Luciano Marraffini studies how CRISPR–Cas systems protect bacteria and archaea against infection by viruses and other pathogens. Marraffini and his team use molecular genetic techniques to investigate the mechanisms behind these prokaryotic immune systems. In particular, they are focused on how snippets of a pathogen’s DNA are captured and integrated into the bacterial genome to create a memory of an infection. The team is also characterizing and comparing the different subtypes of CRISPR–Cas systems – few of which have been studied in detail – with the goal of better understanding the evolutionary significance of this diversity.