Table of Contents
- Introduction
- Classification
- Properties
- Process of Infection
- Reproduction and Life Cycle
- Future Applications
- Frequently Asked Questions
Introduction
Escherichia virus T4 is one of the seven E.coli phages (T1-T7) that belongs to the Myoviridae family. It has a double-stranded DNA, and it was considered as a model organism back in the 1940s, continuing even today. The ‘T-even’ phages, meaning T2, T4 and T6, are similar in structure, genetics and antigenic response.
Classification
Unranked | Virus |
Kingdom | Heunggongvirae |
Phylum | Uroviricota |
Class | Caudoviricetes |
Order | Caudovirales |
Family | Myoviridae |
Genus | Tequatrovirus |
Species | Escherichia virus T4 |
Properties
Genome
- The double helical DNA genome is almost 169 kbp long and encodes 289 proteins.
- The genome is terminally redundant and possesses intron sequences like eukaryotes.
- The DNA undergoes replication by a rolling circle mechanism.
- In the Shine-Dalgarno sequence, GGAG is found abundantly in the early T4 genes.
- The DNA genome is packed in an icosahedral head that is known as a capsid.
- This virus can only undergo a lytic life cycle, not the lysogenic life cycle.
Structure
- The T4 bacteriophage belongs to the order Caudovirales because it possesses a contractile tail.
- A T4 bacteriophage is made up of a head, a tail and long tail fibres (LTFs) that are assembled independently before forming a mature phage.
- It is a large virus sizing approximately 90 nm wide and 200 nm long.
- The tail of the phage is hollow for easy transmission of the nucleic acid to the host cell.
- The head of a mature phage is 1150 Å long and 850 Å wide, which encapsulates the genome.
- The head is attached to a contractile head that is about 925 Å long and 240 Å in diameter.
- A hexagonal base plate that is 270 Å high and 520 Å in diameter is attached to the distal end of the contractile tail.
- The LTFs are 1450 Å long and attached to the periphery of the hexagonal baseplate. They are six in number.
- The LTFs are sensors that recognise the receptor molecules on the host.
- Additionally, there are six short tail fibres (STFs) that are attached beneath the baseplate. They unfold upon recognition with the host and increase the efficiency of the infection.
Process of Infection
The Escherichia virus T4 phage initiates infection by binding to the porin proteins and lipopolysaccharides on the surface of the E.coli cells with their long tail fibres. This initiates a recognition signal that is sent from the LTFs to the baseplate, and as a result, the short tail fibres unravel and attach themselves irreversibly to the cell surface of E.coli. Next, the baseplate changes confirmation and the tail sheath contracts to drill a puncture into the outer membrane of the bacteria.
Lysozyme enzymes from the tail are activated, and they destroy the peptidoglycan layer of the bacteria. The remaining membranes are also degraded, and then the viral genome is transferred from the head of the virus via the tail into E.coli cells.
Reproduction and Life Cycle
As stated above, the Escherichia virus T4 undergoes only a lytic life cycle. The lytic life cycle can be defined as the lysis of the host cell and release of the new viral progenies. As soon as the bacteriophages enter the host cell, they take over the machinery of the host cell and start to multiply rapidly.
The phage progeny multiplies to reach a certain number, after which the host cell bursts. The T4 phage has a burst size of almost 150 viral particles. The whole process of the infection and lysis of cells can be understood in five stages:
- Adsorption and penetration
- Arrest of the host gene expression
- Synthesis of enzymes
- DNA replication
- Formation of new viral particles.
The lytic life cycle takes place in a time span of 30 minutes at 37 ℃.
Future Applications
The complete genome of the T4 phage was sequenced in 2003. The amount of molecular information of the phage in hand could be used for medical advancements such as vaccine development, gene therapy, antibiotic agents and targeting the malfunctioning cells.
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Also Read:
- Structure and Life Cycle of Bacteriophage
- Difference between Lytic and Lysogenic Cycle
- Virus Life Cycle: Introduction, Life Cycle, FAQs
Frequently Asked Questions
Q1
What does Escherichia virus T4 do?
The Escherichia virus T4 is a bacteriophage belonging to the Myoviridae family that only infects the E.coli bacteria.
Q2
Are bacteriophages harmful to humans?
Bacteriophages are categories of viruses that infect only bacteria. They are harmless to humans.
