The virus now can remain in the host for a long time to establish a chronic infection. In a lysogenic cycle, the phage genome also enters the cell through attachment and penetration. However, some viruses can only be transferred by a specific type of insect vector; for example, a particular virus might be transmitted by aphids but not whiteflies. During lysogeny, the prophage will persist in the host chromosome until induction, which results in the excision of the viral genome from the host chromosome. Here is where the main difference between the two cycles occurs. The Lysogenic Cycle. Such an occurrence is called a burst, and the number of virions per bacterium released is described as the burst size. In the case of V. cholera, phage encoded toxin can cause severe diarrhea; in C. botulinum, the toxin can cause paralysis. However, unlike prophage, the provirus does not undergo excision after splicing into the genome. Symptoms of Ebola. The phages infecting these bacteria carry the toxin genes in their genome and enhance the virulence of the host when the toxin genes are expressed. Specialized transduction occurs at the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle. Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections. Uncoating and fusion After the viral membrane fusion with the vesicle membrane, the RNA in the nucleocapsids are released from the vesicle. The immune system becomes overwhelmed and is unable to fight off the infection. This corresponds, in part, to the eclipse period in the growth of the virus population. While some drugs have shown potential in laboratory studies and animal models, they have not been tested in humans for safety and effectiveness. During the maturation phase, new virions are created. This unique recognition can be exploited for targeted treatment of bacterial infection by phage therapy or for phage typing to identify unique bacterial subspecies or strains. On reinfection of a new bacterium, the phage DNA integrates along with the genetic material acquired from the previous host. This process can be as quick. Viral contents are released into the cell, where viral enzymes convert the single-stranded RNA genome into DNA and incorporate it into the host genome. Animal viruses do not always express their genes using the normal flow of genetic informationfrom DNA to RNA to protein. Some viruses reproduce using both methods, while others only use the lytic cycle. 0:13 So that special case is called a retrovirus. If no viable host cells remain, the viral particles begin to degrade during the decline of the culture (see Figure \(\PageIndex{8}\)). Ebola is incurable and deadly. Two days later, Duncan returned to the hospital by ambulance. In what two ways can a virus manage to maintain a persistent infection? However, others may have ssDNA, dsRNA, or ssRNA genomes. Examples of this are demonstrated by the poliovirus, which exhibits tropism for the tissues of the brain and spinal cord, or the influenza virus, which has a primary tropism for the respiratory tract. Hepatitis C virus and HIV are two examples of viruses that cause long-term chronic infections. The pathogen genome replicates and the host cell's metabolic machinery is used to synthesize enzymes and structural components. Generalized transduction occurs when a random piece of bacterial chromosomal DNA is transferred by the phage during the lytic cycle. Being acellular, viruses such as Ebola do not replicate through any type of cell division; rather, they use a combination of host- and virally encoded enzymes, alongside host cell structures, to produce multiple copies of themselves. There are viruses that are capable of remaining hidden or dormant inside the cell in a process called latency. The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. . In the lytic cycle, the phage replicates and causes the host cell to lyse, meaning the host cell dies. 1. lysogenic The virus herpes type I, or HSV-1, causes cold sores. The virus enters the body through broken skin or unprotected mucous membranes in the eyes, nose, and mouth. Consequently, the hijacking of the host cell's mechanism leads to its death or inability to function correctly. They are then transported to the budding sites in the cell membrane. Ebola: Ebola is a rare and deadly virus that causes a high fever, headache, and hemorrhaging. Similar to the lytic cycle, it begins with the attachment and penetration of the virus. Virulent phages typically lead to the death of the cell through cell lysis. Temperate phages, on the other hand, can become part of a host chromosome and are replicated with the cell genome until such time as they are induced to make newly assembled viruses, or progeny viruses. While some drugs have shown potential in laboratory studies and animal models, they have not been tested in humans for safety and effectiveness. (2) Alternatively, the virus may reproduce at a slow rate and be shed by the cell for a very long time. