Phage inducible chromosomal minimalist island (PICMI), a family of satellites of marine virulent phages

Phage satellites are genetic elements that hijack the phage machinery for their own dissemination. However, only few phage satellites have been characterized, and mechanisms by which they influence microbial evolution in nature are unclear. Here we identify a new family of satellites, the Phage Inducible Chromosomal Minimalist Island (PICMI), which is broadly distributed in the marine bacteria Vibrionaceae. PICMI is characterized by reduced gene content, does not encode genes for capsid remodeling and packages its DNA as a concatemer. PICMI is integrated in the bacterial host genome at the end of the fis regulator and encodes three core proteins necessary for excision and replication. PICMI is dependent on virulent phage particles to spread to other bacteria and confers host protection from other competitive phages, without interfering with its helper phage. The discovery of PICMI strongly suggests that phages, including virulent ones, play important roles for mobility of phage defense elements.