FAQs
As stated above, the Escherichia virus T4 undergoes only a lytic life cycle. The lytic life cycle can be defined as the lysis of the host cell and release of the new viral progenies. As soon as the bacteriophages enter the host cell, they take over the machinery of the host cell and start to multiply rapidly.
Is T4 bacteriophage good or bad? ›
Bacteriophages (phages) are viruses that infect bacterial cells. Example: T4 and T2 bacteriophage. Bacteriophages are not bad. They are extremely beneficial in many ways.
What bacteria does T4 infect? ›
Escherichia virus T4 is a species of bacteriophages that infect Escherichia coli bacteria. It is a double-stranded DNA virus in the subfamily Tevenvirinae from the family Myoviridae. T4 is capable of undergoing only a lytic life cycle and not the lysogenic life cycle.
What is the structure of the T4 virus? ›
T4 assembly is divided into three independent pathways: the head, the tail and the long tail fibers. The prolate head encapsidates a 172 kbp concatemeric dsDNA genome. The 925 Å-long tail is surrounded by the contractile sheath and ends with a hexagonal baseplate.
What impact did the cell life cycle have on bacteriophage T4 infection? ›
The cell cycle had a significant impact on the outcome of infection. Cell burst size was smallest for newly formed cells and increased dramatically as these progressed in the cell cycle.
What is the stage of virus life cycle? ›
The viral life cycle can be divided into several major stages: attachment, entry, uncoating, replication, maturation, and release. On this page: Viral attachment to host cell. Viral entry.
Can bacteriophages help humans? ›
Bacteriophages play a critical role in some human diseases
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.
Can bacteriophages walk? ›
Repeating these dynamic processes allows the T4 phage to randomly walk across the bacterial surface to search for an optimal site before committing to infection.
Can bacteriophages be used as antibiotics? ›
Bacteriophages (BPs) are viruses that can infect and kill bacteria without any negative effect on human or animal cells. For this reason, it is supposed that they can be used, alone or in combination with antibiotics, to treat bacterial infections.
How is the T4 virus able to penetrate the cell wall of E. coli? ›
The sequence of events that lead to bacterial infection by T4 is also known (3, 7). It starts with the virus finding and binding the corresponding receptors on the host cell. After the strong contact is established, the cellular membrane is pierced and the viral DNA is eventually ejected into the host cell.
T4 infection of exponentially growing E. coli quickly disrupts host genome structure and expression, largely by making use of T4's complete substitution of HMdC for dC in its DNA (Kutter et al., 1994c). Elongation of transcription of all cytosine-containing DNA is terminated and host DNA replication is disrupted.
What is the cause of E. coli infection? ›
You may be exposed to E. coli from contaminated water or food — especially raw vegetables and undercooked ground beef. Healthy adults usually recover from infection with E. coli O157:H7 within a week.
What is the life cycle of the T4 virus? ›
Lytic life cycle is the process where a phage enters into the host, takes over their replication machinery and destroys the host cell to complete their life cycle. In T4 bacteriophages, the lytic cycle takes place at a temperature of 37℃ in about 30 minutes.
Does T4 bacteriophage have DNA? ›
Electron micrographs of bacteriophage T4. The well-recognized T4 morphology was nature's prototype of the NASA lunar excursion module. (A) Extended tail fibers recognize the bacterial envelope, and its prolate icosahedral head contains the 168,903-bp dsDNA genome.
Are viruses considered to be alive? ›
Most biologists say no. Viruses are not made out of cells, they can't keep themselves in a stable state, they don't grow, and they can't make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.
What is the lytic cycle of a T4 phage? ›
In T4 bacteriophages, the lytic cycle takes place at a temperature of 37℃ in about 30 minutes. The T4 bacteriophage enters the host and starts dividing into progeny phages at a fast rate. Once they reach a certain number of progeny phages, the host cell is lysed and the phages are released for infecting new host cells.
What are the stages of the E. coli life cycle? ›
In the life cycle of a bacterium there are several key processes: cellular growth, chromosome replication and decatenation, nucleoid partition, septum formation, and cell division.
Is T4 lysogenic? ›
T4 is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle. The T4 Phage initiates an E. coli infection by recognizing cell surface receptors of the host with its long tail fibers (LTF).
What type of viral life cycles is displayed by the T4 bacteriophage? ›
Bacteriophage T4 is a large, tailed, double-stranded DNA (dsDNA) virus. This phage has an exclusively lytic lifecycle (Kutter et al. 1995; Karam 1994; Baschong et al.
