bacteriofagen

Bacteriofagen, commonly referred to as bacteriophage or phage, are viruses that infect bacteria. They are obligate intracellular parasites that require bacterial host cells to replicate. Bacteriophages are highly diverse in genome type and morphology; many known phages have double-stranded DNA and a head–tail structure consisting of an icosahedral capsid attached to a helical tail with tail fibers that recognize bacterial receptors. They are among the most abundant biological entities in many environments, including soil, oceans, and the human gut.

Lifecycle: Phages attach to specific receptors on the bacterial surface, inject their genetic material, and hijack the host's machinery to produce progeny. Lytic phages replicate rapidly and cause cell lysis, releasing new virions. Lysogenic phages can integrate their genome into the host as a prophage, remaining dormant until induction by stress, at which point the phage genome enters the lytic program.

Ecology and evolution: In natural ecosystems, phages influence bacterial population dynamics, drive diversity, and contribute to horizontal gene transfer, notably through transduction. Some phages carry genes that alter bacterial traits, including virulence or antibiotic resistance, though such genes are not universal and transfer depends on context.

Applications and research: Bacteriophages have been studied as models for molecular biology and genetics since the early 20th century. They are explored for therapeutic use in phage therapy to treat bacterial infections, particularly where antibiotics are ineffective. Phages are also used in biotechnology and diagnostics, for example in phage display, bacterial detection, and as vectors or tools in genetic engineering. Safety and regulatory considerations remain important due to host specificity and potential for gene transfer.