A least-squares program was used to derive the values of the parameters for a variety of experimental results obtained with wild-type T4 in E. Hadas, M. Einav, I. Fishov, and A. Zaritsky, Microbiology —,
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Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome , and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes e. MS2 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.
It is estimated there are more than 10 31 bacteriophages on the planet, more than every other organism on Earth, including bacteria, combined. Phages have been used since the late 19th century as an alternative to antibiotics in the former Soviet Union and Central Europe, as well as in France. Bacteriophages occur abundantly in the biosphere, with different genomes, and lifestyles.
It has been suggested that members of Picobirnaviridae infect bacteria, but not mammals. Another proposed family is " Autolykiviridae " dsDNA. In , Ernest Hanbury Hankin reported that something in the waters of the Ganges and Yamuna rivers in India had a marked antibacterial action against cholera and it could pass through a very fine porcelain filter.
He believed the agent must be one of the following:. Twort's research was interrupted by the onset of World War I , as well as a shortage of funding and the discoveries of antibiotics. He also recorded a dramatic account of a man suffering from dysentery who was restored to good health by the bacteriophages. They had widespread use, including treatment of soldiers in the Red Army.
However, they were abandoned for general use in the West for several reasons:. The first regulated, randomized, double-blind clinical trial was reported in the Journal of Wound Care in June , which evaluated the safety and efficacy of a bacteriophage cocktail to treat infected venous ulcers of the leg in human patients. The study's results demonstrated the safety of therapeutic application of bacteriophages, but did not show efficacy.
The authors explained that the use of certain chemicals that are part of standard wound care e. Additionally, there have been numerous animal and other experimental clinical trials evaluating the efficacy of bacteriophages for various diseases, such as infected burns and wounds, and cystic fibrosis associated lung infections, among others. Meanwhile, bacteriophage researchers have been developing engineered viruses to overcome antibiotic resistance , and engineering the phage genes responsible for coding enzymes that degrade the biofilm matrix, phage structural proteins, and the enzymes responsible for lysis of the bacterial cell wall.
Therapeutic efficacy of a phage cocktail was evaluated in a mice model with nasal infection of multidrug-resistant MDR A. Mice treated with the phage cocktail showed a 2. Without effective antibiotics the patient was subjected to phage therapy using a phage cocktail containing nine different phages that had been demonstrated to be effective against MDR A.
Once on this therapy the patient's downward clinical trajectory reversed, and returned to health. D'Herelle "quickly learned that bacteriophages are found wherever bacteria thrive: in sewers, in rivers that catch waste runoff from pipes, and in the stools of convalescent patients. Dairy industry — Bacteriophages present in the environment can cause fermentation failures of cheese starter cultures.
In order to avoid this, mixed-strain starter cultures and culture rotation regimes can be used. Diagnostics — In , the FDA cleared the first bacteriophage-based product for in vitro diagnostic use.
The test returns results in about five hours, compared to two to three days for standard microbial identification and susceptibility test methods. It was the first accelerated antibiotic-susceptibility test approved by the FDA. Counteracting bioweapons and toxins — Government agencies in the West have for several years been looking to Georgia and the former Soviet Union for help with exploiting phages for counteracting bioweapons and toxins, such as anthrax and botulism. Other uses include spray application in horticulture for protecting plants and vegetable produce from decay and the spread of bacterial disease.
Other applications for bacteriophages are as biocides for environmental surfaces, e. The technology for phages to be applied to dry surfaces, e. Clinical trials reported in Clinical Otolaryngology  show success in veterinary treatment of pet dogs with otitis.
The SEPTIC bacterium sensing and identification method uses the ion emission and its dynamics during phage infection and offers high specificity and speed for detection. Phage display is a different use of phages involving a library of phages with a variable peptide linked to a surface protein. Each phage genome encodes the variant of the protein displayed on its surface hence the name , providing a link between the peptide variant and its encoding gene.
Variant phages from the library may be selected through their binding affinity to an immobilized molecule e. The bound, selected phages can be multiplied by reinfecting a susceptible bacterial strain, thus allowing them to retrieve the peptides encoded in them for further study. Antimicrobial drug discovery — Phage proteins often have antimicrobial activity and may serve as leads for peptidomimetics , i.
Basic research — Bacteriophages are important model organisms for studying principles of evolution and ecology. Bacteriophages may have a lytic cycle or a lysogenic cycle.
With lytic phages such as the T4 phage , bacterial cells are broken open lysed and destroyed after immediate replication of the virion. As soon as the cell is destroyed, the phage progeny can find new hosts to infect. Lytic phages are more suitable for phage therapy. Some lytic phages undergo a phenomenon known as lysis inhibition, where completed phage progeny will not immediately lyse out of the cell if extracellular phage concentrations are high.
This mechanism is not identical to that of temperate phage going dormant and usually, is temporary. In contrast, the lysogenic cycle does not result in immediate lysing of the host cell. Those phages able to undergo lysogeny are known as temperate phages. Their viral genome will integrate with host DNA and replicate along with it, relatively harmlessly, or may even become established as a plasmid. The virus remains dormant until host conditions deteriorate, perhaps due to depletion of nutrients, then, the endogenous phages known as prophages become active.
