American biologists have unlocked one of the secrets of hearts killer with the help of which people struggle with agricultural pests. They understood how they activate their "biological weapons" lethal to insects, bacteria, living in their intestines. Now people will be able to use this weapon, not resorting to services of the worms themselves.

Known to many specialists in plant protection from harmful insects (but, alas, not the General public) interest roundworms Heterorhabditis bacteriophora have unique "profession" in the animal world. They are not just "killer"and experts on the application of biological weapons. It is possible that these nematodes were the first living beings on Earth who "guessed" such a method of killing the victim (however, may actually those were their close relatives from sort Steinernema, which you can read" here).

The life of heterorhabditis simple and straightforward - the young larva in the intestines which are thousands of bacteria of the genus Photorhabdus luminescens (named for the ability to light up) and sits quietly in the ground and waiting for an insect larva. As soon as she come up to her closely, nematode enters the body of the victim through spiracles, anal hole or crack in the skin. Once inside, predatory worm dumps "sheepskin" and becomes an insidious killer.

Heterorhabditis releases from your intestines (mainly through the anus), the bacteria begin to multiply rapidly, not forgetting to synthesize substances Tc and Mcf. These organic toxins quickly kill the insect (which fails to defend against them), however, the nematode is not harmful. The same, realizing that "client" already dead, begins to feed liquid gruel, which are transformed under the action of toxins internal organs of the victim.

So, slurping nutrient broth, larva in passing turns to the adult form, finds "significant other", who settled in the same insect, mate, and lay eggs and with a sense of accomplishment departs for the other world. When the young hatch from eggs, from an unfortunate victim remains only inedible chitin, and they understand what to do here there's nothing left get out. But before that, each new larva swallows a number of bacteria - it is impossible to travel unarmed!

For a long time scientists investigating the life of heterorhabditis, could not understand why living in intestinal nematodes bacteria do not produce their dangerous substances, and once "free", immediately begin to poison all around. It was known that cells Photorhabdus inside worm are in an active stage - they rapidly multiply. However behave quietly and not trying to kill anyone. How is the transformation of the peace of symbiont in the dangerous killer?

And recently, a group of biologists from the University of California at San Diego and Yelisovo University (USA) finally found out how it works. The authors drew attention to the fact that Photorhabdus luminescens can form two forms. The first of them is called P-form, and the second - M-form (from the words of pathogenic and mutualistic). And all such names were given not for beautiful eyes.

It turned out that only cells M-forms can attach to the intestinal wall of the worm to penetrate into his cell, and then in the lumen of digestive tract larvae. However, the cells that form smaller, they breed slowly and toxic substances unable to produce. So the only thing they do is to live peacefully in the intestines of heterorhabditis, be fruitful and multiply.

However, before the larva will be ready to go hunting for insects, these peaceful roommates become larger R-cells that multiply several times faster and poisons can develop. They are the issues larva by getting into his six-legged "dining room", they kill the victim, and that they swallow larvae of the next generation before to get out of the already eaten parents production.

But the cells of this aggressive form can not get into the intestines in order to survive times of famine. And all because they are not able to establish contact with the intestinal cells of the worm. Therefore, in order to survive, bacteria must again turn into peaceful M-form which is taken in the "barracks and patiently waiting for the next "alarm".

What is responsible for such a metamorphosis? Having studied the genome of bacteria, scientists have paid attention to an interesting site called madswitch (the name of which should be translated as "the regulator genes mad", and not as "psyched switch"). This stretch of DNA really regulates the activity of important genetic complex mad responsible for the synthesis of proteins that are able to contact with the intestinal cells of the worm.

Biologists have found that peaceful M-shape this control works, and information from gene mad constantly read. That is why these cells can easily penetrate the intestine nematodes. However, apparently, the activity data genes disturbs the work of other sections of DNA - that is why M-forms do not produce poisons, as well as antibiotics for the suppression of bacteria-competitors, as well as proteins Cips and other substances necessary for the larvae to normal growth in the dead insect. Yes and glow these cells are much weaker than their R-fellows. However, there is a silver lining - activity madswitch allows M-cells to be more resistant to many antibiotics.

As for the aggressive P-forms, they are madswitch is completely turned off. That is why they can't produce the proteins that are responsible for contact with the intestinal cells (because it is not the mad), but is capable of other interesting and useful things. And off this site through activities located next to him gene madR his protein and taking lots of activity "switch". Contrary to switch contributing to the emergence of the M-form? performs a sequence madO, which is located quite in another part of the same chromosome.

Scientists suggest that bacteria can somehow themselves to adjust the frequency of direct and inverse transformations, changing the level of activity areas madR and madO. However, it is unclear whether this occurs in nature. In laboratory conditions, metamorphosis occurred randomly - P-forms turned in M-fellows with a frequency of 1.21·10-3 on cell generation, and the frequency of inverse transformations was lower: only 4,30·10-5. But it is not excluded, that in the natural world all this is regulated in the old way is called natural selection.

In fact, in the cavity of the intestine worm before he decides that it is time to eat, and in the body of an insect, P-forms predominant, because multiply faster (that is, have a selective advantage over M-forms, replacing them). But to attach to the intestinal wall nematodes young worms can only M-forms, which are dominated by at these stages of the life cycle. However, just one the week after, bacteria gets into "barracks", M-shaped almost entirely replaced by P-forms. The result is a young heterorhabditis is "armed and dangerous", that is completely ready to the further hard work for the benefit of all mankind.

This case is interesting from the point of view of modern evolutionary view - at least because he is one of the exceptions to the General rule, according to which? acquired characteristics can not be inherited inherited only genome changes that occurred in germ cells). But P. luminescens really with enviable regularity in the process of life is changing gene, and these changes undoubtedly passed on to offspring. Formally, they can be called "evolutionary", because they are very similar to mutations (even if they are targeted and adjustable), which are supported by natural selection and help bacteria every time to adapt to the new environment. So in this case were right supporters Lamarck (admit such succession), not followers of Darwin (related skeptical).

From a practical point of view the work of American biologists valuable because now, when it became clear how to turn a peaceful bacteria in the biological weapon protection of plants you can do without nematodes. Just modify themselves P. luminescens so they gave only R-form, grow them in the lab (which is much easier than maintaining a culture of heterorhabditis) and spray suspension of their cells fields, gardens and kitchen gardens. So now people will be able, not resorting to services of the worm, to use its biological weapons...