T7 Bacteriophage

Legend. Image credit: Wikipedia.

Classification

Viruses; Duplodnaviria; Heunggongvirae; Uroviricota; Caudoviricetes; Autographiviridae; Studiervirinae; Teseptimavirus [Others may be used. Use NCBI link to find]

Species

NCBI: [1]

Teseptimavirus T7

Description and Significance

Like other viruses, the T7 bacteriophage does not produce its own energy. Instead, it infiltrates a bacterium via a membrane protein, and alters the genome in the nuclear envelope. By doing this, the T7 bacteriophage interferes with the protein synthesis and metabolic pathways of the bacteria into producing viral proteins and packaging them with the viruses genome. This phages primary target is bacteria of the Enterobacteriaceae family, with this virus being the biggest killer of E coli.

Genome Structure

The genome of the T7 Bacteriophage is comprised of approximately 40,000 bp of DNA coding for 55 proteins. Many of these genes are overlapping and are removed via refactoring of the genome.

Cell Structure, Metabolism and Life Cycle

The T7 Bacteriophage possesses an icosahedral capsid shell made by gene product 10, and a 12-fold portal, a feature commonly found in tailed bacteriophages and herpesviruses. (Chen, Xiao, Wang, Cheng 2021) The T7 bacteriophage has a tail with a 12-fold adaptor protein gp11 assembly, a sixfold nozzle protein gp12 assembly, and six subunits of trimeric tail fiber gp17. The tail fibers of the T7 bacteriophage are used to recognize potential hosts, and absorb into them. On top of the portal, the hollow capsid shell can be found.

The life cycle of a T7 bacteriophage consists of three primary steps. Firstly, the phage searches for and absorbs into a host; in the second step, the phage transfers its linear DNA genome into a host cell and expresses its phage genes. Third, the host cell is lysed and releases the newly assembled phages. (Nguyen, Kang 2014) On the surface, the T7 bacteriophage targets a lipopolysaccharide receptor, which binds to the C-terminal end of the T7 tail fiber protein. (Nguyen, Kang 2014) The DNA of the phage is translocated into the host in a process dependent on transcription, which is performed by the hosts RNA polymerase and then by the T7 phages RNA polymerase.

Ecology and Pathogenesis

The T7 Bacteriophage inhabits everywhere the Enterobacteriaceae family can be found. The T7 Bacteriophage is a small intracellular parasite that uses its tail and tail fiber proteins to recognize potential hosts. (Holtzman et al 2020) The target of this virus is any bacteria found in the Enterobacteriaceae family, which includes E coli, Salmonella, and Escherichia. Phages and bacteria exert never-ending mutual selection pressure in a never-ending molecular arms race. (Holtzman et al 2020) Bacteriophages and bacteria are thus constantly co-evolving with one another, resulting in ever-changing genetics, proteins, and behaviors, which exemplifies natural selection and survival of the fittest.

The T7 Bacteriophage uses its tail proteins to identify potential hosts, which includes Enterobacteria. Afterwards, it infiltrates the host cell via absorption through attachment sites. After this, the phage penetrates the membrane barrier. The bacteriophage then makes its way to the nuclear envelope of the bacterium and inserts its own dsDNA, altering the bacterium's DNA to create viral proteins and assemble new bacteriophages. Once the new Bacteriophages are assembled, cell lysis begins, and the newly made phages are released, killing the cell.

References

Chen, W., Xiao, H., Wang, L., & Cheng, L. (2021, September 9). Structural changes in bacteriophage T7 upon receptor-induced ... - PNAS. PNAS. https://www.pnas.org/doi/full/10.1073/pnas.2102003118

Holtzman, T., Globus, R., Molshanski-Mor, S., Ben-Shem, A., Yosef, I., & Qimron, U. (2020, January 15). A continuous evolution system for contracting the host range of bacteriophage T7. Nature News. https://www.nature.com/articles/s41598-019-57221-0

Nguyen, H. M., & Kang, C. (2014, February). Lysis delay and burst shrinkage of coliphage T7 by deletion of Terminator Tφ reversed by deletion of early genes. Journal of virology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3911561/#:~:text=The%20replication%20cycle%20of%20phage,release%20newly%20assembled%20phage%20progenies.

U.S. National Library of Medicine. (n.d.). Taxonomy browser (escherichia phage T7). National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=10760&lvl=3&lin=f&keep=1&srchmode=1&unlock

Author

Page authored by Zachary Lovvorn, student of Prof. Bradley Tolar at UNC Wilmington.