The hidden arsenal: A plasmid-encoded defence system confers resistance against the Bacillus subtilis phage SPβ

As a natural component of the environment, bacteriophages are omnipresent and outperform their hosts in both diversity and abundance. The constant evolutionary arms race leads to the development of many different antiphage defence systems in bacteria and archaea (1). Currently, over 150 different defence systems have been discovered, with ongoing studies likely to uncover new mechanisms or better characterize known ones (2).

In this study, we present a novel plasmid-derived antiphage defence system from Bacillus thuringiensis, which, upon introduction into the prophage-free Bacillus subtilis strain TS01 (3), confers resistance against the temperate phage SPβ c2 (4). The mediated resistance is observed by a decrease in phage titre and an alteration in plaque morphology. The genomic region responsible for conferring resistance, designated as the spbB locus, ensures the stable segregation of the plasmid in B. thuringiensis and Bacillus subtilis (5). The resistance is primarily attributed to spbB and its adjacent region, encompassing a small noncoding RNA of the skipping-rope type (6) and a subsequent intrinsic terminator (5). In the presence of the spbB locus phage propagation or replication is impaired due to cellular death or growth inhibition. This applies not only to phages of the SPβ family but also to B. subtilis phages from other genera.

The defence system outlined in this study represents a previously unrecognized category of antiphage defence that shows no homology to any systems previously described. Studying antiphage defence systems provide further knowledge about phages and phage-host interactions. Furthermore, understanding the diverse defence strategies employed by bacteria against phages can aid in the development of novel antimicrobial therapies (7).

(1) Hampton, H. G., et al. Nature 577, 327–336 (2020).(2) Tesson, F. et al. Nature Communications 13, 2561 (2022).(3) Schilling, T.,et al. Viruses 10, 241–254 (2018).(4) Kohm, K. et al. Nucleic Acids Research 51,9452–9474 (2023).(5) Lereclus, D. & Arantes, O. Molecular Microbiology 6, 35–46 (1992).(6) Weinberg, Z. et al Nucleic Acids Research 45, 10811–10823 (2017).(7) Teklemariam, A. D. et al. Antibiotics 12, 381 (2023).