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Lambda Phage
ENTEROBACTERIA PHAGE λ (LAMBDA PHAGE , COLIPHAGE λ) is a bacterial virus, or bacteriophage , that infects the bacterial species Escherichia coli
Escherichia coli
(E. coli). It was discovered by Esther Lederberg
Esther Lederberg
in 1950 when she noticed that streaks of mixtures of two E. coli strains, one of which treated with ultraviolet light, was "nibbled and plaqued ". The wild type of this virus has a temperate lifecycle that allows it to either reside within the genome of its host through lysogeny or enter into a lytic phase (during which it kills and lyses the cell to produce offspring); mutant strains are unable to lysogenize cells- instead they grow and enter the lytic cycle after superinfecting an already lysogenized cell. The phage particle consists of a head (also known as a capsid ), a tail, and tail fibers (see image of virus below). The head contains the phage's double-strand linear DNA
DNA
genome. During infection, the phage particle recognizes and binds to its host, E. coli, causing DNA in the head of the phage to be ejected through the tail into the cytoplasm of the bacterial cell. Usually, a "lytic cycle " ensues, where the lambda DNA
DNA
is replicated and new phage particles are produced within the cell. This is followed by cell lysis , releasing the cell contents, including virions that have been assembled, into the environment
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Escherichia Coli
_ Bacillus coli communis_ Escherich 1885 _ESCHERICHIA COLI_ (/ˌɛʃᵻˈrɪkiə ˈkoʊlaɪ/ ; also known as _E. COLI_) is a gram-negative , facultatively anaerobic , rod-shaped , coliform bacterium of the genus _ Escherichia
Escherichia
_ that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most _E. coli_ strains are harmless, but some serotypes can cause serious food poisoning in their hosts, and are occasionally responsible for product recalls due to food contamination . The harmless strains are part of the normal flora of the gut , and can benefit their hosts by producing vitamin K2 , and preventing colonization of the intestine with pathogenic bacteria , having a symbiotic relationship. _E. coli_ is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline slowly afterwards. _E. coli_ and other facultative anaerobes constitute about 0.1% of gut flora , and fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease. Cells are able to survive outside the body for a limited amount of time, which makes them potential indicator organisms to test environmental samples for fecal contamination . A growing body of research, though, has examined environmentally persistent _E. coli_ which can survive for extended periods outside of a host
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Virus Classification
VIRUS CLASSIFICATION is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms , virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms. Viruses are mainly classified by phenotypic characteristics, such as morphology , nucleic acid type, mode of replication, host organisms , and the type of disease they cause. Currently, two main schemes are used for the classification of viruses: the International Committee on Taxonomy of Viruses (ICTV) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV. A catalogue of all the world's viruses has been proposed; some related preliminary efforts have been accomplished
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DsDNA Virus
A DNA
DNA
VIRUS is a virus that has DNA
DNA
as its genetic material and replicates using a DNA-dependent DNA
DNA
polymerase . The nucleic acid is usually double-stranded DNA
DNA
(dsDNA) but may also be single-stranded DNA
DNA
(ssDNA). DNA
DNA
viruses belong to either _Group I_ or _Group II_ of the Baltimore classification system for viruses. Single-stranded DNA is usually expanded to double-stranded in infected cells. Although _Group VII_ viruses such as hepatitis B contain a DNA
DNA
genome , they are not considered DNA
DNA
viruses according to the Baltimore classification, but rather reverse transcribing viruses because they replicate through an RNA intermediate. Notable diseases like smallpox , herpes , and chickenpox are caused by such DNA
DNA
viruses
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Caudovirales
Myoviridae Podoviridae Siphoviridae The CAUDOVIRALES are an order of viruses also known as the tailed bacteriophages (cauda is Latin for "tail"). Under the Baltimore classification scheme, the Caudovirales
Caudovirales
are group I viruses as they have double stranded DNA
DNA
