A bacteriophage is a virus that infects bacteria. These “bacteria eaters,” often shortened to “phages,” are among the most abundant biological entities on Earth, playing a significant role in microbial ecosystems. Bacteriophage T1 is a well-studied example, and research into its biology has helped illuminate fundamental processes in molecular biology and genetics.
Understanding Bacteriophage T1
Bacteriophage T1 targets Escherichia coli (E. coli) bacteria. Classified as a double-stranded DNA (dsDNA) virus, it was historically placed within the Myoviridae family due to its distinct morphology. Viruses in this former family, now referred to as myoviruses, possess a head-tail structure.
The T1 phage has a distinctive structure, featuring an icosahedral (20-sided) head that encapsulates its genetic material. Connected to the head is a tail, made up of a central tube surrounded by a contractile sheath. The tail also includes a base plate with tail fibers at its distal end, used for attachment to bacterial cells. This highly specific design means T1 primarily infects E. coli and certain Shigella species.
How T1 Interacts with Bacteria
Bacteriophage T1 follows a lytic life cycle, infecting a bacterial cell and ultimately causing its destruction to release new phage particles. The process begins with attachment, where the phage binds to specific receptors on the surface of the E. coli cell, often using its tail fibers. This highly specific binding ensures the phage targets its appropriate host.
Following attachment, the phage injects its genetic material into the bacterium. The protein coat remains outside the bacterial cell. Once inside, the phage’s DNA takes over the bacterial cell’s machinery, redirecting it to produce more phage components. This hijacking of the host’s cellular machinery is a rapid process.
New phage particles then self-assemble within the bacterial cell. In the final step, phages produce enzymes that weaken and break down the bacterial cell wall. This causes the bacterium to burst, a process called lysis, releasing hundreds of new phage particles into the environment. Infection to lysis for T1 typically takes 15-20 minutes.
The Scientific Significance of T1
Bacteriophage T1 has been a valuable model organism in molecular biology and genetics research. Its early studies, notably the 1943 fluctuation test by Salvador Luria and Max Delbrück, demonstrated that bacterial resistance to phages arises from spontaneous mutations, not direct adaptation to the environment. This work contributed to a deeper understanding of genetic recombination and mutation processes.
T1 continues to serve as a research tool, used to study bacterial genetics, including gene transfer mechanisms. Its ability to invade and lyse E. coli strains has led to the development and widespread use of T1-resistant E. coli strains in laboratories. This resistance mechanism involves mutations in the tonA gene, which encodes the outer membrane receptor FhuA that T1 uses for entry.
Studying T1 has also provided insights into how bacteria evolve resistance mechanisms against viral infections. This understanding has broader implications for addressing antibiotic resistance. Furthermore, T1 contributes to the growing field of “phage therapy,” which explores the use of bacteriophages to treat bacterial infections. This offers a potential alternative or supplement to traditional antibiotics, especially against multi-drug resistant bacterial strains.