Is Hiv Lytic Or Lysogenic

Lytic vs Lysogenic – Understanding Bacteriophage Life Cycles

Bacteriophage (phage) are obligate intracellular viruses that specifically infect leaner. They were discovered independently by two researchers, Frederick William Twort¹ at the University of London in 1915, and Félix d'Herelle^two who confirmed the finding and coined the term bacteriophage in 1917 and have been much studied since.

Bacteriophage Structure

Phage have a very simple construction (Figure 1). Their genetic fabric is independent in a prism shaped head, surrounded past a protein capsid. This is continued to the elongated sheath (sometimes called the tail) by a neck or collar region.

The sheath forms a hollow tube through which the viral DNA/RNA is injected into the host cell and is surrounded by protective sheath proteins. At the bottom of the sheath is the base plate to which the tail fibers (usually six) that facilitate attachment to the host cell are fastened.

Figure i. Case construction of a bacteriophage.

In order to reproduce, phage must first enter the host cell. They bind to specific receptors on the bacterial cell surface with their tail fibers (adsorption) and create a pigsty, a process which, along with attachment, is coordinated by the base of operations plate³. A rigid tube is propelled out of the sheath, puncturing a pigsty in the bacterial cell membrane through which they inject their genetic material (Dna or RNA, double or single stranded). They can and then hijack the host prison cell's cellular machinery for their own replication if surrounding conditions are unfavorable in a process called the lytic wheel. Alternatively, they may enter a dormant state, known as the lysogenic cycle, within the host jail cell if conditions are favorable.

Lytic cycle

In the lytic cycle (Figure two), sometimes referred to as virulent infection, the infecting phage ultimately kill the host cell to produce many of their own progeny. Immediately following injection into the host cell, the phage genome synthesizes early proteins that break downwards the host Dna, allowing the phage to take control of the cellular machinery.

What are the steps of the lytic cycle?

There are four steps to the lytic cycle:

Phage zipper
Bacterial jail cell entry
Phage replication
The birth of new phage

To read almost these steps in more particular, see our article:

Understanding the Lytic Cycle – What Are the Steps?

The phage then uses the host cell to synthesize the remaining proteins required to build new phage particles. The heads and sheaths are assembled separately, the new genetic cloth packed into the head and new daughter phage particles constructed. During this process, the host cells gradually become weakened by phage enzymes and eventually burst, releasing on boilerplate 100-200 new phage progeny into the surrounding environment.

Figure 2. Depiction of the stages of the bacteriophage lytic cycle.

Watch the lytic cycle in action hither.

Lysogenic wheel

The lysogenic bike (Figure 3), sometimes referred to as temperate or not-virulent infection, does non kill the host cell, instead using it as a refuge where information technology exists in a dormant state. Following the injection of the phage DNA into the host cell, it integrates itself into the host genome, with the assist of phage-encoded integrases, where it is so termed a prophage. The prophage genome is then replicated passively forth with the host genome as the host prison cell divides for as long as it remains there and does not course the proteins required to produce progeny. As the phage genome is by and large insufficiently small-scale, the bacterial hosts are normally relatively unharmed by this process.

Figure 3. Depiction of the stages of the bacteriophage lysogenic cycle.

Transition from lysogenic to lytic

If a bacterium containing prophage is exposed to stressors, such as UV light, depression food conditions, or chemicals like mitomycin C, prophage may spontaneously extract themselves from the host genome and enter the lytic cycle in a procedure chosen induction.

This procedure, however, is not perfect and prophage may sometimes leave portions of their DNA behind or take portions of host Dna with them when they re-circularize. If they then infect a new host cell, they may transport bacterial genes from i strain to another in a process called transduction. This is i method past which antibiotic resistance genes, toxin and superantigen-encoding genes and other virulence traits may spread through a bacterial population.

Contempo work has shown that transition between lytic and lysogenic infection is also dependent on the abundance of phage in an area as they are able to produce and sense small peptides in a procedure akin to quorum sensing^iv.

Bacterial immunity to phage infection

Not all leaner are helpless against phage assail, possessing an "immune system" that allows them to fight back. CRISPR-Cas, which is now synonymous with genetic modification, was beginning proposed as a bacterial "adaptive allowed arrangement" past Francisco Mojica^five and independently by a group from Université Paris-Sud⁶ in 2005. The CRISPR locus is an assortment of short repeated sequences separated past spacers with unique sequences. These spacer sequences were constitute to have homology to viral and plasmid Deoxyribonucleic acid, including phage. When attacked by a previously unencountered phage, new spacers are added at one side of the CRISPR, making the CRISPR a chronological record of the phage the cell and its ancestors have encountered. In response to phage invasion, the CRISPR sequences are transcribed and, in partnership with Cas proteins, target and destroy the phage sequences that are homologous to the spacers sequences.

Phage as genetic and molecular biology tools

The Lambda phage, originally isolated from Escherichia coli, is one of the best studied phage and formed the basis of many genetic tools. It has even been said that the use of phage as tools ultimately led to the development of molecular biological science as a subject field⁷. In the 1950s, the phage'due south ability to recombine with host Dna was beginning exploited to manipulate the genomes of Salmonella species and and then the process of transduction was born^eight. Since then, it has been used equally a vehicle to move genetic material between many organisms, including fungal gene manipulations⁹ and even human genes. Information technology was thanks to the humble phage that man insulin was offset safely and cheaply produced. It has also opened upwardly applications in high throughput screening of clones, nanomaterial development^ten, antibacterial treatment for food items, equally a diagnostic tool and drug discovery and delivery systems¹¹.

