Bacteriofaagi

Bacteriofaagi, commonly known as bacteriophages or phages, are viruses that infect bacteria. They are diverse in form and genetics and are among the most abundant biological entities on Earth. Phages influence bacterial populations and participate in nutrient cycles across ecosystems.

Structure and genome: Most bacteriophages have a protein capsid enclosing their genetic material, and many are tailed. The tail acts as a device for recognizing and injecting the genome into a bacterial cell. Genome types vary: the majority of well-studied phages contain double-stranded DNA, but some have single-stranded DNA or RNA genomes. Phage morphology ranges from icosahedral heads with tails to filamentous or pleomorphic forms, reflecting multiple viral families.

Life cycles: Phages can follow lytic or lysogenic pathways. In the lytic cycle, infection leads to replication of phage genomes, production of progeny virions, and host cell lysis releasing new phages. In the lysogenic cycle, the phage genome integrates into the bacterial chromosome as a prophage and is replicated with the host; under certain conditions, the prophage can be induced to enter the lytic cycle.

Ecology and applications: Phages mediate horizontal gene transfer through transduction and help shape bacterial communities. They have practical uses in phage therapy to treat antibiotic-resistant infections, in biocontrol to reduce pathogenic bacteria in agriculture and food processing, and as tools in biotechnology, such as phage display and cloning vectors. Bacteria deploy defense systems like CRISPR-C Cas, while phages evolve counter-defense strategies.

History: Bacteriophages were discovered in the late 1910s by Frederick Twort and independently by Félix d'Herelle. Since then, phages have become central to microbiology, ecology, and biotechnology.