Soon after the nucleic acid is injected, the phage cycle is said to be in eclipse period. Lytic or virulent phages are phages, which multiply in bacteria and kill the cell by lysis at the end of the life cycle. Now customize the name of a clipboard to store your clips. Bacteriophages or phages are viruses that infect bacteria. P1 is a temperate bacteriophage phage that infects escherichia coli and a some other bacteria. Antibiotics work on specific processes in the life cycle of the bacteria that either kill the bacteria or stop it from replicating. Replication of a virulent phage takes place in the following stages. The genetic diversity of bacteriophage is extraordinary and phenomenal.
Roles of bacteriophage lambda gene products o and p during. As a result, spc32n could not establish lysogeny as clear plaque mutants. In the lysogenic cycle, bacteriophages reproduce without killing the host. In lytic cycle, a lytic phage infects and kills the host cell to release progeny. The process of transduction can be specialized or generalized. Attachment sites on the bacteriophage adsorb to receptor sites on the host bacterium see fig. At this point they initiate the reproductive cycle, resulting in lysis of the host cell. Phages infect bacteria and can propagate in two possible ways. Bacteriophages may have a lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both.
Some phage are also capable of maintaining their chromosome in a stable, silent state within the bacteria. Some phage, like t4, are only capable of lytic growth. The lytic cycle results in the destruction of the infected cell and its membrane. Generally, the virus continues lytic cycle with a few numbers of infected cells, but major portion enters into lysogenic relationship and continues the lysogenic cycle. In the lysogenic pathway, the virus remains dormant until induction. There are many similarities between bacteriophages and animal cell viruses. The genetic elements of a bacteriophage is transferred from one bacterium to another through the process of transduction. Uv radiation that may damage or kill the host cell, stimulates transcription of the viral dna.
Viral dna destroys cell dna, takes over cell functions and destroys the cell. The prophage may be converted into a virulent vegetative lytic phase spontaneously or by physical and chemical agents uv rays, h 20 2, nitrogen mustard. But sometimes the viral genetic material remains hidden and inactive in the bacterial dna, allowing the host to reproduce. In this article we will discuss about bacteriophage. Home microbiology 1 chapter 6 life cycle of t2 phage. Lysogenic cycle attachment penetration prophage cell division biosynthesis maturation release life cycle of animal viruses attachment penetration uncoating biosyntehsis release dna animal virus bacteriophage life cycle lytic cycle attachment penetration biosynthesis maturation release bacteriophage life cycle. Antirepression system associated with the life cycle switch in the.
Clipping is a handy way to collect important slides you want to go back to later. Download fulltext pdf download fulltext pdf download fulltext pdf alternative bacteriophage life cycles. Integrates into cell chromosome, as a prophage site. Viruses use the host cells to replicate so the antibiotics do not affect the viruses life cycle. The virus that infects bacteria bacteriophages, exhibit 2 different life cycles. The circle mode of replication of bacteriophage lambda. When the lambda dna enters the cell the ends join to form a circular dna molecule. In lysogenic cycle, the lytic vegetative phage becomes integrated with the host cell chromosomes and is converted into prophage without lysis of bacterial cell. Bacteriophages capable of a lysogenic life cycle are termed temperate bacteriophages. The term phage is an abbreviation of the word bacteriophage. Bacteriophages were discovered independently by frederick w. The lytic pathway is similar to that of virulent phages. T even phages phage quickly replicates killing host cell lytic burst.
The phage infects a bacterium and inserts its dna into the. In general the life cycle of most phages at 37c varies between 22 and 60 minutes. The action of most of viral genes is to enable the viruses to infect their respective host cells, multiply by using the host machinery such as enzymes and ribosomes and then causing the lysis of cells. Temperate phages are bacteriophages that can choose between the lytic and the lysogenic pathways of development. After infecting bacteria with lytic bacteriophages in the lab, plaques can be seen on the petri plates.
How do lytic and lysogenic cycle of bacteriophage differ. This is called lytic replication, a cycle which ends when the new phages burst out, killing the host bacterium. Bacteriophages replicate via either the lytic or lysogenic cycle. Assembly formation new virus parts are assembled in the cytoplasm 11. The host specificity of bacteriophages is very high, thus enabling classification of bacteria on this specificity. Bacteriophage t4 is one of the seven escherichia coli phages t1t7, t for type, which, in 1944, were suggested by delbruck and coworkers to be models for study by the phage community. A bacteriophage reproduces by one of two types of life cycles. There are three types of life cycles in caudovirales.
Photo courtesy of michel wurtz and the biocenter at the university of basel. When undergoing a lysogenic cycle the phage genome exists as a autonomous plasmid, that is maintained at low copy number, in the bacterium. Pdf structure and morphogenesis of bacteriophage t4. Bacteriophage latentperiod evolution as a response to resource.
