What is the process of bacterial DNA transfer via a virus called?

The process of bacterial DNA transfer via a virus is called transduction. In this form of horizontal gene transfer, a bacteriophage— a virus that infects bacteria—carries genetic material from one bacterial cell to another.

Transduction can happen when a phage accidentally packages bacterial DNA inside its protein coat. After infecting a new cell, the phage delivers that DNA, which may be broken down, maintained as a plasmid, or incorporated into the recipient chromosome through recombination. Because the DNA travels inside a virus particle, the donor and recipient bacteria do not need to touch.

Scientists usually distinguish generalized and specialized transduction. Generalized transduction can transfer almost any bacterial gene by random packaging during the lytic cycle. Specialized transduction transfers only genes near a prophage's integration site, usually after the prophage is removed incorrectly. A newer category, lateral transduction, has also been described in Staphylococcus aureus.

Transduction is easy to confuse with conjugation and transformation. Conjugation uses direct cell-to-cell contact, while transformation involves uptake of free DNA from the environment. The phenomenon was discovered in Salmonella by Norton Zinder and Joshua Lederberg in 1952.