Bacteriophage - Wikipedia
The lysogenic cycle: The phage infects a bacterium and inserts its DNA into the bacterial chromosome, allowing the phage DNA (now called a prophage) to be. Studies on the Relationship Between Bacteriophage and Bacterial Host Cell. I. Adsorption of Phage by Resistant Variants of Staphylococcus. Jane E. Henry and . A bacteriophage is a type of virus that infects bacteria. In fact, the word " bacteriophage" literally means "bacteria eater," because bacteriophages destroy their.
Myovirus bacteriophages use a hypodermic syringe -like motion to inject their genetic material into the cell. After making contact with 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 done 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 similar to that of a myovirus, so they instead use their small, tooth-like tail fibers enzymatically to degrade a portion of the cell membrane before inserting their genetic material. Synthesis of proteins and nucleic acid[ edit ] Within minutes, bacterial ribosomes start translating viral mRNA into protein.
These products go on to become part of new virions within the cell, helper proteins that help assemble the new virions, or proteins involved in cell lysis. Walter Fiers University of GhentBelgium was the first to establish the complete nucleotide sequence of a gene and of the viral genome of bacteriophage MS2 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. Diagram of a typical tailed bacteriophage structure Release of virions[ edit ] Phages may be released via cell lysis, by extrusion, or, in a few cases, by budding.
What are bacteriophages (phages) and how do they work?
Lysis, by tailed phages, is achieved by an enzyme called endolysinwhich attacks and breaks down the cell wall peptidoglycan. An altogether different phage type, the filamentous phagesmake 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. Genome structure[ edit ] Given the millions of different phages in the environment, phages' genomes come in a variety of forms and sizes.
Bacteriophages in Human Disease: Friends and Foes | sport-statistik.info
RNA phage such as MS2 have the smallest genomes of only a few kilobases. However, some DNA phages 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.
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. Friends and Foes Electron micrograph E. What students may not be aware of is the role bacteriophages play in human disease.
Bacteriophages play a critical role in some human diseases You would not expect bacteria viruses to have an effect on human beings, but a closer look reveals that bacteriophages phages can play a critical role in human disease.
The relationship between phages and human disease is complex. Some of the diseases that have long plagued human beings are indirectly caused by phages.
However, phages can also work to our benefit. There is a history of people using bacteriophages to treat human bacterial infections, which with the advent of increasing bacterial antibiotic resistance, is being more widely explored. Basic phage biology Understanding the role of phages in human disease requires familiarity with some basic phage biology.
The phage particle consists of the phage genome packaged in a capsid. The capsid is a container comprised of phage proteins. Phages have several different types of infectious cycles, two of which are the lytic and the lysogenic life cycles. During a lytic infection, a phage infects a bacterium and takes over its machinery to replicate itself and produce new phage particles.
In the course of replication and release of the new phage particles, the host bacterium is lysed, and thus killed. Phages that can only carry out this type of infection are called lytic, or virulent, phages. Phages can also carry out a lysogenic infection in which the phage inserts its genome into the bacterial genome. Once inserted, the phage genome then remains in the bacterial genome until it receives an environmental signal, causing it to excise itself from the bacterial genome, replicate, and produce viral particles.
Bacteria vs. Bacteriophages: Parallel Evolution of Immune Arsenals
Phages that set up a lysogenic infection are referred to as lysogenic, or temperate, phages. Phages can acquire non-phage genes During either type of life cycle, phages may acquire genes not originally part of their genome.
This process, referred to as transduction, can occur as a result of a lytic or lysogenic infection. During the lytic life cycle, a piece of bacterial DNA may be packaged into the phage particle in place of the phage genome. The resulting particle is no longer capable of replicating itself, but is capable of infecting a new bacterium. When the phage particle infects a new bacterium, the packaged DNA from the original host bacterium is introduced into the new bacterium.
Transduction can also occur as part of a lysogenic life cycle. When a lysogenic phage genome integrated into a bacterial genome pops back out to replicate, bacterial DNA that is adjacent to the phage genome may also be excised. Such bacterial DNA becomes part of the phage genome and is packaged into the phage particle.
In this way, phages can introduce a gene that is harmful to humans e. Among the giant numbers of bacterial cells at a certain habitat a statistical number of bacterial mutations can lead to phage-resistant bacteria. As a consequence, the phages will further be able to attack the bacteria. In natural environments, such a competition between bacteria and phages is mostly of scientific interest. But, if the focus of interest is phage application or phage therapy in order to fight against a dense bacterial colonization, attention is drawn to these specific bacteria and a suitable phage: In such cases, the bacterial numbers are often an extreme challenge for the human immune system that in the worst case collapses: There are many different kinds of antibiotics, they can be allocated to some well-defined chemical substance classes.
Antibiotics are more or less specific against bacteria, but never specific for a certain bacterial species and even less against certain strains of a certain species. This is in contrast to phages that attack almost always only one bacterial species and more typically, only few strains of a species.