Inovirus

Inovirus is a genus of filamentous bacteriophages within the family Inoviridae. These viruses infect bacteria and are characterized by their long, flexible filaments. The best-known members include M13, fd, and f1, which have been widely studied in molecular biology.

Morphology and genome: Inoviruses form non-icosahedral, helical virions that are about 6 to 7 nanometers in diameter and can reach lengths of several hundred nanometers to over a micron. Their genome is a circular single-stranded DNA molecule, typically around 6.5 kilobases, encoding a compact set of genes for coat proteins, a few replication and assembly proteins, and necessary regulatory elements. The major coat protein forms the bulk of the filament, with several minor coat proteins contributing to virion structure.

Replication and life cycle: Inoviruses replicate via a rolling-circle mechanism inside the host cell and assemble at the bacterial inner membrane. Unlike lytic phages, they do not lyse the host cell; mature virions are continuously extruded from the cell while it remains viable and dividing. This results in a chronic, non-lytic infection with persistent virion production.

Host range and ecology: Inoviruses primarily infect Gram-negative bacteria, notably Escherichia coli and related species. They are encountered in laboratory settings and natural environments such as aquatic systems, where they can influence bacterial physiology and horizontal gene transfer dynamics.

Applications and significance: Inoviruses have served as important model systems in virology and molecular biology. Phage display technologies exploit the filamentous coat proteins to present peptides or proteins on virion surfaces, enabling selection and engineering of binding molecules. They are also studied for insights into virus-host interactions and nanomaterial applications.