This article, like a biology report for grade 5 on bacteriophage viruses, will help the reader find out basic information about these extracellular life forms. Here we consider their taxonomic location, structural features and vital functions, manifestation of themselves when interacting with bacteria, etc.
Introduction
Everyone knows that the universal representative of the unit of life on planet Earth is the cell. However, the boundary between the nineteenth and twentieth centuries became an era during which a whole series of diseases were discovered that affected animals, plants, and even fungi. By 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 at the same time where even the smallest cell could stop. This led to the discovery of viruses.
Total information
Before considering the representatives of viruses - bacteriophages - let's get acquainted with general information about this kingdom of taxonomic hierarchy.
The viral particle has the smallest sizes (20-300 nm) and symmetrical structuring. Built from constantly repeating components. All organisms of a viral nature are a fragment of RNA or DNA, are enclosed in a special membrane of a protein called a capsid. They do not have the ability to independently function and maintain vital functions, being outside of another cell. The manifestation of the properties of living beings is inherent to them only after being introduced into another organism, while the virus itself will use the resources of the cells it has captured to maintain stability in its own state. It follows that this taxonomy domain is presented as a parasitic, intracellular life form. There are viruses that capture portions of the membranes of the cell in which they developed and lived. They form around such places another shell covering the capsid.
As a rule, viruses form a bond with the surface of the cell in which they parasitize. Next, the virus enters and begins to search for a specific structure that it can infect. For example, the causative agents of hepatitis function and live only in the cellular units of the liver, and mumps tries to penetrate the parotid glands.
The DNA (RNA) belonging to the virus, once inside the host cell, begins to interact with the apparatus of genetic heredity so that the cell itself begins an uncontrolled process of synthesis of a specific series of proteins encoded in the nucleic acid of the pathogen itself. Next, replication takes place, performed directly by the cell itself, and thus begins the process of assembling a new viral particle.
Bacteriophage
What are bacteriophage viruses? This is a special form of life on Earth that selectively penetrates bacteria cells. Reproduction most often occurs inside the carrier, and the process itself leads to lysis. Considering the structure of viruses by the example of bacteriophages, we can conclude that they consist of membranes formed by proteins and have an apparatus for reproducing heredity in the form of one RNA strand or two DNA strands. The total number of bacteriophages approximately corresponds to the total number of bacterial organisms. These viruses are actively involved in the chemical circulation of substances and energy in nature. They cause many manifestations of signs in bacteria and microbes, developed or developing during evolution.
Discovery story
Bacteriology researcher F. Tuort 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 colony of cells to others.
A microbiologist from Canada, F. D'Erell, discovered bacteriophages in September 1917. Their discovery was made regardless of the works of F. Tuorot.
In 1897, N.F. Gamaleya became an observer of the phenomenon of bacterial lysis, which proceeded under the influence of the agent vaccination process.
Bacterial viruses are bacteriophage parasites that play a huge role in the pathogenesis of infections. They are busy ensuring the recovery of the multicellular organism from many diseases, and therefore form a specific type of immune system. For the first time, D'Erell spoke about this, and later developed it into a doctrine. This situation attracted many scientists who began to explore this area and try to find answers to questions such as: what cell structure (crystals) do bacteria-bacteria phage have? What are the processes inside them, their further fate and development? All this and much more has attracted the attention of many researchers.
Value
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 oldest form of viral particles. Quantitative analysis indicates that their population has more than 10 30 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 determined by habitat, by the preferences of the bacteria that they infect, therefore, lysing soil bacteria (phages) will live in the soil. The more microorganisms are contained in the substrate, the more there are necessary phages.
In fact, each bacteriophage embodies one of the basic elemental units of genetic motility. Using transduction, they cause the emergence of new genes in the hereditary material of the bacterium. About 10 24 bacterial cells can be infected per second. This form of answering the question of which viruses are called bacteriophages openly shows us how to distribute hereditary information that occurs between bacterial organisms from the general environment.
Structural features
Answering the question what structure the bacteriophage virus has, it can be concluded that they can be distinguished in accordance with the chemical structure, the type of nucleic acid (NK), 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 phage representative is formed by the head and tail. The length of the tail section can be two to four times the head diameter, in which, incidentally, is the genetic potential, which takes the form of a DNA or RNA chain. There is also an enzyme - transcriptase, immersed in an inactive state and surrounded by a membrane of proteins or lipoproteins. It determines the storage of the genome inside the cell and is called a capsid.
