Bacteriophages

Abstract Bacteriophages (phages) are viruses that infect most, if not all, bacteria in the domains Bacteria (eubacteria) and Archaea (archaebacteria). Most (96%) phages have tailed phage morphology, with the rest having a polyhedral, filamentous or pleomorphic morphology. Phage genomes are a single‐ or double‐stranded, linear or circular, deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) molecule. An exception is the cystovirus genome, which consists of three RNA molecules. Most phages produce a lytic infection, which typically involves phage attachment to the cell surface, injection of phage nucleic acid into the cell, intracellular expression of phage genes to produce nascent phage nucleic acid and proteins, assembly of progeny phages, and cell lysis to release progeny phages. In some situations, instead of a lytic infection, some phages remain latent in infected cells – a process called lysogeny. As bacterial predators, phages affect global biogeochemical cycles. Key Concepts: Bacteriophages (phages) are viruses that infect most, if not all, bacteria in the domains Bacteria (eubacteria) and Archaea (archaebacteria). Most (96%) phages have tailed phage morphology, with the rest being polyhedral, filamentous or pleomorphic. Phages genomes are a single‐ or double‐stranded, linear or circular, DNA or RNA molecule, except cystoviruses, which have a genome of three molecules of linear double‐stranded RNA. Most phages have a lytic infection cycle, in which an infected cell produces nascent phage nucleic acid and proteins, which are assembled into progeny phages and released by cell lysis. Some phage infections are lysogenic, in which the intracellular phage remains latent and the cell continues to grow. Bacteria have a type of adaptive immunity, the CPISPR system, against phages and plasmids. As bacterial predators, phages affect global biogeochemical cycles.