In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. The phages undergoing lytic cycle are called lytic phages or virulent phages, e. Roles of bacteriophage lambda gene products o and p during early and late phases of infection cycle. In addition a knowledge of the life cycle of bacteriophage is necessary to understand one of the mechanisms by which bacterial genes can be transferred from one bacterium to another. Learn vocabulary, terms, and more with flashcards, games, and other study tools. During the eclipse phase, no infectious phage particles can. Of these phages, the teven phages t2, t4 and t6 are similar in structure, antigenic response and genetics. Other phages can alternate between a lytic lifecycle and a lysogenic lifecycle. The lytic cycle leads to the death of the host, whereas the lysogenic cycle leads to integration of phage into the host genome. Some phage, like t4, are only capable of lytic growth lysogenic cycle. Depending on the life cycle, phages can either by lytic virulent or lysogenic temperate.
Most bacteriophages adsorb to the bacterial cell wall, although some are able to adsorb to flagella or pili. Differences between lytic and lysogenic cycles in the lytic cycle. Damage to a cell carrying a lambda prophage induces the prophage to exit from the host chromosome and shift to lytic growth green arrows. When a temperate bacteriophage infects a bacterium, it can either replicate by means of the lytic life cycle and cause lysis of the host bacterium, or, it can incorporate its dna into the bacteriums dna and become a noninfectious prophage see figure 1. Plaques are small clear areas on the agar surface where the host bacteria have been lysed by lytic. In the lysogenic cycle, the viral dna circularizes and integrates into the host dna. Genetic recombination occurs between the viral dna and the bacterial genome as the viral dna is inserted into the bacterial chromosome. The life cycle of bacteriophages has been a good model for understanding how viruses affect the cells they infect, since similar processes have been observed for eukaryotic viruses, which can cause immediate death of the cell or establish a latent or chronic infection. While both life cycles have potential applications in bacteriophage therapy, the lytic cycle seems most suited to antibacterial therapy. The phage genome can be made of either double or singlestranded dna or rna, depending on the bacteriophage in question. After injection, the linear phage dna is circularized. The lytic phage life cycle involves freephage diffusion, host cell adsorption, an eclipse period, a period of progeny.
Get a printable copy pdf file of the complete article 1. Bacteriophages exhibit two types of replication cycle virulent or lytic cycle and temperate or lysogenic cycle fig. The cos site results in a circular form of dna which starts the two events. In lytic cycle the subsequent steps are synthesis of phage components, assembly, maturation and release. These cycles are the lysogenic life cycle and the lytic life cycle. To learn more about the book this website supports, please visit its information center. An example of a bacteriophage known to follow the lysogenic cycle and the lytic cycle is the phage lambda of e.
Bacteriophages that only use the lytic cycle are called virulent phages in contrast to temperate phages. For temperate bacteriophages, the introduction of certain events e. Bacteriophage life cycles lytic cycle t even phages phage. Medical visualisation of the bacteriophage lytic cycle. Some bacteriophages have the ability to perform both lytic and lysogenic cycles.
Virulent bacteriophages lyse host cells as a result of expression of the phage genome a. Applications of bacteriophages versus phage enzymes to combat. Lytic cycle life cycle of viruses that result in the lysis of the host bacterium. They can have either lytic or lysogenic cycle, depending on the environment. Thus, bacteriophage can be viewed as model systems for animal cell viruses. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is replicated in all offspring of the cell. Intra cellular multiplication of the phage ends in the lysis of the host bacterium and the release of progeny virions. Virology 36, 387391 1968 the role of phage lysozyme in the life cycle of phage t4 joyce emrich and george streisinger institute of molecular biology, university of oregon, eugene, oregon 97403 accepted july 29, 1968 the lysozyme that is synthesized under the direction of the e gene of phage t4 is known to cause the lysis of infected bacteria. In the lytic cycle, a bacteriophage infects a bacteria and kills it to release progeny virus. While lytic phages kill the cells they infect, temperate phages establish a persistent infection of the cell without killing it. Bacteriophage structure and life cycle of bacteriophage. Two major cycles of multiplication of bacteriophages are.
Every year around the time the leaves start to turn brilliant colors of gold and red, youre reminded to grab a scarf, drink some hot apple cider and get your flu shot. Bacteriophage exhibits two major types of life cycles. Bacteriophage, also called phage or bacterial virus, any of a group of viruses that infect bacteria. The revitalization of phage therapy has received increased global attention since the appearance of multidrugresistant bacteria. The lytic cycle of a virulent bacteriophage shows the stages of a adsorption, b penetration, c synthesis of the phage components, and d release of progeny phages. In this cycle,phage dna becomes integrated with the bacterial genome and replicates with the bacteria synchronously without causing any harm to the host cell. When infection of a cell by a bacteriophage results in the production of new virions, the infection is said to be productive.
439 895 39 364 183 62 1436 387 636 167 56 329 974 665 1218 201 1165 405 1414 530 24 1526 1472 759 565 1043 1163 159 1220 1486 554 1470 1104 1091 778 785 739 1486 429 941 175 27 1491 1439 462 378 1077 426 230