Our planet is inhabited by a huge number of different complex organisms. Yet we can guide the dividing line between them. On the one hand, “microbes” will remain with a small, simply-built cell–bacteria and non-related, but similar archea. On the other hand, the Division will thicken all the animals, plants and fungi, as well as their unicellular relatives falling between the primes and algae.
All these organisms can boast of a complex cell containing the nucleus, and it is clear that the microbes, who dominated the earth billions of years before anyone else, had to develop gradually.
Secrets of Loki Castle
The issue of the origins of more complex cells and the complex organisms do not give scientists sleep. The important step on this journey was nine years ago when the team of European researchers managed to remove deposits from the vicinity of the deep-sea hot water pump called Loki Castle.
Over the next few years, these deposits have been shown to contain new, not yet described, microbes, one of which showed greater genetic affinity to more complex organisms than all the previously known lines of bacteria and archeologists.
However, research purely on the basis of genetic data has limits. For example, we can never be certain whether the genetic information extracted from the environment belongs to another evolutionary line. Likewise, based on genetic data, we can only indirectly conclude on the functioning, behavior, and appearance of the organisms studied.
Almost ten years after the whole story began, the Japanese team announced that he had managed to develop the appropriate microbe in the laboratory. They are so special that they will almost certainly force us to rewrite theories about the emergence of more complex cells.
Three domains of Earthlife
The cells of multicellular animals, plants, fungi, and their unicellular relatives are characterized in addition to a large size mainly by the presence of nuclei, various membrane structures, supportive protein scaffolding and several types of cellular organs or organ.
Among Organelami are the most interesting and from an evolutionary point of view the most important mitochondria. Sometimes called “cellular power plants”.
The mitochondria were originally separate organisms, the oxygen-breathing bacteria that came into the cells of our ancestors and established a mutually beneficial symbiotic relationship with them. Based on the study of genetic information, we know that these ancestors were organisms from the vicinity of today’s archeology.
The birth of the first more complex, technically speaking eukaryotic cells can thus be described as a combination of two simpler, prokaryotic, cells in a higher-order organism.
Thanks to an alliance with oxygen-based bacteria, the first eukaryotic cells have acquired a rich energy source, allowing them to allow the exact division of their cells, the creation of large panoplies (organs used for movement), or the absorption of foreign organisms. But it is not clear how the association of the archeology with the bacteria occurred.
According to one group of theories, the ancestor of the mitochondria got into the archaeological cell as a piece of food or parasite and there he managed to survive. According to other concepts, the symbiote protected the archaeological cells from the toxic influences of oxygen, or in their relationship from the beginning, some other form of free cooperation was played.
And this we missed the hypotheses, according to which the transformation of prokaryotic cells in eukaryotic was attended by other organisms, or other, even more, exotic concepts.
The only way to cut the mystery is that the finding of the closest living microbial relatives of eukaryotic organisms is likely to remain. Their ecological strategies and symbiotic relationships could tell how eukaryotic cells evolved from the prokaryotic cell.
By the arch we return to the line of the archeologist discovered nine years ago at the bottom of the Atlantic. She was named Lokiarcheota after her discovery, the hot vacuum pump Lokiho castle, and its “Nordic” position near Iceland. Over the coming years, scientists have described a number of related lines, so today they are talking about the whole group of eukaryotic relatives of the archivists named after the headquarters of the Nordic gods Asgard.
The stumbling block, however, is that we have only a piece of information about these lines, based on the reading of the genetic material taken from the sea deposits. In other words, until recently, we had no idea how these organisms look and what they follow in their environment relationships. But this is changing now. A group of Japanese scientists announced that they had managed to grow the Archea from the Lokiarcheota group in a laboratory.
Scientists have shown in the manuscript, which is waiting in the bioRxiv archive for publication by a specialist magazine, that the whole project has been occupied for almost twelve years. If you wonder how research could take longer than time has elapsed since the discovery of the group studied, the answer is brainless. The project, which eventually succeeded in cultivating the culture of Lokiarcheot, began completely independently.
The Japanese tried to imitate the conditions of the underwater vacuum pumps of hot water saturated with methane in the Nankai sea drop so that they could grow and explore the local organisms in the laboratory. Until later, the organisms in the apparatus were also detected by Lokiarcheota. But their representatives soon proved to be an almost superhuman task.
The Lokiarcheota, in contrast to the microbes, who willingly grow on the agar plates, exhibit extremely low propagation rates. In contrast to the standard few hours, 30 to 60 days were only acclimatized and the next three months slowly accelerated multiplication.
Even under the ideal conditions at which antibiotic researchers have been killing competing bacteria, Lokiarcheota has not reached a higher cutting speed than every two to three weeks. The cultivation of the trunk to the concentrations usable in experimental research was first in the apparatus and then in the insulated flask with the nutrient medium, it took several years.
The strangest microbes
The cultivated tribe of Lokiarcheot got the name Prometheoarchaeum syntrophicum. They are small globular cells without prominent organelles seeking oxygen-free environments. However, they are surprisingly complex in shape terms. They create long, often branched, sprout and blistering chains. They also secrete sticky polysaccharide mass.
Prometheoarchaeum can boast a wide range of genes influencing the functioning of membranes and the formation of vesicles or cellular support scaffolds, which we otherwise find only in eukaryotes. Isolating (except for symbiots) The pure culture of its cells has helped to disprove the doubts as to whether these genes were not blended between the material previously removed from the environment.
From an evolutionary point of view, it is uninteresting that Prometheoarchaeum needs a symbiotic partner – either Halodesulfovibrio or Archea Methanogenium. These assistants are demonstrably supplying hydrogen and the remnants of formic acid, which is obtained by decomposition of amino acids.
In return, the archaeological organism receives various important organic substances, which it alone cannot create.
From genetic data, we know that various representatives of the Asgard group are metabolically very versatile and use the pleiade of other methods of metabolic transformation. The decomposition of amino acids, however, is likely to be the original method by which they obtained their ancestors.
Based on these discoveries, Japanese researchers formulated a new theory of how eukaryotic cells could develop. In the beginning, they were faced with a similar symbiotic relationship that we observed at Prometheoarchea. Along with the oxygenation of the planet, however, the paths of today’s lokiarcheot and ancestors of eukaryotes broke up.
The archaeological ancestors of the eukaryotes were moved to the boundary between the oxygenated and oxygen-free environment – which was the most nutrient. In the same layers, our ancestors began to threaten toxic oxygen. The solution to this problem was the establishment of another symbiotic relationship, this time with the bacterial ancestors of mitochondria.
Greater efficiency was achieved by this cooperation in at least semi-closed environments defined by cellular growths. These could grow, so the ancestors of the mitochondria remained closed inside the archaeological cells.
Thus, the ancestors of eukaryotes could engage symbiots in their own body even without the energy-intensive absorption of material used by today’s protos. Gradually developing mitochondria took over the functions of other symbionts and followed the development of other eukaryotic properties.
Whether Eukaryotes originated in this way will show up further studies. On the basis of new data, however, it seems increasingly likely that symbiotic relationships have played an important role in the emergence of more complex cells than accidental survival of the infected bacteria.
Japanese researchers also cultivate other lines from the Asgard group and several other uncultivated microbial organisms. Other surprises may not let them wait long.
Source: Imachi H, Nobu MK, Nakahara N, … & Matsui Y (2019): Isolation of the archaeon at the prokaryote-eukaryote interface. bioRxiv, online.