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. However, some viruses can only be transferred by a specific type of insect vector; for example, a particular virus might be transmitted by aphids but not whiteflies. The virus now can remain in the host for a long time to establish a chronic infection. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure \(\PageIndex{4}\)). Then, it is followed by the transcription of the negative-sense RNA into seven mRNA species. Others become proviruses by integrating into the host genome. His condition had deteriorated and additional blood tests confirmed that he has been infected with the Ebola virus. The process in which a bacterium is infected by a temperate phage is called lysogeny. Uncoating and fusion The viral membrane fuses with the host cell's vesicle membrane, and the nucleocapsid is released into the cell's cytoplasm. Filoviruses such as Ebola and Marburg only use the lytic cycle for replication, targeting and destroying epithelial cells, which contributes to the severity of the disease. Is a latent phage undetectable in a bacterium? Release Viral particles bud off using the host cell's plasma membrane. By themselves, viruses do not encode for all of the enzymes necessary for viral replication. In the lytic cycle, the DNA is multiplied many times and proteins are formed using processes stolen from the bacteria. This book uses the Ebola and Marburg only use the lytic cycle for its replication. Like many animal viruses, plant viruses can have either a DNA or RNA genome and be single stranded or double stranded. HSV2 (Herpes simplex virus, type 2 - sexually transmitted) is also lytic, but its counterpart HSV1 (Herpes simplex virus, type 1 - oral herpes) is lysogenic. This flowchart illustrates the mechanism of specialized transduction. The Ebola virus undergoes a lytic cycle, which uses the host cell to produce new viral copies of itself. Dec 20, 2022 OpenStax. Typically, viruses can undergo two types of DNA replication: the lysogenic cycle or the lytic cycle. During the process of excision from the host chromosome, a phage may occasionally remove some bacterial DNA near the site of viral integration. The integrated phage genome is called a prophage. Plant viruses are more similar to animal viruses than they are to bacteriophages. What aspect of the life cycle of a virus leads to the sudden increase in the growth curve? The lytic cycle of a pathogen typically includes the following phases. This corresponds, in part, to the eclipse period in the growth of the virus population. Rochelle has a bachelor's degree in Physics for Teachers from Philippine Normal University-Manila and has completed 30+ units in MS Geology at University of the Philippines-Diliman. There are two types of transduction: generalized and specialized transduction. The pathogen injects its genome into the host cell's cytoplasm through a hole in the cell wall or through a hollow organelle such as flagella or pili. Two days later, Duncan returned to the hospital by ambulance. For additional information about Ebola, please visit the CDC website. Since the phage is integrated into the host genome, the prophage can replicate as part of the host. Ebola is primarily transmitted through direct contact with bodily fluids from infected patients or other species (e.g., gorillas and chimpanzees). The Zaire ebolavirus, more commonly known as the Ebola virus, was linked to severe EVD outbreaks such as the 1976 viral hemorrhagic fever outbreak in Sudan and Congo. The loss of cell adhesion is profoundly damaging to organ tissues. During the lytic cycle of virulent phage, the bacteriophage takes over the cell, reproduces new phages, and destroys the cell. Some viruses have a dsDNA genome like cellular organisms and can follow the normal flow. Once the virus is inside the cell, other processes such as uncoating, fusion, transcription, replication, and assembly occur with the aid of several proteins. It begins with fever, headache, and muscle pain, followed by vomiting, diarrhea, and internal bleeding. Though both pose large threats to human health, one of the viruses that encompass both the lytic cycle as well as the lysogenic cycle is HIV/AIDS. All viruses depend on cells for reproduction and metabolic processes. Which phage life cycle is associated with which forms of transduction? It then hijacks the host cell to replicate, transcribe, and translate the necessary viral components (capsomeres, sheath, base plates, tail fibers, and viral enzymes) for the assembly of new viruses. As an Amazon Associate we earn from qualifying purchases. The virulence genes can be carried within prophages as autonomous genetic elements called morons, which confers an advantage to the bacteria and indirectly benefits the virus through enhanced lysogen survival. