Bacterial Immune Systems: to See the Virus and Die

Bacterial immune systems can protect cells at different steps of viral infection, by preventing virus binding and genome injection, destroying viral nucleic acids, disrupting virus replication or assembly of viral particles. Recent studies have shown that along with systems that directly attack invader elements, there are many defense systems that induce the death of the infected cell, thus preventing the spread of viruses and plasmids in the population. The key event in the activation of various immune systems is the recognition of invader elements during infection. Two types of defense systems, CRISPR-Cas and Argonautte proteins, can directly recognize and cleave viral DNA or RNA using short complementary guide oligonucleotides. At the same time, recently discovered new groups of Argonautes can induce suicidal cell response and cause abortive infection. In this case, guided recognition of viral or plasmid targets leads to the activation of additional effector proteins that disrupt cellular metabolism, destroy the cell membrane, or cause nonspecific degradation of cellular and viral DNA. Such systems are important participants in the evolutionary race between viruses and bacteria and can serve as tools for genetic engineering and biotechnology.