This article, like a 5th grade biology report on bacteriophage viruses, will help the reader learn basic information about these extracellular life forms. Here we will consider their taxonomic location, features of structure and life activity, manifestation of themselves when interacting with bacteria, etc.
Introduction
Everyone knows that the universal representative of a unit of life on planet Earth is a cell. However, the turn between the nineteenth and twentieth centuries was an era during which a number of diseases were discovered that affect animals, plants, and even fungi. Analyzing this phenomenon and taking into account general information about human diseases, scientists realized that there are organisms that can be of a non-cellular nature.
Such creatures are extremely small, and therefore able to pass through the smallest filter without stopping where even the smallest cell could stop. This led to the discovery of viruses.
General data
Beforeconsider representatives of viruses - bacteriophages - let's get acquainted with general information about this kingdom of the taxonomic hierarchy.
The virus particle has the smallest dimensions (20-300 nm) and symmetrical structuring. It is built from constantly repeating components. All organisms of a viral nature are a fragment of RNA or DNA, enclosed in a special protein shell called a capsid. They do not have the ability to independently function and maintain vital activity, being outside another cell. The manifestation of the properties of living beings is inherent in them only after being introduced into another organism, while the virus itself will use the resources of the cell it has captured to maintain stability in its own state. It follows that this domain of taxonomy is presented as a parasitic, intracellular life form. There are viruses that capture sections of the membranes of the cell in which they developed and lived. They form another shell around such places, covering the capsid.
As a rule, viruses form a bond with the surface of the cell in which they parasitize. Then the virus gets inside and starts looking for a specific structure that it can hit. For example, the causative agents of hepatitis function and live only in the cell units of the liver, while mumps tries to penetrate into the parotid glands.
DNA (RNA) belonging to the virus, once inside the carrier cell, begins to interact with the apparatus of genetic heredity so that the cell itself begins an uncontrolled synthesis processa specific series of proteins encoded in the nucleic acid of the pathogen itself. Next, replication takes place, which is carried out directly by the cell itself, and thus the process of assembling a new viral particle begins.
Bacteriophage
Who are bacteriophage viruses? This is a special form of life on Earth that selectively penetrates bacteria cells. Reproduction most often occurs within the host, and the process itself leads to lysis. Considering the structure of viruses using the example of bacteriophages, we can conclude that they consist of shells formed by proteins and have an apparatus for reproducing heredity in the form of one RNA chain or two DNA chains. The total number of bacteriophages approximately corresponds to the total number of bacterial organisms. These viruses take an active part in the chemical circulation of substances and energy in nature. Cause many manifestations of signs in bacteria and microbes developed or developing in the course of evolution.
Discovery history
Bacteriology researcher F. Twort created a description of an infectious disease, which he proposed in an article published in 1915. This disease affected staphylococci and could pass through any filters, and could also be transported from one cell colony to others.
F. D'Herelle, a Canadian-born microbiologist, discovered bacteriophages in September 1917. Their discovery was made independently of the work of F. Tworot.
In 1897, N. F. Gamaleya became an observer of the phenomenon of lysisbacteria that proceeded under the influence of the grafting agent process.
Bacterial viruses are parasitic bacteriophages that play a huge role in the pathogenesis of infections. They are engaged in ensuring the recovery of the multicellular type of organism from many diseases, and therefore form a specific type of immune system. D'Herelle first spoke of this, and later developed it into a doctrine. This position attracted many scientists who began to explore this area and try to find answers to questions such as: what kind of cellular structure (crystals) do bacteria-viruses bacteriophages have? What are the processes inside them, their further fate and development? All this and more has attracted the attention of many researchers.
Meaning
The structure of viruses on the example of a bacteriophage can tell us a lot, especially for interaction with other information that a person has about them. For example, they are supposedly the most ancient form of virus particles. Quantitative analysis indicates to us that their population has more than 1030 particles.
In nature, they can be found in the same place where bacteria live, to which they can be sensitive. Since the organisms in question are defined by their habitat, by the preferences of the bacteria they infect, it follows that lysing soil bacteria (phages) will live in the soil. The more microorganisms there are in the substrate, the more necessary phages there.
In reality, every bacteriophage embodiesone of the basic elemental units of genetic mobility. Using transduction, they cause the emergence of new genes in the hereditary material of the bacterium. About 1024 bacterial cells can be infected per second. This form of answering the question of which viruses are called bacteriophages openly shows us the ways in which hereditary information is distributed between bacterial organisms from a common habitat.
Building features
Answering the question of what structure a bacteriophage virus has, we can conclude that they can be distinguished in accordance with the chemical structure, the type of nucleic acid (n.c.), morphological data and the form of interaction with bacterial organisms. The size of such an organism can be several thousand times smaller than the microbial cell itself. A typical representative of phages is formed by a head and a tail. The length of the tail can be two to four times the diameter of the head, which, by the way, houses the genetic potential, which has taken the form of a DNA or RNA chain. There is also an enzyme - transcriptase, immersed in an inactive state and surrounded by a shell of proteins or lipoproteins. It determines the storage of the genome inside the cell and is called the capsid.