The structural features of the bacteriophage virus determine its tail section as a tube of proteins, which serves as a continuation of the membrane that makes up the head. ATPase is located in the region of the tail base, regenerating the energy resources spent on the process of injection of genetic material.
Systematic data
A bacteriophage is a virus that infects bacteria. That is how it is classified by systematics in a hierarchical table. Assigning them a title in this science was due to the discovery of a huge amount of these organisms. Currently, these issues are being addressed by the ICTV. In accordance with the International Standards for the Classification and Distribution of Taxons among Viruses, bacteriophages are distinguished by the type of nucleic acid they contain or the morphological features.
Today, 20 families can be distinguished, among which only 2 belong to containing RNA and 5 with the presence of 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 in the form of a ring molecule of deoxyribonucleic acid) and other 9 with a linear figure. 9 families are specific for bacteria and the other 9 for archaea.
Effect on the bacterial cell
Bacteriophage viruses, depending on the nature of the interaction with the bacterial cell, can differ into phages of a virulent and moderate type. 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, introduction into the cell structure, processes for the biosynthesis of phage elements and their bringing into a functional state, as well as the exit of the bacteriophage beyond the host.
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 attaches. Using the tail, the phage through the enzymes contained at its completion, destroys the membrane in a specific location of the cell. Then there is its contraction, due to which DNA is introduced into the cell. The “body” of the bacteriophage virus with its protein coat remains outside.
An injection performed by a phage causes a complete rearrangement of all metabolic processes. The synthesis of bacterial proteins, as well as RNA and DNA, is completed, and the bacteriophage itself begins the process of transcription due to the activity of a personal enzyme called transcriptase, which is activated only after the bacteria enter the cell.
Both early and late chains of messenger RNA are synthesized after they enter the ribosome of the host cell. The synthesis of such structures as nuclease, ATPase, lysozyme, capsid, tail process and even DNA polymerase takes place there. The replication process proceeds in accordance with the semi-conservative mechanism and is carried out only in the presence of polymerase. Late proteins are formed after the completion of deoxyribonucleic acid replication processes. After this, the final stage of the cycle begins, in which phage maturation occurs. Also, association with the protein coat and the formation of mature particles ready for infection can occur.
Life cycles
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 a cell with the same cycle:
- phage adsorption process at a specific receptor;
- introducing a nucleic acid injection into a victim;
- the joint process of nucleic acid replication, both phage and bacteria, starts;
- cell division process;
- development lysogenic or lytic.
A moderate bacteriophage maintains a prophage regimen and follows a lysogenic pathway. Virulent representatives develop in accordance with the lytic model, in which there are a number of sequential processes:
- The direction of synthesis of nucleic acids is determined by the enzymes of the phage, which affects 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 cleavage. In the next part of the process, the “subordination” of the cellular apparatus by protein synthesis occurs.
- Phage N. to. undergoes replication and determines the direction of the synthesis of new protein shells. The process of lysozyme formation is subordinate to phage RNA.
- Cell lysis: cell rupture due to lysozyme activity. There is a release of a huge number of new phages that will infect bacterial organisms further.
Operation methods
Bacteriophage viruses are widely used in antibiotic therapy, which serves as an alternative to antibiotics. Among the organisms that may be applicable, they are most often distinguished: streptococcal, staphylococcal, Klebsiella, coli, Proteus, pyobacteriophages, polyprotein and dysentery.
On the territory of the Russian Federation for medical purposes, thirteen pharmaceutical substances based on phages are registered and applicable in practice. 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 the weak sensitivity of the pathogen to the antibiotic itself or to complete resistance. In practice, the use of bacteriophages leads to the rapid and qualitative 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 combat bacteria that cause food poisoning. Many years of experience in studying the activity of bacteriophages show us that the presence, for example, of a dysenteric phage in the total space of cities and villages causes the exposure of the space to preventive measures.
Genetic engineers exploit bacteriophages as vectors by which DNA sites are transferred. And also with their participation, the transfer of genomic information between interacting bacterial cells proceeds.