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Bacteria have immune systems to detect and defend against mobile genetic elements, such as phages.
The interaction between Gene transfer agents (GTAs) (i.e., domesticated prophages) and bacterial immune systems is not well understood. A study using transposon mutagenesis and deep sequencing in Caulobacter crescentus identified a system called LypABC, crucial for GTA-mediated cell lysis and gene transfer. It is not needed for DNA packaging into GTA particles but is necessary for host cell lysis. The peptidase domains of LypA and LypC, and the ATPase domain of LypB, are involved in this lysis process. Overproduction of LypABC is toxic, requiring regulation by the transcriptional repressor CdxB. CdxB binds to the promoters of lypABC and essential GTA activator genes, linking GTA activation to host cell lysis. The study suggests bacterial immune systems can be adapted to facilitate horizontal gene transfer by GTAs.