CRISPR is an adaptive immune system used by bacteria to prevent infection by viruses. With CRISPR, bacteria use small pieces of virus DNA to target and destroy invaders, but the viruses can overcome it by mutation. This mutation allows them to re-infect bacterial cells. This interaction can theoretically lead to coevolution, where two organisms change over time in response to each other. Coevolution is thought to be a key driver behind the coexistence of hosts and their pathogens in all organisms.

In this paper, we used a CRISPR bacteria called Streptococcus thermophilus and its virus to look for coevolution in real-time. We show that CRISPR-mediated resistance and virus infectivity followed what is called an Arms Race Dynamic, where hosts and pathogens become more resistant and infective as they coevolve. We confirmed that this Arms Race is driven by simple changes to the DNA of the bacteria and virus. This study provides further insight into the way CRISPR systems shape the ecology and evolution dynamics of bacteria–virus interactions.

Jack Common, SWBio DTP student

Paper: CRISPR-Cas immunity leads to a coevolutionary arms race between Streptococcus thermophilus and lytic phage by J Common, D Morley, ER Westra and S van Houte in Philosophical Transactions B.