane of the mitochondria for example. But none of them could prove it.

"This has surprised us, although it has already been known that there are greatly reduced forms of mitochondria, and that they can theoretically be entirely absent, but the results of research over the past twenty or thirty years have tended to suggest that Some form of mitochondria or mitosomes is present. "

The last possibility to find mitochondria was the search for iron-sulfur cluster scaffold proteins, for short, ISCs for Anna Karnkowska. These proteins are necessary for another process in the mitochondria, which is also vital to the cell: the formation of complexes of iron and sulfur without which certain enzymes do not work.

"All mitochondria have this function, but even the most reduced ones that have lost all other functions must still fulfill this function, and when they turn off artificially, the cells die, so we searched for the corresponding proteins, but we could not Instead, we have found components of another complex that are otherwise only bacteria. "

Highly adaptable single cell

Thus, monocercomonoides no longer has its original ISC proteins, but instead uses a different system with similar function that functions in the cytoplasm. Anna Karnkowska assumes that Monocercomonoides first took over the foreign system of bacteria and thus could do without his own system. In the course of evolution, the mitochondria were also lost, since they were superfluous. For Anna Karnkowska a find, which makes her enthusiasm for solitary ones even bigger.

"This shows what unique organisms have evolved and how large the evolutionary diversity is in single cells, which are so flexible that even the mitochondria could be completely lost, which is one of the most extreme examples of the enormous adaptability of the cell. But if all the corresponding functions are fulfilled differently, even that is possible.