The contribution of abortive infection to preventing populations ofLactococcus lactisfrom succumbing to infections with bacteriophage

Abstract

AbstractIn the dairy industry bacteriophage (phage) contamination significantly impairs the production and quality of products like yogurt and cheese. To combat this issue, the strains of bacteria used as starter cultures possess mechanisms that make them resistant to phage infection, such as envelope resistance, or processes that render them immune to phage infection, such as restriction-modification and CRISPR-Cas.Lactococcus lactis, used to manufacture cheese and other dairy products, can also block the reproduction of infecting phages by abortive infection (Abi), a process in which phage-infected cells die before the phage replicate. We employ mathematical-computer simulation models and experiments with twoLactococcus lactisstrains and two lytic phages to investigate the conditions under which Abi can limit the proliferation of phages inL. lactispopulations and prevent the extinction of their populations by these viruses. According to our model, if Abi is almost perfect and there are no other populations of bacteria capable of supporting the replication of theL. lactisphages, Abi can protect bacterial populations from succumbing to infections with these viruses. This prediction is supported by the results of our experiment, which indicate that Abi can help protectL. lactispopulations from extinction by lytic phage infections. However, our results also predict abortive infection is only one element ofL. lactisdefenses against phage infection. Mutant phages that can circumvent the Abi systems of these bacteria emerge. The survival ofL. lactispopulations then depends on the evolution of envelope mutants that are resistant to the evolved host-range phage.