Are phages parasites or symbionts of bacteria?

Abstract

Bacteria and phages have co-existed for several billions of years. The direct observation of their relationship, and the evidence that phages cause bacterial lysis and death, has led researchers to believe that phages and bacteria are natural enemies and that phages can be applied as antimicrobial agents. However, phages are also known to provide various benefits for their bacterial hosts, and on many occasions the phage-host interaction resembles a symbiotic relationship. In this chapter, we evaluate findings in different bacterial genera and their associated phages to assess if phages should be considered as bacterial parasites or symbiotic organisms.