A mutation in the methionine aminopeptidase gene provides phage resistance in Streptococcus thermophilus

Abstract

AbstractStreptococcus thermophilusis a lactic acid bacterium widely used by the dairy industry for the manufacture of yogurt and specialty cheeses. It is also a Gram-positive bacterial model to study phage-host interactions. CRISPR-Cas systems are one of the most prevalent phage resistance mechanisms inS.thermophilus. Little information is available about other host factors involved in phage replication in this food-grade streptococcal species. We used the model strainS.thermophilusSMQ-301 and its virulent phage DT1, harboring the anti-CRISPR protein AcrIIA6, to show that a host gene coding for a methionine aminopeptidase (metAP) is necessary for phage DT1 to complete its lytic cycle. A single mutation inmetAPprovidesS.thermophilusSMQ-301 with strong resistance against phage DT1. The mutation impedes a late step of the lytic cycle since phage adsorption, DNA replication, and protein expression were not affected. When the mutated strain was complemented with the wild-type version of the gene, the phage sensitivity phenotype was restored. When this mutation was introduced into otherS.thermophilusstrains it provided resistance againstcos-type (Sfi21dt1virusgenus) phages but replication ofpac-type (Sfi11virusgenus) phages was not affected. The mutation in the gene coding for the MetAP induces amino acid change in a catalytic domain conserved across many bacterial species. Introducing the same mutation inStreptococcus mutansalso provided a phage resistance phenotype, suggesting the wide-ranging importance of the host methionine aminopeptidase in phage replication.