Chimeric infective particles expand species boundaries in phage-inducible chromosomal island mobilization

Some mobile genetic elements spread among unrelated bacterial species through unknown mechanisms. Recently, we discovered that identical capsid-forming phage-inducible chromosomal islands (cf-PICIs), a new family of phage satellites, are present across multiple species and genera, raising questions about their widespread dissemination. Here, we have identified and characterized a new biological entity enabling this transfer. Unlike other satellites, cf-PICIs produce their own capsids and package their DNA, relying solely on phage tails for transfer. cf-PICIs release non-infective, tailless capsids containing their DNA into the environment. These subcellular entities then interact with phage tails from various species, forming chimeric particles that inject DNA into different bacterial species depending on the tail present. Additionally, we elucidated the structure of the tailless cf-PICIs and the mechanism behind their unique capsid formation. Our findings illuminate the mechanisms used by satellites to spread in nature, contributing to bacterial evolution and the emergence of new pathogens.