Bacterial defense systems: Mechanisms, homology to eukaryotic immune systems, and applications

Bacteria, as fundamental members of the microbial biosphere, are under constant threat from mobile genetic elements (MGEs), including bacteriophages and plasmids. In response, diverse molecular defense strategies have emerged to detect, neutralize, and eliminate these invaders. This review provides a comprehensive framework for categorizing known bacterial defense systems based on mechanistic principles and modes of action, alongside a synthesis of core operational themes that underlie their functional diversity. Particular attention is given to evolutionary parallels between bacterial immunity and antiviral mechanisms in eukaryotes, with emphasis on conserved molecular modules that reflect a convergent logic of immune defense across biological domains. Biotechnology platforms harnessing bacterial defense systems are also examined, with a focus on their application across practical domains, including genetic enhancement of crops and livestock, development of molecular diagnostics and precision therapies, and optimization of microbial strains for industrial fermentation. By integrating mechanistic architecture, evolutionary relationships, and translational advances into a coherent framework, this review broadens the conceptual understanding of bacterial immunity and lays the groundwork for its expanded application in both research and biotechnological innovation.