Scientists have known for a long time that many types of bacteria form various communities, consisting of a huge number of individuals, and these "collectives" of microorganisms demonstrate rather curious and difficult to explain features in behavior. Colonial myxobacteria are the most striking example of such "originals".
These microorganisms feel most at ease in the soil, in manure, and also on decaying plant remains. However, their short rod-shaped cells, thousandths of a millimeter in size, can exist singly.
But still, most often they are organized into clusters of thousands, which, in search of food with their entire mass, move from one place to another. At the same time, each member of the team secretes abundant mucus, which serves as a kind of "lubricant", with the help of which armada of microorganisms slide over the soil surface.
It is surprising that all the cells of the colony act in surprisingly coordinated manner, as if they were being controlled by an invisible conductor. And if suddenly some bacterium is beyond the edge of the colony, it immediately rushes back, as if some invisible thread is forcing it to do so.
As soon as prey appears on the way of this host of microorganisms, for example, an accumulation of bacteria of another species, the vanguard of the colony turns sharply to the victim and crawls over it, covering it with many tiny bodies. After that, the time of a real feast begins for myxobacteria, during which, with the help of special enzymes, it digests the prey to an easily digestible state.
If the same species of myxobacteria find themselves in the water, they immediately transform into globular colonies consisting of hundreds of thousands or even millions of individuals. And when other microorganisms or their colonies come across on the way of this miniature ball, the active movements of the cells pull the victim into special depressions on the surface of the predatory ball, called digestive pockets, where it is digested.
But especially interesting phenomena in the behavior of myxobacteria are observed when there is a shortage of food resources.
Promotional video:
And if before that the cells of myxobacteria in the total mucous mass were evenly distributed, now they begin to gather in the center of the colony, where more and more new orders of cells arrive. As a result of such active movements of cell masses, the colony thins out at the edges, but in the central part it, as if by leaps and bounds, rises upward.
Moreover, not a shapeless mass, but a completely structured formation: a vertical column grows from a barely noticeable tubercle, in the upper part of which many branches appear. In the end, something like a small tree is formed from the mucous cake, in which the tops of the branches are decorated with strange large "flowers" with many thick "petals".
These tree-like formations reach a height of several millimeters, therefore they are clearly visible without a microscope. In different types of myxobacteria, they can differ in shape, as well as in color, which can be green, yellow or orange. These "flowers" are fruiting bodies and consist essentially of two categories of cells.
Most of them during the growth of the "tree" serves as a building material. They form the "trunk" and "branches" of the fruiting body. But the “flower petals” are a few groups of those cells that, having survived a harsh time, will again return to an active lifestyle.
During the formation of fruiting bodies, bacteria change their rod-like shape to a round one, become covered with dense membranes and turn into dormant cells. When the unfavorable period has passed, they will fall off the branches of the fruiting body, lose their protective shell and again turn into mobile sticks. They will begin to divide again and thus lay the foundation for new generations of myxobacteria …
Fruit bodies of myxobacteria
Naturally, in order, for example, to move in a "formation" or to attack the victim in unison, not to mention more complex behavioral acts, bacteria must somehow. And for communication they have a special - chemical - language, which is most actively used when there are a lot of bacteria.
In this case, each bacterial cell produces certain signaling molecules. And when their number reaches a certain critical point, they become the "voice of the people", to which most of the participants in the "meeting" obey.
Thus, this chemical "conversation" is necessary for bacteria to make collective decisions. In particular, by such molecular communication microorganisms can “count” each other, gather in colonies or synchronize the synthesis and release of toxin into the external environment.
The “universal word” in bacteria is a special signaling substance AI-2, the synthesis of which in different microorganisms is carried out under the control of the same gene. Moreover, despite its versatility, different bacteria respond to this signal in different ways. For example, he can “turn on” the glow of marine microorganisms and open a “communication session” in the E. coli colony.
It should also be said that due to the unequal interpretation of the "language" by different types of bacteria, interspecific conflicts may arise. In addition, some species with the help of this language can control others: for example, having entered into a “dialogue” of competitors, one can conduct it in such a way that one can become the winner in the struggle for one or another resource.
Bacteria are in most cases "predators" that not only attack humans, animals or plants. They are not averse to committing an evil act towards their single-celled relatives.
So, lactobacilli, once in such an environment of other bacteria, are immediately transformed. They begin to vigorously release into the external environment rounded granules with substances harmful to neighbors: lactic acid, lysozyme and some specific proteins.
But the struggle does not go unnoticed for the lactobacilli themselves: their cells are damaged, and the contents of the cytoplasm flow out.
And the more active lactobacilli are, the more damaged cells appear in their rows, which subsequently die. And in the most active strains, more than a third of the participants in mini-battles die. But the bacterial community does not allow the death of all its members - in a critical situation, some of the microbial cells cover their wall with additional protective layers and go into a dormant state.
As for the injured side, it behaves as an army that lost the battle should behave. Some cells of defeated bacteria simply stop reproducing, others gradually collapse, and still others stop contacting each other and an empty space appears between them.