Inoviruses

Inoviruses, or inoviruses, are a family of filamentous bacteriophages that infect bacteria, particularly Gram-negative species such as Escherichia coli and Vibrio spp. They form long, flexible filaments about 6 nanometers in diameter and can exceed a micrometer in length. The virions are non-lytic and are continuously extruded from the host cell.

Genome and replication: Inoviruses have circular single-stranded DNA genomes, typically about 5–10 kilobases, encoding a small set of genes for the coat proteins and replication. The major coat protein pVIII builds the body of the filament; minor coat proteins pIII, pVI, pVII, and pIX are located at the ends and mediate infection. Replication occurs by rolling-circle mechanisms and the genome is maintained extrachromosomally. Virions exit through the cell envelope without killing the host, causing a chronic infection.

Lifecycle and host interaction: Inoviruses generally do not integrate into the host genome or form lysogens. They rely on attachment to bacterial pili (commonly the F pilus in E. coli) or other surface structures to initiate infection, after which new virions are secreted from the cell.

Applications and biology: Inoviruses are widely used in phage display technologies, in which foreign peptides or proteins are fused to coat proteins such as pIII or pVIII to be presented on the virion surface. They are also used as tools in nanotechnology and as models for studying virus-host interactions.

Taxonomy and ecology: The group is known as Inoviridae, a family of filamentous ssDNA bacteriophages. Inoviruses are found in diverse environments, contributing to horizontal gene transfer and influencing bacterial community dynamics.