Abstract
Bacterial genomes contain a surprisingly large number of toxin systems that are neutralized by specific cognate antitoxins or immunity factors. Their high abundance is even apparent in common Escherichia coli K12 cloning strains, which contain at least 36 toxin-antitoxin systems, while other bacteria frequently contain more. These numbers raise two key questions: why are they so numerous, and to what extent do toxin systems interact or interfere with one another? Recently in mBio, Wang and co-workers addressed these questions in the social bacterium Myxococcus xanthus, where they investigated crosstalk between four homologous toxin-immunity loci involved in kin discrimination. Here, the type VI secretion system delivers toxins into neighboring myxobacterial cells (F. Wang, J. Luo, Z. Zhang, Y. Liu, et al., mBio e03902-24, 2025, https://doi.org/10.1128/mbio.03902-24). If the target cell is clonal and expresses a complete set of cognate immunity proteins-which are not themselves transferred-the cell is protected. However, if immunity is incomplete, the cell is poisoned.