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circular replicon in the bacterial cytoplasm. Not only are these drugs untested or unregistered but they are also in short supply. In this minireview we consider the diversity of phage types as based on potential infection strategies, particularly productive or lysogenic along with lytic release versus chronic release, with emphasis on what major variants should be called (see Table 1 for glossary of terms). Generalized transduction occurs when a random piece of bacterial chromosomal DNA is transferred by the phage during the lytic cycle. The asexual transfer of genetic information can allow for DNA recombination to occur, thus providing the new host with new genes (e.g., an antibiotic-resistance gene, or a sugar-metabolizing gene). You can learn more about these viruses at this link. (credit a: modification of work by Erskine Palmer and B.G. Viruses capable of latency may initially cause an acute infection before becoming dormant. It starts by using glycoprotein to bind to the host cell's receptors. Some bacteria, such as Vibrio cholerae and Clostridium botulinum, are less virulent in the absence of the prophage. Viruses cannot replicate on their own. Phage microbiologists discovered decades ago that lysogenic phages . The hospital continued to treat Duncan, but he died several days after being admitted. Examples of this are demonstrated by the poliovirus, which exhibits tropism for the tissues of the brain and spinal cord, or the influenza virus, which has a primary tropism for the respiratory tract. The integrated viral genome is called a provirus. Some viruses carry out this process without destroying the cell. Others become proviruses by integrating into the host genome. With a few exceptions, RNA viruses that infect animal cells replicate in the cytoplasm. Whereas chickenpox affects many areas throughout the body, shingles is a nerve cell-specific disease emerging from the ganglia in which the virus was dormant. Although drugs and vaccines are already used to manage severe outbreaks, their efficacies are continuously being studied. Not only are these drugs untested or unregistered but they are also in short supply. T-even phage is a good example of a well-characterized class of virulent phages. Symptoms may appear anywhere from 2 to 21 days after exposure to the virus. After binding to host receptors, animal viruses enter through endocytosis(engulfment by the host cell) or through membrane fusion (viral envelope with the host cell membrane). Some examples of lysogenic cycles in bacteria include Corynebacterium diphtheriae, Vibrio cholerae, and Clostridium botulinum. Ebola, also known as Ebola virus disease (EVD), is a severe and often deadly illness caused by the Ebola virus. In the lysogenic cycle, phage DNA is incorporated into the host genome, forming a prophage, which is passed on to subsequent generations of cells. Next, the virus is uncoated within the cytoplasm of the cell when the capsid is removed. and you must attribute OpenStax. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Partinscale-bar data from Matt Russell; credit b: Paulo O / Flickr (CC-BY), one-step multiplication curve for bacteriophage. The final stage is release. Ebola undergoes a lytic cycle a mechanism of virus replication that uses the host cell to produce new copies of viral particles and destroy the host cell's DNA. It is not clear why the virus stops replicating within the nerve cells and expresses few viral proteins but, in some cases, typically after many years of dormancy, the virus is reactivated and causes a new disease called shingles (Figure \(\PageIndex{7}\)). Continuous fever, internal bleeding, diarrhea, and vomiting can result in significant loss of electrolytes, blood plasma, and fluid. One of the therapeutic targets considered is the use of small fragments of genetic material called small-interfering RNAs (siRNAs) to inhibit the virus replication process. Public health officials were able to track down 10 high-risk individuals (family members of Duncan) and 50 low-risk individuals to monitor them for signs of infection. Bacteriophages inject DNA into the host cell, whereas animal viruses enter by endocytosis or membrane fusion. There are two licensed vaccines for the Ebola virus, according to WHO. The Ebola virus must enter a living cell and take over its mechanism to produce new viral particles. Lysogeny is widespread in all species of LAB, but it is best studied in the genus Lactococcus. Influenza virus is one of the few RNA viruses that replicates in the nucleus of cells. Retrovirus: Definition, Life Cycle & Example, Psychological Research & Experimental Design, All Teacher Certification Test Prep Courses, The Central Dogma of Biology & Protein