Protection of bacteriophage-sensitive Escherichia coli by lysogens

Bacteriophage λ is a temperate virus infecting the bacterium Escherichia coli. Temperate phages have the ability to form lysogens where the prophage is maintained in the infected bacterium in a largely quiescent state. The lysogen becomes immune to superinfection by λ by blocking the development of the superinfecting phage. Here we report the λ lysogen not only protected itself from killing by λ phages but also protected λ-sensitive bacteria in mixed culture. This protection required that the lysogen was able to adsorb the superinfecting λ phages. The protection was also sensitive to the growth state of the mixed culture, and the λ lysogen lost efficiency in protecting λ-sensitive bacteria as it stopped growing. A mutant of the λ tail protein, λJ, was not subject to this loss of protection. Adsorption of λ having the wild-type J protein but not the mutant λJ protein to E. coli was inhibited by interference with bacterial energy metabolism. The last observation suggests wild-type λ preferentially infects bacteria with competent energy metabolism.