DNA Bacteriophages

DNA bacteriophages are viruses that occur in various forms and infect bacteria by injecting their DNA.

They can have either single-stranded DNA called ssDNA, or double-stranded DNA called dsDNA genomes.

For example, the ΦX174 phage, an icosahedral ssDNA phage, has a small genome with overlapping genes. This allows multiple proteins to be encoded through different reading frames.

This phage replicates via rolling circle replication, forming a double-stranded intermediate before generating new genomes.

Finally, the progeny are released via host lysis.

In contrast, M13, a filamentous ssDNA phage, exits the host cell through extrusion rather than lysis, allowing continuous phage production while keeping the host alive.

Among the dsDNA phages, the T7 phage replicates bidirectionally, forming concatemers processed by a terminase enzyme for genome packaging.

On the other hand, Mu initiates replication via transposition, inserting into multiple sites across the host genome. It then excises and packages its linear genome into new virions.