Synthesis, What Are Viruses? His condition had deteriorated and additional blood tests confirmed that he has been infected with the Ebola virus. After entering the host cell, the virus synthesizes virus-encoded endonucleases to degrade the bacterial chromosome. Is a latent phage undetectable in a bacterium? Infection in the immune system's dendritic cells also means that the T lymphocytes do not signal the body of the infection, allowing the Ebola virus to replicate rapidly. Figure 21.2 B. Animal viruses do not always express their genes using the normal flow of genetic informationfrom DNA to RNA to protein. There are two types of transduction: generalized and specialized transduction. However, some conditions (e.g., ultraviolet light exposure or chemical exposure) stimulate the prophage to undergo induction, causing the phage to excise from the genome, enter the lytic cycle, and produce new phages to leave host cells. Transduction seems to play an important role in the evolutionary process of bacteria, giving them a mechanism for asexual exchange of genetic information. Medications for infections and management of blood pressure, fever, diarrhea, vomiting, and pain are also administered. View Microbiology Lecture Outline Viruses Revised 2012 for Nester (1).docx from MCB 2010 at Miami Dade College, Miami. Ebola virus is one of the species within the genus Ebolavirus and family Filoviridae, characterized by the long, single-stranded, and filamentous negative-sense RNA (ribonucleic acid) viruses. All other trademarks and copyrights are the property of their respective owners. Figure \(\PageIndex{2}\): A temperate bacteriophage has both lytic and lysogenic cycles. These types of viruses are known as latent viruses and may cause latent infections. The dsDNA can now be replicated, transcribed, and translated similar to host DNA. Entry The host cell engulfs and uptakes large amounts of nutrients, including the virus, through a wave-like or ruffling motion called. In a lysogenic cycle, the phage genome also enters the cell through attachment and penetration. It is lysogenic. During the lysogenic cycle, instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host. This change in the host phenotype is called lysogenic conversion or phage conversion. A prime example of a phage with this type of life cycle is the lambda phage. The integrated viral genome is called a provirus. WHO Ebola Data and Statistics. March 18, 2005. http://apps.who.int/gho/data/view.ebola-sitrep.ebola-summary-20150318?lang=en, https://openstax.org/books/microbiology/pages/1-introduction, https://openstax.org/books/microbiology/pages/6-2-the-viral-life-cycle, Creative Commons Attribution 4.0 International License, Describe the lytic and lysogenic life cycles, Describe the replication process of animal viruses, Describe unique characteristics of retroviruses and latent viruses, Discuss human viruses and their virus-host cell interactions, Describe the replication process of plant viruses. Plant viruses are more similar to animal viruses than they are to bacteriophages. Nine days passed between Duncans exposure to the virus infection and the appearance of his symptoms. The pathogen parts assemble around the genomes. Once a hospital realizes a patient like Duncan is infected with Ebola virus, the patient is immediately quarantined, and public health officials initiate a back trace to identify everyone with whom a patient like Duncan might have interacted during the period in which he was showing symptoms. A prime example of a phage with this type of life cycle is the lambda phage. Attachment is the first stage in the infection process in which the phage interacts with specific bacterial surface receptors (e.g., lipopolysaccharides and OmpC protein on host surfaces). Here, the virus integrates its genetic information with that of the host and then becomes . The growth curve of bacteriophage populations is a, Bacteriophages transfer genetic information between hosts using either. Through macropinocytosis, the host cell engulfs large amounts of nutrients and fluids, taking the virus in with them. Ebola Virus Disease vs. the Bubonic Plague (Black Death), The lytic cycle involves the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell. Given the great suffering and high mortality rates, it is fair to ask whether unregistered and untested medications are better than none at all. The process in which a bacterium is infected by a temperate phage is called lysogeny. An alternative mechanism for viral nucleic acid synthesis is observed in the retroviruses, which are +ssRNA viruses (see Figure \(\PageIndex{6}\)). Transcription and replication The RNA genome is then transcribed into multiple copies of viral mRNA. If a virus has a +ssRNA genome, it can be translated directly to make viral proteins. This occurs through contraction of the