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The arms race between bacteria and phages led to the emergence of a variety of genetic systems used by bacteria to defend against viral infection, some of which were repurposed as powerful biotechnological tools. While numerous defense systems have been identified in genomic regions termed defense islands, it is believed that many more remain to be discovered. Here, we show that P2- like prophages and their P4-like satellites have genomic hotspots that represent a significant source of novel anti-phage systems. We validate the defense activity of 14 systems spanning various protein domains and describe PARIS, an abortive infection system triggered by a phage-encoded anti-restriction protein. Immunity hotspots are present across prophages of distant bacterial species, highlighting their biological importance in the competition between bacteria and phages.

S U M M A R YThree phages, isolated from soil samples collected in different localities, produced turbid plaques with a characteristic morphology on Streptomyces coeZicoZor ~3 ( 2 ) . Surviving growth from the plaques was lysogenic: when isolated and purified it was resistant to lysis by the homologous phage and released phage at a low frequency during growth. The three phages were homoimmune. The chromosomal attachment site of one of the prophages, VP5, was mapped in a position between hisE and cysD -that is, in a region devoid of standard markers -on the circular linkage map of the host, by crossing defective lysogens with sensitive strains. The host range of VP5 was restricted; only certain strains belonging to the S. coelicolor (S. violaceorkber) group were attacked. VP5 gave rise to clear-plaque mutants, incapable of lysogenizing the host, at a spontaneous frequency of I O -~, which was increased by U.V. irradiation and by hydroxylamine mutagenesis ; the clear-plaque mutants were incapable of lysing strains carrying the wild-type prophage. Electron microscopy showed that VP5 belongs to group B of Bradley's morphological classification.