Filamentous Bacteriophages: Biology and Applications

Abstract Filamentous bacteriophages contain a circular single‐stranded deoxyribonucleic acid (ssDNA) genome packaged into long filaments. These phages do not reproduce by lysing bacteria; instead, they are secreted into the environment without killing the host. Well‐studied Escherichia coli K12‐infecting Ff phages (f1, fd or M13) always replicate episomally; however a growing number of ‘lysogenic’ or chromosomally integrated filamentous phages of Gram‐negative bacteria are being discovered. The ‘lysogens’ can be induced; however phage reproduction does not require genome excision from bacterial chromosome and does not lyse the host cells. Some filamentous phages enhance the virulence of their host organisms, the most striking example being the CTXφ of Vibrio cholerae , which encodes cholera toxin. E. coli Ff phages are the workhorse of phage display technology, whose most notable ‘products’ are therapeutic recombinant antibodies. Ff are also being used in nanotechnology as templates for assembly of nanostructures, which has already led to their incorporation into a working nanobattery. Key Concepts: Filamentous bacteriophages are long filaments (6–7 nm×>500 nm) that contain a single‐stranded circular DNA genome. Filamentous bacteriophages replicate via a rolling circle mechanism, one strand at a time. Filamentous bacteriophages do not lyse the cells; they are released by secretion, using a dedicated filamentous phage assembly secretion system. Filamentous phage secretion‐assembly requires the proton‐motive force and ATP. Some filamentous phages replicate exclusively as episomes, while others also integrate their genomes into the host chromosome, forming a lysogen. Induction of the lysogen does not result in cell lysis. Ff filamentous phages of E. coli (f1, M13 and fd) have been used interchangeably as vectors and helper phages in DNA sequencing, as a protein display platform in phage display technology and as a template for assembly of nanostructures in nanotechnology.