(dsDNA) genomes, which can be anywhere from 18,000 base pairs to 500,000 base pairs in length. The virus particles have a distinct shape; each virion has an icosohedral head that contains the viral genome, and is attached to a flexible tail by a connector protein. The order encompasses a wide range of viruses, many of which containing genes of similar nucleotide sequence and function. Some tailed bacteriophage genomes can vary quite significantly in nucleotide sequence, however, even among the same genus. Due to their characteristic structure and possession of potentially homologous genes, it is believed these bacteriophages possess a common origin. There are at least 350 recognised species in this order
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Siphoviridae
SIPHOVIRIDAE is a family of double-stranded DNA
DNA
viruses in the order Caudovirales
Caudovirales
. Bacteria and archaea serve as natural hosts. There are currently 313 species in this family, divided among 47 genera. The characteristic structural features of this family are a nonenveloped head and noncontractile tail. CONTENTS * 1 Structure * 2 Life cycle * 3 Taxonomy * 3.1 Proposed genera * 3.2 Unclassified * 4 References * 5 External links STRUCTURE Viruses
Viruses
in Siphoviridae
Siphoviridae
are non-enveloped , with icosahedral and head-tail geometries (morphotype B1) or a prolate capsid (morphotype B2), and T=7 symmetry. The diameter is around 60 nm. Members of this family are also characterized by their filamentous, cross-banded, noncontractile tails, usually with short terminal and subterminal fibers. Genomes are double stranded and linear, around 50kb in length, containing about 70 genes . The guanine /cytosine content is usually around 52%
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Lambda (genus)
LAMBDA (synonyms Lambda-like viruses, Lambda-like phages, Lambda phage group, Lambda phage) is a genus of viruses in the order Caudovirales , in the family Siphoviridae . Bacteria serve as natural hosts, with transmission achieved through passive diffusion.. There are currently three species in this genus, including the type species Enterobacteria phage lambda . CONTENTS * 1 Taxonomy * 2 Structure * 3 Genome * 4 Life cycle * 5 History * 6 References * 7 External links TAXONOMYGROUP: DSDNA ORDER: CAUDOVIRALES * FAMILY: SIPHOVIRIDAE * GENUS: LAMBDALIKEVIRUS * ENTEROBACTERIA PHAGE HK022 * ENTEROBACTERIA PHAGE HK97 * ENTEROBACTERIA PHAGE LAMBDA STRUCTURELambdalikeviruses are nonenveloped , with a head and tail. The head is about 60 nm in diameter, consisting of 72 capsomers (T=7, levo). GENUS STRUCTURE SYMMETRY CAPSID GENOMIC ARRANGEMENT GENOMIC SEGMENTATION Lambdalikevirus Head-Tail T=7, levo Non-enveloped Linear MonopartiteGENOMEAll three species have been fully sequenced. They range between 39k and 49k nucleotides, with 57 to 73 proteins. All three complete genomes, as well as several similar but unclassified strains, are available here LIFE CYCLEThe virus attaches to the host cell's adhesion receptors using its terminal fiber, and ejects the viral DNA into the host cytoplasm via long flexible tail ejection system
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Lambda
LAMBDA, Λ, λ (uppercase Λ, lowercase λ; Greek : Λάμ(β)δα lam(b)da) is the 11th letter of the Greek alphabet . In the system of Greek numerals lambda has a value of 30. Lambda
Lambda
is related to the Phoenician letter Lamed . Letters in other alphabets that stemmed from lambda include the Latin L and the Cyrillic
Cyrillic
letter El (Л, л). The ancient grammarians and dramatists give evidence to the pronunciation as (λάβδα) in Classical Greek times. In Modern Greek the name of the letter, Λάμδα, is pronounced ; the spoken letter itself has the sound of "l " as with Latinate
Latinate
"L". In early Greek alphabets , the shape and orientation of lambda varied. Most variants consisted of two straight strokes, one longer than the other, connected at their ends. The angle might be in the upper-left, lower-left ("Western" alphabets), or top ("Eastern" alphabets). Other variants had a vertical line with a horizontal or sloped stroke running to the right. With the general adoption of the Ionic alphabet , Greek settled on an angle at the top; the Romans put the angle at the lower-left. The HTML 4 character entity references for the Greek capital and small letter lambda are "" and "", respectively. The Unicode
Unicode
code points for lambda are U+039B and U+03BB
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Phage
A BACTERIOPHAGE /ˈbækˈtɪər.i.oʊˌfeɪdʒ/ , also known informally as a PHAGE /ˈfeɪdʒ/ , is a virus that infects and replicates within a bacterium . The term is derived from "bacteria" and the Greek : φαγεῖν (phagein), "to devour". Bacteriophages are composed of proteins that encapsulate a DNA
DNA
or RNA
RNA
