Bacteriophages replicate via either the lytic or lysogenic cycle. There are three types of life cycles in caudovirales. 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. When infection of a cell by a bacteriophage results in the production of new virions, the infection is said to be productive. The genetic elements of a bacteriophage is transferred from one bacterium to another through the process of transduction. Lytic cycle life cycle of viruses that result in the lysis of the host bacterium. In lytic cycle the subsequent steps are synthesis of phage components, assembly, maturation and release. Viruses use the host cells to replicate so the antibiotics do not affect the viruses life cycle. Bacteriophage, also called phage or bacterial virus, any of a group of viruses that infect bacteria. The genetic diversity of bacteriophage is extraordinary and phenomenal.
Now customize the name of a clipboard to store your clips. An example of a bacteriophage known to follow the lysogenic cycle and the lytic cycle is the phage lambda of e. During infection a phage attaches to a bacterium and inserts its genetic material into the cell. Two major cycles of multiplication of bacteriophages are. At this point they initiate the reproductive cycle, resulting in lysis of the host cell. Bacteriophage life cycles lytic cycle t even phages phage. P1 has an icosahedral head containing the phage dna attached to a 220nm long tube. Bacteriophages or phages are viruses that infect bacteria.
In the lysogenic cycle, bacteriophages reproduce without killing the host. The lytic pathway is similar to that of virulent phages. Damage to a cell carrying a lambda prophage induces the prophage to exit from the host chromosome and shift to lytic growth green arrows. Antibiotics work on specific processes in the life cycle of the bacteria that either kill the bacteria or stop it from replicating. Antirepression system associated with the life cycle switch in the. In the lysogenic pathway, the virus remains dormant until induction.
The lytic cycle results in the destruction of the infected cell and its membrane. In lysogenic cycle, the lytic vegetative phage becomes integrated with the host cell chromosomes and is converted into prophage without lysis of bacterial cell. P1 is a temperate bacteriophage phage that infects escherichia coli and a some other bacteria. The lytic cycle leads to the death of the host, whereas the lysogenic cycle leads to integration of phage into the host genome. Replication of a virulent phage takes place in the following stages.
Viruses that infect bacteria phages can influence bacterial community dynamics, bacterial genome evolution and ecosystem biogeochemistry. The phage genome can be made of either double or singlestranded dna or rna, depending on the bacteriophage in question. Home microbiology 1 chapter 6 life cycle of t2 phage. Bacteriophages may have a lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both. 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. After infecting bacteria with lytic bacteriophages in the lab, plaques can be seen on the petri plates. After injection, the linear phage dna is circularized. Temperate phages are bacteriophages that can choose between the lytic and the lysogenic pathways of development. Virulent bacteriophages lyse host cells as a result of expression of the phage genome a. Of these phages, the teven phages t2, t4 and t6 are similar in structure, antigenic response and genetics. While lytic phages kill the cells they infect, temperate phages establish a persistent infection of the cell without killing it.
Integrates into cell chromosome, as a prophage site. Genetic recombination occurs between the viral dna and the bacterial genome as the viral dna is inserted into the bacterial chromosome. The cos site results in a circular form of dna which starts the two events. There are many similarities between bacteriophages and animal cell viruses. In this article we will discuss about bacteriophage. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
But sometimes the viral genetic material remains hidden and inactive in the bacterial dna, allowing the host to reproduce. Uv radiation that may damage or kill the host cell, stimulates transcription of the viral dna. The virus that infects bacteria bacteriophages, exhibit 2 different life cycles. Attachment sites on the bacteriophage adsorb to receptor sites on the host bacterium see fig.
To learn more about the book this website supports, please visit its information center. Some phage, like t4, are only capable of lytic growth lysogenic cycle. 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. Bacteriophages capable of a lysogenic life cycle are termed temperate bacteriophages. Intra cellular multiplication of the phage ends in the lysis of the host bacterium and the release of progeny virions.
