Bacterial defense systems: mechanism, homology to eukaryotic immunity, and applications

As a vital component of the microbial world, bacteria are constantly challenged by invasions from mobile genetic elements (MGEs) such as bacteriophages and plasmids. To counteract these threats, bacteria have evolved a rich diversity of defense systems. This review first provides a framework of currently known defense systems based on their mechanisms of functional characteristics and action mode, alongside a synthesis of the fundamental patterns that define how these systems operate. Building on this foundation, we delve into the homology between bacterial defense systems and eukaryotic antiviral immunity, emphasizing how conserved molecular modules, despite independent evolutionary paths, reflect a shared logic underlying immune defense across domains of life. Finally, we summarize the biotechnology tools originating from bacterial defense systems and further introduce their practical applications across practical domains, including molecular diagnostic technologies and precision medicine, trait improvement of crops and livestock, and engineering of fermentation strains. By constructing a systematic framework encompassing mechanisms, evolutionary homology, and applied innovations, this review deepens the overall understanding of bacterial defense systems and provides a foundation for their more effective future utilization.