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Significance Staphylococcal pathogenicity islands (SaPIs) are highly mobile and carry and disseminate superantigen and other virulence genes. Here we report a remarkable example of molecular parasitism in which the SaPIs hijack the packaging machinery of the phages they victimize, using two unrelated and complementary mechanisms. Phage packaging starts with the recognition in the phage DNA of a specific sequence, termed “ pac ” or “ cos ” depending on the phage type. The SaPI strategies involve carriage of the helper phage pac - or cos -like sequences in the SaPI genome, which ensures SaPI packaging in full-sized phage particles, depending on the helper phage machinery. These strategies interfere with phage reproduction, which ultimately is a critical advantage for the bacterial population by reducing the number of phage particles.
Quiles‐Puchalt et al. (Mon,) studied this question.