At this point they initiate the reproductive cycle, resulting in lysis of the host cell. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is replicated in all offspring of the cell. An example of a bacteriophage known to follow the lysogenic cycle and the lytic cycle is the phage lambda of E. Sometimes prophages may provide benefits to the host bacterium while they are dormant by adding new functions to the bacterial genome , in a phenomenon called lysogenic conversion.
Examples are the conversion of harmless strains of Corynebacterium diphtheriae or Vibrio cholerae by bacteriophages, to highly virulent ones that cause diphtheria or cholera , respectively.
Bacterial cells are protected by a cell wall of polysaccharides , which are important virulence factors protecting bacterial cells against both immune host defenses and antibiotics. This specificity means a bacteriophage can infect only certain bacteria bearing receptors to which they can bind, which in turn, determines the phage's host range.
Polysaccharide-degrading enzymes, like endolysins are virion-associated proteins to enzymatically degrade the capsular outer layer of their hosts, at the initial step of a tightly programmed phage infection process. Host growth conditions also influence the ability of the phage to attach and invade them. Myovirus bacteriophages use a hypodermic syringe -like motion to inject their genetic material into the cell.
After contacting the appropriate receptor, the tail fibers flex to bring the base plate closer to the surface of the cell. This is known as reversible binding. Once attached completely, irreversible binding is initiated and the tail contracts, possibly with the help of ATP , present in the tail,  injecting genetic material through the bacterial membrane.
The injection is accomplished through a sort of bending motion in the shaft by going to the side, contracting closer to the cell and pushing back up. Podoviruses lack an elongated tail sheath like that of a myovirus, so instead, they use their small, tooth-like tail fibers enzymatically to degrade a portion of the cell membrane before inserting their genetic material.
Within minutes, bacterial ribosomes start translating viral mRNA into protein. The host's normal synthesis of proteins and nucleic acids is disrupted, and it is forced to manufacture viral products instead. These products go on to become part of new virions within the cell, helper proteins that contribute to the assemblage of new virions, or proteins involved in cell lysis.
In , Walter Fiers University of Ghent , Belgium was the first to establish the complete nucleotide sequence of a gene and in , of the viral genome of bacteriophage MS2. In the case of the T4 phage , the construction of new virus particles involves the assistance of helper proteins. The base plates are assembled first, with the tails being built upon them afterward.
The head capsids, constructed separately, will spontaneously assemble with the tails. The DNA is packed efficiently within the heads. The whole process takes about 15 minutes. Phages may be released via cell lysis, by extrusion, or, in a few cases, by budding. Lysis, by tailed phages, is achieved by an enzyme called endolysin , which attacks and breaks down the cell wall peptidoglycan. An altogether different phage type, the filamentous phage , make the host cell continually secrete new virus particles.
Released virions are described as free, and, unless defective, are capable of infecting a new bacterium. Budding is associated with certain Mycoplasma phages. In contrast to virion release, phages displaying a lysogenic cycle do not kill the host but, rather, become long-term residents as prophage.
Arbitrium is the name given to this protein by the researchers who discovered it. Given the millions of different phages in the environment, phage genomes come in a variety of forms and sizes.
RNA phage such as MS2 have the smallest genomes, of only a few kilobases. However, some DNA phage such as T4 may have large genomes with hundreds of genes; the size and shape of the capsid varies along with the size of the genome. Bacteriophage genomes can be highly mosaic , i. These modules may be found in other phage species in different arrangements.
Mycobacteriophages , bacteriophages with mycobacterial hosts, have provided excellent examples of this mosaicism.
In these mycobacteriophages, genetic assortment may be the result of repeated instances of site-specific recombination and illegitimate recombination the result of phage genome acquisition of bacterial host genetic sequences. Phages often have dramatic effects on their hosts. As a consequence, the transcription pattern of the infected bacterium may change considerably. Many of these effects are probably indirect, hence the challenge becomes to identify the direct interactions among bacteria and phage.
Several attempts have been made to map protein—protein interactions among phage and their host. For instance, bacteriophage lambda was found to interact with its host, E. However, a large-scale study revealed 62 interactions, most of which were new. Again, the significance of many of these interactions remains unclear, but these studies suggest that there most likely are several key interactions and many indirect interactions whose role remains uncharacterized.
Metagenomics has allowed the in-water detection of bacteriophages that was not possible previously.
Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome , and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes e. MS2 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. It is estimated there are more than 10 31 bacteriophages on the planet, more than every other organism on Earth, including bacteria, combined. Phages have been used since the late 19th century as an alternative to antibiotics in the former Soviet Union and Central Europe, as well as in France.
Escherichia virus T4 is a species of bacteriophages that infect Escherichia coli bacteria. T4 is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle. The species was formerly named T-even bacteriophage , a name which also encompasses includes among other strains or isolates including Enterobacteria phage T2 , Enterobacteria phage T4 and Enterobacteria phage T6. Bacteriophage means to "eat bacteria", and phages are well known for being obligate intracellular parasites that reproduce within the host cell and are released when the host is destroyed by lysis. Containing about genes , these virulent viruses are among the largest, most complex viruses that are known and one of the best studied model organisms.
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