genome , and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes . Phages replicate within the bacterium following the injection of their genome into its cytoplasm . Bacteriophages are among the most common and diverse entities in the biosphere . Bacteriophages are ubiquitous viruses, found wherever bacteria exist. It’s estimated there are more than 1031 bacteriophages on the planet, more than every other organism on Earth, including bacteria, combined. Phages are widely distributed in locations populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 90 years as an alternative to antibiotics in the former Soviet Union
Soviet Union
and Central Europe, as well as in France
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Bacteriophage
A BACTERIOPHAGE /ˈbækˈtɪər.i.oʊˌfeɪdʒ/ , also known informally as a _PHAGE_ /ˈfeɪdʒ/ , is a virus that infects and replicates within a bacterium . The term is derived from "bacteria" and the Greek : φαγεῖν (_phagein_), "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome , and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes . Phages replicate within the bacterium following the injection of their genome into its cytoplasm . Bacteriophages are among the most common and diverse entities in the biosphere . Bacteriophages are ubiquitous viruses, found wherever bacteria exist. It’s estimated there are more than 1031 bacteriophages on the planet, more than every other organism on Earth, including bacteria, combined. Phages are widely distributed in locations populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 90 years as an alternative to antibiotics in the former Soviet Union and Central Europe, as well as in France
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Esther Lederberg
ESTHER MIRIAM ZIMMER LEDERBERG (December 18, 1922 – November 11, 2006) was an American microbiologist and a pioneer of bacterial genetics . Notable contributions include the discovery of the bacterial virus λ , the transfer of genes between bacteria by specialized transduction , the development of replica plating , and the discovery of the bacterial fertility factor F (F plasmid). Lederberg also founded and directed the now defunct Plasmid Reference Center at Stanford University, where she maintained, named, and distributed plasmids of many types, including those coding for antibiotic resistance, heavy metal resistance, virulence , conjugation , colicins , transposons , and other unknown factors. CONTENTS * 1 Early years * 2 Contributions to microbiology and genetics * 2.1 λ bacteriophage and specialized transduction * 2.2 Bacterial Fertility Factor F * 2.3 Replica plating * 2.4 Later contributions * 3 Professional honors * 4 Professional challenges: gender discrimination * 5 Other interests * 5.1 Music * 5.2 Literature * 5.3 Botany
Botany
and botanical gardens * 6 Notable papers * 7 References * 8 External links EARLY YEARSEsther Miriam Zimmer was the first of two children born in the Bronx , New York, to David Zimmer and Pauline Geller Zimmer. Her brother, Benjamin Zimmer, followed in 1923
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Viral Plaque
A VIRAL PLAQUE is a visible structure formed within a cell culture , such as bacterial cultures within some nutrient medium (e.g. agar ). The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as PLAQUES. Counting the number of plaques can be used as a method of virus quantification . These plaques can sometimes be detected visually using colony counters , in much the same way as bacterial colonies are counted; however, they are not always visible to the naked eye, and sometimes can only be seen through a microscope , or using techniques such as staining (e.g. neutral red for eukaryotes or giemsa for bacteria ) or immunofluorescence . Special
Special
computer systems have been designed with the ability to scan samples in batches. Plaques from a virus isolated from a compost heap near UCLA. The bacterium is M. smegmatis . The appearance of the plaque depends on the host strain, virus and the conditions. Highly virulent or lytic strains give clear plaques while strains that only kill a fraction of their hosts (due to partial resistance/lysogeny) or only reduce the rate of cell growth give turbid plaques. Some partially lysogenic phages give bull's-eye plaques with spots or rings of growth in the middle of clear regions of complete lysis
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Temperate (virology)
