Joshua Lederberg and his graduate student Norton Zinder showed in 1952 that bacteriophages could transfer genetic information between bacteria in Salmonella. This process explained how bacteria of different species could gain resistance to the same antibiotic very quickly.
Transduction also refers to the process whereby foreign DNA is introduced into another cell via a viral vector. This is a common tool used by molecular biologists to introduce a foreign gene into a host cell's genome.
When bacteriophages infect a bacterial cell, their normal mode of reproduction is to harness the replicational, transcriptional, and translation machinery of the host bacterial cell to make numerous complete viral particles, including the viral DNA or RNA and the protein coat. Errors in this process can result in the virus carrying over DNA from one bacterium to another.