tail sheath, which acts like a hypodermic needle to inject the viral genome through the cell wall and membrane. The outbreak in West Africa in 2014 was unprecedented, dwarfing other human . The RdRP is also an important enzyme for the replication of dsRNA viruses, because it uses the negative strand of the double-stranded genome as a template to create +ssRNA. The behavior of the Ebola virus once it enters the body helps experts determine therapeutic targets to aid in treating infected patients: The US Food and Drug Administration (FDA) approved two treatments for the Ebola Virus Disease specifically caused by the species Zaire ebolavirus. Other nearby cells can then be infected with the virus. Lysogenic conversion is a process in which a non-virulent bacteria becomes a highly virulent pathogen by incorporating virulence factors carried on a lysogenic prophage. Further investigations revealed that Duncan had just returned from Liberia, one of the countries in the midst of a severe Ebola epidemic. Eventually, the damage to the immune system results in progression of the disease leading to acquired immunodeficiency syndrome (AIDS). The host cell continues to survive and reproduce, and the virus is reproduced in all of the cell's offspring. The newly synthesized +ssRNA copies can then be translated by cellular ribosomes. The Ebola virus' single-stranded negative-sense RNA is enclosed by nucleoprotein and other viral proteins (e.g., VP35, VP30, etc. A virus in the. The integrated phage genome is called a prophage. This dormant state is known as latency, and these viruses can exist in nerve tissue for long periods without producing new viral particles, only to reactivate periodically and cause skin lesions where replication occurs. On the other hand, is it ethical to withhold potentially life-saving drugs from dying patients? Ebola, however, only goes through the lytic cycle - not the lysogenic cycle. Later that month, the WHO released a report on the ethics of treating patients with the drug. This nucleocapsid serves as the foundation during viral particle assembly and as a template during transcription and replication. Some bacteria, such as Vibrio cholerae and Clostridium botulinum, are less virulent in the absence of the prophage. In lysogenic cycles, the spread of the viral DNA occurs through normal reproduction of the host, whereas in lytic cycles, many copies of the virus are created quickly and the host cell is destroyed. The one-step multiplication curve for a bacteriophage population follows three steps: 1) inoculation, during which the virions attach to host cells; 2) eclipse, during which entry of the viral genome occurs; and 3) burst, when sufficient numbers of new virions are produced and emerge from the host cell. Electron micrograph of a complete Ebola virus particle. Temperate viruses, such as bacteriophages, can undergo both lysogenic and lytic cycles, while virulent viruses only replicate via the lytic cycle. Microbiology Lecture Outline Chapter 13 Viruses I: Acellular Our mission is to improve educational access and learning for everyone. The host cell's DNA is destroyed and the virus takes over the cell's metabolism, creating copies of itself. The lytic cycle is relatively more common, wherein a virus infects a host cell, uses its metabolism to multiply, and then destroys the cell completely. Public health officials were able to track down 10 high-risk individuals (family members of Duncan) and 50 low-risk individuals to monitor them for signs of infection. The lytic cycle is known as the active cycle, whereas the lysogenic cycle is the dormant phase of the virus. It then hijacks the host cell to replicate, transcribe, and translate the necessary viral components (capsomeres, sheath, base plates, tail fibers, and viral enzymes) for the assembly of new viruses. Although the example diagram shown below refers to a bacteriophage and not Ebola, the cycles process is similar. The presence of the phage may alter the phenotype of the bacterium, since it can bring in extra genes (e.g., toxin genes that can increase bacterial virulence). Most plant viruses are transmitted by contact between plants, or by fungi, nematodes, insects, or other arthropods that act as mechanical vectors. It also aids in the viral assembly during the replication stage. By themselves, viruses do not encode for all of the enzymes necessary for viral replication. Many viruses follow several stages to infect host cells. Once a hospital realizes a patient like Duncan is infected with Ebola virus, the patient is immediately quarantined, and public health officials initiate a back trace to identify everyone with whom a patient like Duncan might have interacted during the period in which he was showing symptoms. Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections. The various mechanisms that HIV uses to avoid being cleared by the immune system are also used by other chronically infecting viruses, including the hepatitis C virus. Plant viruses may be enveloped or non-enveloped. Viruses capable of latency may initially cause an acute infection before becoming dormant. Many viruses target specific hosts or tissues. The Lysogenic Cycle However, if a virus contains a ssRNA genome, the host ribosomes cannot translate it until the ssRNA is replicated into +ssRNA by viral RNA-dependent RNA polymerase (RdRP) (see Figure \(\PageIndex{5}\)). As a result, the virus is engulfed. Attachment The virus cannot easily enter the host cell because a cell membrane protects it. The regulation of gene expression in phages is all about how the lytic cycle gets switched to the lysogenic cycle and vice-versa. If the viral genome is RNA, a different mechanism must be used. Symptoms typically start anywhere between two days and three weeks after infection. Is Ebola lytic? All rights reserved. Under the right conditions, the prophage can become active and come back out of the bacterial chromosome, triggering the remaining steps of the lytic cycle (DNA copying and protein synthesis . Of 24,666 suspected or confirmed cases reported, 10,179 people died.9. Corynebacterium diphtheriae, which produces the toxin of diphtheria only when infected by the phage . Vibrio cholerae, which can become toxic and produce cholera toxin when infected with the phage CTX. Ebola is a virus that primarily replicates through the lytic cycle. The Ebola virus causes the rare and deadly Ebola Virus Disease (EVD), which has an average case fatality of 50%. Since the discovery of the virus, the largest outbreak, which started in Guinea and spread across Sierra Leone and Liberia occurred from 2014-2016. This situation is an example of compassionate use outside the well-established system of regulation and governance of therapies. One of the interesting things about the Ebola virus is its ability to replicate through the lytic cycle, a mechanism of virus replication that uses the host cell to produce new copies of viral particles and destroy the host cell's DNA. are licensed under a, Unique Characteristics of Prokaryotic Cells, Unique Characteristics of Eukaryotic Cells, Prokaryote Habitats, Relationships, and Microbiomes, Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria, Isolation, Culture, and Identification of Viruses, Using Biochemistry to Identify Microorganisms, Other Environmental Conditions that Affect Growth, Using Microbiology to Discover the Secrets of Life, Structure and Function of Cellular Genomes, How Asexual Prokaryotes Achieve Genetic Diversity, Modern Applications of Microbial Genetics, Microbes and the Tools of Genetic Engineering, Visualizing and Characterizing DNA, RNA, and Protein, Whole Genome Methods and Pharmaceutical Applications of Genetic Engineering, Using Physical Methods to Control Microorganisms, Using Chemicals to Control Microorganisms, Testing the Effectiveness of Antiseptics and Disinfectants, History of Chemotherapy and Antimicrobial Discovery, Fundamentals of Antimicrobial Chemotherapy, Testing the Effectiveness of Antimicrobials, Current Strategies for Antimicrobial Discovery, Virulence Factors of Bacterial and Viral Pathogens, Virulence Factors of Eukaryotic Pathogens, Major Histocompatibility Complexes and Antigen-Presenting Cells, Laboratory Analysis of the Immune Response, Polyclonal and Monoclonal Antibody Production, Anatomy and Normal Microbiota of the Skin and Eyes, Bacterial Infections of the Skin and Eyes, Protozoan and Helminthic Infections of the Skin and Eyes, Anatomy and Normal Microbiota of the Respiratory Tract, Bacterial Infections of the Respiratory Tract, Viral Infections of the Respiratory Tract, Anatomy and Normal Microbiota of the Urogenital Tract, Bacterial Infections of the Urinary System, Bacterial Infections of the Reproductive System, Viral Infections of the Reproductive System, Fungal Infections of the Reproductive System, Protozoan Infections of the Urogenital System, Anatomy and Normal Microbiota of the Digestive System, Microbial Diseases of the Mouth and Oral Cavity, Bacterial Infections of the Gastrointestinal Tract, Viral Infections of the Gastrointestinal Tract, Protozoan Infections of the Gastrointestinal Tract, Helminthic Infections of the Gastrointestinal Tract, Circulatory and Lymphatic System Infections, Anatomy of the Circulatory and Lymphatic Systems, Bacterial Infections of the Circulatory and Lymphatic Systems, Viral Infections of the Circulatory and Lymphatic Systems, Parasitic Infections of the Circulatory and Lymphatic Systems, Fungal and Parasitic Diseases of the Nervous System, Fundamentals of Physics and Chemistry Important to Microbiology, Taxonomy of Clinically Relevant Microorganisms. 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