Defining what life is much more difficult than it seems. Since antiquity, legions of scientists and philosophers have looked into the question, with various and varied conclusions – and even today, there is no solid consensus. The debate may even be more complicated, following the discovery of a new small structure with singular properties.
This work was carried out by the Ryo Harada team, a specialist in the genomic affiliated at the University of Dalhousie. Originally, these researchers were in the process of making an inventory of DNA of Citharist Royala kind of plankton, and multiple symbiotic bacteria which intervene in its life cycle. However, during this routine investigation, they came across a small suspect DNA loop which quickly caught their attention: it points to the Presence of another entity which, at first glance, seems to enter any of the main known biological categories.
An entity between cells and viruses
Phylogenetically speaking, this entity called Candidate Sukunaarchaeum amazing seems to belong to the group of archaea. This term designates very varied unicellular microorganisms which form a distinct area of bacteria and eukaryotic organisms-those with an organized nucleus, such as plants, animals or fungi. But the reality is more nuanced, because this entity has a particularly strange dichotomy.
On the one hand, she recalls a lot of viruses because of her lifestyle. Like these, Sukunaarchaeum Adopt a parasitic approach: It does not have the metabolic machinery necessary to survive aloneand delegates the majority of its biological functions to its host. In fact, the majority of its genes are dedicated to a single function: replication, all of the biochemical processes which aim to produce new individuals. A point that strongly evokes the ultra-limited genomic strategy found in viruses.
« Its genome is deeply stripped, devoid of practically all recognizable metabolic pathways and mainly coding the machinery of its replication system “Explain Harada and his team in their article.
But the comparison stops there. Indeed, Sukunaarchaeum still has several genes associated with functions that do not exist in these parasitic entities. For example, we can cite ribosomeskey elements of cell machinery which make it possible to synthesize the proteins essential to life by decoding the information contained in the messenger RNA. Viruses are typically devoid of this; They exploit those of their host to complete their life cycle.
But the most important difference concerns the biological organization of this strange microorganism. It turns out that Sukunaarchaeum produces proteins that seem involved in the training of a membranea small organic capsule that protects internal machinery. This characteristic is traditionally associated with living cells, and it is a key difference compared to viruses that do not have this kind of membrane.
In the end, we end up with a entity that exists in a kind of organic gray areawith a typically cellular structure and functions, but a minimalist metabolism that is closer to viruses.
« Sukunaarchaeum could represent the cell entity closest to a viral existence strategy “Write the authors. “” This extreme specialization questions our fundamental understanding of the minimum requirements of cell life. »
Be or not to be … living, looking for a consensus
In other words, cand discovery blurs even more the definition of life. A fairly extreme statement, but perfectly justified in this specific case.
To re -situate the context, the philosophers of antiquity, like the essential Aristotle, generally defined life through a set of concepts such as movement, growth and reproduction. This definition was then clarified with the emergence of biology, and especially following the invention of the microscope. This revolutionary instrument allowedObserve the first cells – biological structures that have long been considered as The determining criterion of the living.
But this intuitive and very clean distinction was quickly called into question, in particular with the Discovery of the first viruses. The latter do not have a cellular structure per se and seem mainly inert – but they are still capable of reproducing, contain genetic material and are subject to the natural selection process.
So should we consider them as living beings, even if it means adapting the definition? Most modern biologists consider that not. But this question continues to be the subject of harsh debates in the scientific community; it does not exist Still no clear consensus Today. In this context, the discovery of a new organization with such ambiguous identity will probably only complicate this effort of categorization.
A promising study, but also to confirm
However, it is important to specify that this is a pre -publication study, which means that it has not yet passed the CAP of peer rereading – a critical process where other specialists assess the methodology and conclusions of their colleagues. The results must therefore be interpreted with caution.
But it is still a fascinating paper that reminds us of how blurred the borders in biology. These recurring difficulties in finding universal criteria to define life perfectly illustrate the fascinating complexity of our world, and show that even the most fundamental concepts remain open to interpretation – with all that that implies for the future of research.
The study text is available here.
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