In VIROLOGY , TEMPERATE refers to the ability of some bacteriophages (notably coliphage λ ) to display a lysogenic life cycle . Many (but not all) temperate phages can integrate their genomes into their host bacterium\'s chromosome, together becoming a lysogen as the phage genome becomes a prophage . A temperate phage is also able to undergo a productive, typically lytic life cycle, where the prophage is expressed, replicates the phage genome, and produces phage progeny, which then leave the bacterium . With phage the term virulent is often used as an antonym to temperate, but more strictly a virulent phage is one that has lost its ability to display lysogeny through mutation rather than a phage lineage with no genetic potential to ever display lysogeny (which more properly would be described as an obligately lytic phage). NOTES * ^ Barksdale, L., and S. B. Ardon. 1974. Persisting bacteriophage infections, lysogeny, and phage conversions. Annu. Rev. Microbiol. 28:265-299. This virus -related article is a stub . You can help by expanding it . * v * t * e Retrieved from "https://en.wikipedia.org/w/index.php?title=Temperateness_(virology) additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy .® is a registered trademark of the Wikimedia Foundation, Inc
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Genome
In modern molecular biology and genetics , a GENOME is the GENETIC MATERIAL of an organism. It consists of DNA (or RNA in RNA viruses ). The genome includes both the genes (the coding regions ), the noncoding DNA and the genetic material of the mitochondria and chloroplasts . CONTENTS * 1 Origin of term * 2 Overview * 3 Sequencing and mapping * 4 Genome compositions * 4.1 Genome size * 4.2 Proportion of non-repetitive DNA * 4.3 Proportion of repetitive DNA * 4.3.1 Tandem repeats * 4.3.2 Interspersed repeats * 4.3.2.1 Retrotransposons * 4.3.2.2 DNA transposons * 5 Genome evolution * 6 See also * 7 References * 8 Further reading * 9 External links ORIGIN OF TERMThe term _genome_ was created in 1920 by Hans Winkler , professor of botany at the University of Hamburg , Germany . The Oxford Dictionary suggests the name is a blend of the words _gene _ and _chromosome _. However, see omics for a more thorough discussion. A few related _-ome_ words already existed—such as _biome _, _rhizome _, forming a vocabulary into which _genome_ fits systematically. OVERVIEWSome organisms have multiple copies of chromosomes : diploid , triploid , tetraploid and so on
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Lysogeny
LYSOGENY, or the LYSOGENIC CYCLE, is one of two cycles of viral reproduction (the lytic cycle being the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage , can be transmitted to daughter cells at each subsequent cell division, and at later events (such as UV radiation or the presence of certain chemicals) can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes , although the method of DNA incorporation is not fully understood. The distinction between lysogenic and lytic cycles is that the spread of the viral DNA occurs through the usual prokaryotic reproduction, while the lytic phage is spread through the production of thousands of individual phages capable of surviving and infecting other cells. The key difference between the lytic cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell. Phages that replicate only via the lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages. In the lysogenic cycle, the phage DNA first integrates into the bacterial chromosome to produce the prophage
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Lytic
The LYTIC CYCLE (/ˈlɪtɪk/ LIT-ək ), is one of the two cycles of viral reproduction (referring to bacterial viruses or bacteriophages), the other being the lysogenic cycle . The lytic cycle results in the destruction of the infected cell and its membrane. A key difference between the lytic and lysogenic phage cycles is that in the lytic phage, the viral DNA
DNA
exists as a separate molecule within the bacterial cell, and replicates separately from the host bacterial DNA. The location of viral DNA
DNA
in the lysogenic phage cycle is within the host DNA, therefore in both cases the virus/phage replicates using the host DNA
DNA
machinery, but in the lytic phage cycle, the phage is a free floating separate molecule to the host DNA. CONTENTS* 1 Description * 1.1 Penetrating * 1.2 Gene regulation biochemistry * 1.3 Maturation and lysis * 2 References DESCRIPTIONBacteriophages that only use the lytic cycle are called virulent phages (in contrast to temperate phages). The lytic cycle is a six-stage cycle. In the first stage, called "penetration", the virus injects its own nucleic acid into a host cell. In some viruses this genetic material is circular and mimics a bacterial plasmid . The virus hijacks the cell's replication and translation mechanisms, using them to make more viruses. Once enough virions have accumulated, specialized viral proteins are allowed to dissolve the bacterial cell wall
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