Wageningen researchers describe in Science how Type III CRISPR-Cas systems activate a whole cascade of reactions that causes an infected bacterium to die but the rest of the colony to survive. ‘You could call it an altruistic act.’

CRISPR-Cas9 first came to prominence a few years ago as a cut-and-paste tool for DNA. Since then, many other CRISPR-Cas variants have been found, almost all of which do the same thing: cut foreign DNA. But there is one exception: type III CRISPR-Cas from the bacterium Haliangium ochraceum cuts mainly RNA. This makes the system special and strange’, says Raymond Staals, associate professor at Wageningen University. Cutting RNA to defend itself is actually pretty stupid, because viruses can just make new RNA from the original DNA. Nevertheless, it works and it took us a long time to understand why.

Staals has been studying the type III system since 2011, and around 2018 it became clear that the system not only cuts RNA, but also makes certain signalling molecules. ‘Cutting RNA also releases a number of signalling molecules’, Staals continues. ‘This has been known for some time, but our work shows that these signalling molecules trigger a cascade of reactions similar to apoptosis. And that could be of interest in the future.’