Weizmann Institute scientists have revealed the defense mechanisms of the most resistant creature in the world to radioactive radiation
The "Lord of the Rings" is the bacterium Deinococcus radiodorans (pictured), which is the most resistant creature on earth against radioactive radiation. The unusual resistance of the bacterium is mainly due to the fact that it organizes its genetic material in the form of a ring. This is according to a study by Prof. Avraham Minsky from the Department of Organic Chemistry at the Weizmann Institute of Science. The research findings are published today in the prestigious scientific journal "Science".
The microscopic "Lord of the Rings" is able to last and survive even when it absorbs radiation with an intensity of 1.5 million rad - a thousand times the intensity of radiation that any other living creature on Earth can withstand, and 3,000 times the intensity of radiation that humans are able to withstand. More than that: it turns out that he is capable of digesting radioactive materials, in a way that makes him an effective worker in cleaning up sites of radioactive waste. And if all this is not enough, it turns out that it is particularly resistant even in extreme conditions of dryness and cold, a feature that makes this bacterium one of the few creatures capable of living in the North Pole. The strange durability of the microscopic "Lord of the Rings" has been at the center of arguments in recent years between the scientists of the American space agency, NASA, and Russian scientists who claim that the "Lord of the Rings" came to Earth from Mars, where the level of radioactive radiation is higher compared to the background radiation of the Earth. Country.
This long-standing mystery was recently resolved, when Prof. Avraham Minsky from the Department of Organic Chemistry at the Weizmann Institute of Science found that the DNA of the resistant bacterium is densely packed in the form of a ring, which gives the bacterium its resistance to external factors (such as radioactive radiation) that harm in the genetic material and break its chemical sequence.
Radiation that damages the genetic material may interrupt both strands of the DNA molecule. Living cells, that is, both bacteria and cells in the human body, are able to repair only a few damages in their DNA. Other bacteria, for example, are able to repair only three to five DNA damages, while Deinococcus radiodurans is able to repair more than two hundred such damages. The excellent - and enviable - repair ability of this bacterium has previously led to the raising of a hypothesis that this surprising bacterium activates particularly effective repair enzymes. But a series of experiments showed that its repair enzymes are very similar to those that exist and work in other bacteria.
Using a variety of optical and electron microscopic methods, the members of Prof. Minsky's research group found that the DNA of Deinococcus radiodorans is arranged in a ring that does not allow broken pieces of DNA to disperse in the intracellular fluid and get lost, as happens in other creatures, including humans. In other words, the tiny "Lord of the Rings" does not lose genetic material, and does not allow parts of it to disperse. Even when his genetic material is broken into tiny segments as a result of powerful radiation, he makes sure to keep all the segments in their fixed places, in the structure of a dense and tight ring. After that, the repair enzymes go over the ring, "solder" the genetic segments to each other and restore the situation to repair.
"We believed that the key to the mystery could not be in the hands of the repair enzymes, which are also damaged by the radiation. Therefore, we began to look for the source of resistance in other properties of the bacterium, until we understood the true meaning of the arrangement of the genetic material in the dense ring", says Prof. Minsky.
In follow-up studies, the scientists found that the DNA repair process of the "Lord of the Rings" is conducted in two stages. In the first stage the DNA undergoes repair processes within the ring, but then it performs an even more surprising stunt. Deinococcus radiodorans is a single-celled creature divided into four separate "chambers". Each room contains a copy of its own DNA. Prof. Minsky's research group found two tiny passageways connecting the four rooms. Careful monitoring of the repair process revealed that after about an hour and a half of repair inside the ring, the second stage of the repair begins: the DNA is released from the structure of the ring and migrates to the next room, where it unites with the DNA copy residing there. At this point, the "normal" repair mechanisms, which exist in humans and other creatures, begin to operate: repair enzymes compare the two copies of the genetic material, using each of them as a backup for the missing information in the other. Since the DNA has already undergone the first stage of repair, during which many fragments were repaired, the second stage is carried out relatively easily.
The finding of the dense ring packing caused great puzzlement in Prof. Minsky's group: how is any creature able to function when its genetic material is packed in such a tight package? To perform their primary function, the DNA strands must unwind and allow the formation of messenger RNA which is the first step on the way to protein production. But how can they come undone when they are packed so tightly that they are almost unable to move? This question led to the discovery of another survival technique of the bacterium: out of the four copies of the DNA found in each such bacterium, there are always two or three found in a ring structure while the others are free to move. Thus, at any given moment there are DNA copies that can express themselves and create proteins, while other copies are packed in the tight ring, which is inactive, but gives the bacteria its miraculous resistance.
Prof. Minsky and other scientists believe that the unique features of the "Lord of the Rings", which give it its ability to withstand and survive, developed on Earth as a result of the harsh environment in which it developed, in extremely dry areas, where almost no other form of life exists. In other words, the mechanism that developed to give the bacterium the ability to withstand extreme dry conditions also gave it the ability to survive in conditions of strong radiation.
Understanding the way in which the organization of the genetic material in a tight ring provides resistance to harsh conditions, may help in understanding mechanisms to protect the genetic material in other systems, such as human sperm cells and spores of various bacteria - whose DNA is also organized in the form of a ring. And yet, unfortunately, the findings should not be expected to lead to the protection of humans against radioactive radiation. "Our genetic material is fundamentally organized in a different way" says Prof. Minsky.
