Bacteria are constantly being infected by viruses, or phage. To combat this, many species have evolved a defense mechanism known as CRISPR. This allows a bacterial cell to remember which phages have infected it, so that the next time it encounters that phage, it can destroy the phage and prevent infection. Understanding the battle between CRISPR and phage is important, because many of the bacteria that hurt or help us are contantly challenged by them. These interactions are also a useful model with which to understand more general concepts that affect how diseases spread and change over time.

Using a CRISPR bacteria and its phage, we looked at how repeatedly restricting the genetic diversity of both organisms would affect if phage can survive, and what kind of defense mechanisms the bacteria would evolve. Although we thought that low diversity would help the phage, we found the opposite to be true. Restricting diversity actually helped the bacteria, because bacterial cells became more spread out in space and so harder for phage to find and infect. This effect also had little to do with whether bacteria had CRISPR or not. This paper tells us more about how immune systems and ecology link together to influence the battle between disease-causing organisms, and those that they infect.

Jack Common, SWBio DTP student

Paper:  CRISPR evolution and bacteriophage persistence in the context of population bottlenecks by J Common and E R. Westra in RNA Biology.