Bacteria encode sophisticated anti-phage systems that are diverse and versatile and display high genetic mobility. How this variability and mobility occurs remains largely unknown. Here, we demonstrate that a widespread family of pathogenicity islands, the phage-inducible chromosomal islands (PICIs), carry an impressive arsenal of defense mechanisms, which can be disseminated intra- and inter-generically by helper phages. These defense systems provide broad immunity, blocking not only phage reproduction, but also plasmid and non-cognate PICI transfer. Our results demonstrate that phages can mobilize PICI-encoded immunity systems to use them against other mobile genetic elements, which compete with the phages for the same bacterial hosts. Therefore, despite the cost, mobilization of PICIs may be beneficial for phages, PICIs, and bacteria in nature. Our results suggest that PICIs are important players controlling horizontal gene transfer and that PICIs and phages establish mutualistic interactions that drive bacterial ecology and evolution.
Sensor:Unknown
Activator:Unknown
Effector:Unknown
contributors:
-Marian Dominguez-Mirazo
relevantAbstracts:
-doi:10.1016/j.cell.2022.07.014
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# FS_HP
## To do
## Description
PICIs (Phage-inducible chromosomal islands) are highly mobile genetic elements that reside in the bacterial chromosome in the absence of a helper phage. Following infection by the helper phage, PICIs excise and replicate by hijacking the helper phage machinery. The FS_HP system was discovered in E. fergusonii through manual search for immune systems in flanking regions of gram-negative PICIs :ref{doi=10.1016/j.cell.2022.07.014}. It is composed by a single protein with a hypothetical domain, from which it derives the HP part of its name. The system showcases a broad defense spectrum. It was tested against 15 lytic phages in 3 gram negative bacteria, and protected the bacterial host against 3 unrelated phages in 2 different bacteria species. FS_HP also blocked the formation of phage particles upon induction of the P22 S. enterica prophage. Therefore, the system can block phage in both lytic and lysogenic life cycles. It was also shown to reduce the production of transducing particles.
## Molecular mechanisms
As far as we are aware, the molecular mechanism is unknown.