The structural features of the bacteriophage virus define its tail compartment as a tube of proteins, which serves as a continuation of the shell that makes up the head. ATPase is located in the region of the tail base, which regenerates the energy resources spent on the injection process.genetic material.
Systematic data
Bacteriophage is a virus that infects bacteria. This is how the taxonomist classifies it in the table of hierarchical order. The assignment of a title to them in this science was due to the discovery of a huge amount of these organisms. These issues are currently being addressed by the ICTV. In accordance with the International Standards for the classification and distribution of taxa among viruses, bacteriophages are distinguished by the type of nucleic acid they contain or morphological features.
Today, 20 families can be distinguished, among which only 2 belong to containing RNA and 5 with a shell. Among DNA viruses, only 2 families have a single-stranded form of the genome. 9 viruses containing DNA (the genome appears to us as a circular molecule of deoxyribonucleic acid) and the other 9 with a linear figure. 9 families are specific to bacteria, and the other 9 are specific to archaea.
Influence on the bacterial cell
Bacteriophage viruses, depending on the nature of interaction with a bacterial cell, can differ in virulent and moderate type phages. The former are able to increase their number only with the help of lytic cycles. The processes in which the interaction of the virulent phage and the cell occurs, consists of adsorption on the cell surface, penetration into the cell structure, processes for the biosynthesis of phage elements and their bringing into a functional state, as well as the release of the bacteriophage from the host.
Let's consider the description of bacteriophage viruses based on their further action in the cell.
Bacteria have on their surface special phage-specific structures, presented in the form of receptors, to which, in fact, the bacteriophage is attached. Using the tail, the phage, by means of the enzymes contained at its end, destroys the membrane in a certain location of the cell. Further, its contraction occurs, as a result of which DNA is introduced into the cell. The "body" of the bacteriophage virus with its protein coat remains outside.
Injection made by a phage causes a complete restructuring of all metabolic processes. The synthesis of bacterial proteins, as well as RNA and DNA, is completed, and the bacteriophage itself begins the transcription process thanks to the activity of a personal enzyme called transcriptase, which is activated only after entering the bacterial cell.
Both early and late strands of messenger RNA are synthesized after they enter the ribosome of the carrier cell. The process of synthesis of such structures as nuclease, ATPase, lysozyme, capsid, tail process and even DNA polymerase also takes place there. The replication process proceeds in accordance with a semi-conservative mechanism and is carried out only in the presence of a polymerase. Late proteins are formed after the completion of the processes of replication of deoxyribonucleic acid. After this, the final stage of the cycle begins, in which phage maturation occurs. It can also combine with the protein shell and form mature particles ready for infection.
Cycles of life
Regardless of the structure of the bacteriophage virus, they all have a common characteristic of life cycles. In accordance with moderation or virulence, both types of organisms are similar to each other in the initial stages of influence on the cell with the same cycle:
- the process of phage adsorption on a specific receptor;
- injecting nucleic acids into the victim;
- starts the joint process of replication of nucleic acids, both phage and bacteria;
- cell division process;
- development by lysogenic or lytic way.
The temperate bacteriophage maintains the prophage mode, follows the lysogenic pathway. Virulent representatives develop in accordance with the lytic model, in which there are a number of sequential processes:
- The direction of nucleic acid synthesis is set by phage enzymes, which affect the apparatus responsible for protein synthesis. The parasite begins the inactivation of RNA and DNA belonging to the host, and further enzymatic action completely leads to its splitting. The next part of the process is the "subordination" of the cellular apparatus for protein synthesis.
- Phage n. to. undergoes replication and determines the direction of the synthesis of new protein shells. The process of formation of lysozyme is subordinate to phage RNA.
- Cell lysis: Cell rupture caused by lysozyme activity. A huge number of new phages are released, which will infect bacterial organisms further.
Methods of operation
Virusesbacteriophages find their wide application in antibacterial type therapy, which serves as an alternative to antibiotics. Among the organisms that may be applicable, the most commonly distinguished are: streptococcal, staphylococcal, klebsiella, coli, proteus, pyobacteriophages, polyproteins and dysentery.
Thirteen medicinal substances based on phages are registered and applied in practice on the territory of the Russian Federation for medical purposes. As a rule, such methods of fighting infections are used when the traditional form of treatment does not lead to significant changes, which is caused by a weak sensitivity of the pathogen to the antibiotic itself or complete resistance. In practice, the use of bacteriophages leads to a quick and high-quality achievement of the desired success, but this requires the presence of a biological membrane covered with a layer of polysaccharides, through which antibiotics cannot penetrate.
The therapeutic type of application of phage representatives does not find support in the West. However, it is often used to fight bacteria that cause food poisoning. Many years of experience in studying the activity of bacteriophages show us that the presence, for example, of the dysentery phage in the common space of cities and villages causes the exposure of the space to preventive measures.
Genetic engineers exploit bacteriophages as vectors to transfer DNA segments. And also with their participation, the transfer of genomic information takes placebetween interacting bacterial cells.
