JL Weissman

The Battle Between Microbes and Their Viruses


I study the ancient and ongoing battle between microbes and their viral pathogens. Over billions of years of coevolution with their viruses, bacteria and archaea have evolved a broad set of of mechanisms for defending themselves against infection.

For example, the CRISPR adaptive immune system allows microbes to record “memories” of past infection in the form of short viral sequences stored on the host genome:


CRISPR is found in most groups of microbes, but many organisms lack this immune system:


Why? If CRISPR is so great why doesn’t every microbe have it?


I look at how different environments and lifestyles lead to selection for or against particular defense strategies, like CRISPR.