The phage ϕX174 became an unwitting pioneer in 1977 when information technology was the kickoff organism to accept its entire nucleotide sequence adamant thanks to Fred Sanger and colleagues¹².

Phage therapy

Prior to the discovery of antibiotics by Alexander Fleming in 1928, phage were existence explored as a method for treating bacterial infections. In the mail service-antibiotic era, the convenient wide-spectrum activeness of antibiotic treatment meant that in most organization'southward research into phage therapy was abandoned. However, in many of the former Soviet nations where there was a lack of western antibiotics, research into phage therapies continued through necessity. With the increasing global problems of antibiotic resistance, there has been a resurgence in the phage therapy field in recent years. Whilst phage are able to infect and destroy leaner and accept been successfully used to treat life-threatening infection^xiii, their species and even strain specificity and potential for pre-existing immunity of some bacteria mean targeting a phage treatment is currently not a trivial process and must be tailored to the individual infection. This makes information technology costly and lengthy. Consequently, it is currently a last resort and there is still much work required in this field.

The phage family tree

With the increasing availability and affordability of nucleotide sequencing, there has been an explosion in the numbers of phage genomes submitted to databases over the past two decades^xiv .

Phage are classified by the International Committee on Taxonomy of Viruses (ICTV), every bit of their 2017 update, at that place are 19 families of phage that infect bacteria and archaea (Table 1) but as more samples from more remote areas are sequenced this is just likely to grow in the future.

For mobile users, scroll left and right to view the table data below.

Table 1. ICTV taxonomic classification of bacteriophage infecting bacteria and archaea.

References

ane.Twort FW. AN INVESTIGATION ON THE NATURE OF ULTRA-MICROSCOPIC VIRUSES. The Lancet . 1915;186(4814):1241-1243. doi:ten.1016/S0140-6736(01)20383-3

ii.D'Herelle F. On an invisible microbe antagonistic toward dysenteric bacilli: cursory note by Mr. F. D'Herelle, presented by Mr. Roux. 1917. Res Microbiol . 2007;158(7):553-554. doi:x.1016/j.resmic.2007.07.005

three.Taylor NMI, Prokhorov NS, Guerrero-Ferreira RC, et al. Structure of the T4 baseplate and its role in triggering sheath contraction. Nature . 2016;533(7603):346-352. doi:10.1038/nature17971

four.Erez Z, Steinberger-Levy I, Shamir 1000, et al. Communication betwixt viruses guides lysis–lysogeny decisions. Nature . 2017;541(7638):488-493. doi:10.1038/nature21049

v.Mojica FJM, Díez-Villaseñor C, García-Martínez J, Soria Eastward. Intervening sequences of regularly spaced prokaryotic repeats derive from foreign genetic elements. J Mol Evol . 2005;60(2):174-182. doi:10.1007/s00239-004-0046-iii

six.Pourcel C, Salvignol G, Vergnaud G. CRISPR elements in Yersinia pestis acquire new repeats by preferential uptake of bacteriophage Dna, and provide boosted tools for evolutionary studies. Microbiology (Reading) . 2005;151(Pt three):653-663. doi:10.1099/mic.0.27437-0

7.Summers WC. Bacteriophage therapy. Annu Rev Microbiol . 2001;55:437-451. doi:10.1146/annurev.micro.55.ane.437

viii.Zinder ND, Lederberg J. Genetic exchange in Salmonella. J Bacteriol . 1952;64(5):679-699. doi:10.1128/jb.64.5.679-699.1952

ix.Chaveroche MK, Ghigo JM, d'Enfert C. A rapid method for efficient gene replacement in the filamentous fungus Aspergillus nidulans. Nucleic Acids Res . 2000;28(22):E97. doi:x.1093/nar/28.22.e97

10.Chung WJ, Sena M, Merzlyak A, Lee SW. ii.206 - Phages as Tools for Functional Nanomaterials Development. In: Ducheyne P, ed. Comprehensive Biomaterials . Elsevier; 2011:95-111. doi:10.1016/B978-0-08-055294-1.00064-7

11.O'Sullivan L, Buttimer C, McAuliffe O, Bolton D, Coffey A. Bacteriophage-based tools: recent advances and novel applications. F1000Res . 2016;five:2782. doi:10.12688/f1000research.9705.ane

12.Sanger F, Air GM, Barrell BG, et al. Nucleotide sequence of bacteriophage phi X174 Deoxyribonucleic acid. Nature . 1977;265(5596):687-695. doi:10.1038/265687a0

13.Schooley RT, Biswas B, Gill JJ, et al. Development and Use of Personalized Bacteriophage-Based Therapeutic Cocktails To Treat a Patient with a Disseminated Resistant Acinetobacter baumannii Infection. Antimicrob Agents Chemother . 2017;61(10):e00954-17. doi:x.1128/AAC.00954-17

fourteen.Adriaenssens East, Brister JR. How to Proper noun and Classify Your Phage: An Informal Guide. Viruses . 2017;9(4):E70. doi:10.3390/v9040070

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