Pdf structure and morphogenesis of bacteriophage t4. Phages infect bacteria and can propagate in two possible ways. Plaques are small clear areas on the agar surface where the host bacteria have been lysed by lytic. 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. The lytic life cycle is the equivalent of the productive life cycle of animal viruses and consists of the following steps. These cycles are the lysogenic life cycle and the lytic life cycle.
Roles of bacteriophage lambda gene products o and p during early and late phases of infection cycle. A bacteriophage reproduces by one of two types of life cycles. The process of a phage infecting a bacterium and producing progeny is referred to as a lytic infection. The revitalization of phage therapy has received increased global attention since the appearance of multidrugresistant bacteria. Depending on the life cycle, phages can either by lytic virulent or lysogenic temperate. 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.
As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is replicated in all offspring of the cell. 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. Thus, bacteriophage can be viewed as model systems for animal cell viruses. The lytic phage life cycle involves freephage diffusion, host cell adsorption, an eclipse period, a period of progeny. Bacteriophages were discovered independently by frederick w. Bacteriophages inject dna into the host cell, whereas animal viruses enter by endocytosis or membrane fusion.
In the lytic cycle, a bacteriophage infects a bacteria and kills it to release progeny virus. The term phage is an abbreviation of the word bacteriophage. Some bacteriophages have the ability to perform both lytic and lysogenic cycles. 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. The phages undergoing lytic cycle are called lytic phages or virulent phages, e. Bacteriophages that replicate through the lytic life cycle are called lytic bacteriophages.
In the lysogenic cycle, the viral dna circularizes and integrates into the host dna. Assembly formation new virus parts are assembled in the cytoplasm 11. The role of phage lysozyme in the life cycle of phage t4. They can have either lytic or lysogenic cycle, depending on the environment. Download fulltext pdf download fulltext pdf download fulltext pdf alternative bacteriophage life cycles.
The process of transduction can be specialized or generalized. In lytic cycle, a lytic phage infects and kills the host cell to release progeny. Bacteriophages that only use the lytic cycle are called virulent phages in contrast to temperate phages. 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. Some phage, like t4, are only capable of lytic growth. In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host 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. Lytic or virulent phages are phages, which multiply in bacteria and kill the cell by lysis at the end of the life cycle. Soon after the nucleic acid is injected, the phage cycle is said to be in eclipse period. Bacteriophage latentperiod evolution as a response to resource. Other phages can alternate between a lytic lifecycle and a lysogenic lifecycle.
The host specificity of bacteriophages is very high, thus enabling classification of bacteria on this specificity. When the lambda dna enters the cell the ends join to form a circular dna molecule. How do lytic and lysogenic cycle of bacteriophage differ. The circle mode of replication of bacteriophage lambda. As a result, spc32n could not establish lysogeny as clear plaque mutants. Clipping is a handy way to collect important slides you want to go back to later. When undergoing a lysogenic cycle the phage genome exists as a autonomous plasmid, that is maintained at low copy number, in the bacterium.
T even phages phage quickly replicates killing host cell lytic burst. 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. Viral dna destroys cell dna, takes over cell functions and destroys the cell. 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. In general the life cycle of most phages at 37c varies between 22 and 60 minutes. Roles of bacteriophage lambda gene products o and p during. Bacteriophages exhibit two types of replication cycle virulent or lytic cycle and temperate or lysogenic cycle fig. This is called lytic replication, a cycle which ends when the new phages burst out, killing the host bacterium. Photo courtesy of michel wurtz and the biocenter at the university of basel. Bacteriophage structure and life cycle of bacteriophage. During the eclipse phase, no infectious phage particles can.
Most bacteriophages adsorb to the bacterial cell wall, although some are able to adsorb to flagella or pili. For temperate bacteriophages, the introduction of certain events e. The phage infects a bacterium and inserts its dna into the. Medical visualisation of the bacteriophage lytic cycle. Applications of bacteriophages versus phage enzymes to combat. Get a printable copy pdf file of the complete article 1. Bacteriophage exhibits two major types of life cycles. Differences between lytic and lysogenic cycles in the lytic cycle. 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.