How a Bacterial Immune System Became Gene Editing
Yogurt-makers found it first, in 2007, fighting off the viruses that were ruining their cultures.
In the late 1980s, a Japanese researcher named Yoshizumi Ishino noticed strange repeating sequences in the DNA of E. coli, separated by short unique "spacers" that looked like nothing in particular. The pattern showed up in the genomes of half the bacterial species anyone bothered to look at. It got the name CRISPR — clustered regularly interspaced short palindromic repeats — and sat there as a curiosity for nearly twenty years.
The spacers turned out to be trophies. In 2007, microbiologists at the dairy company Danisco showed that the unique segments were copied from viruses that had previously infected the bacteria. CRISPR was a memory bank. When a matching virus showed up again, the cell would transcribe the stored sequence, load it into a protein scissors called Cas9, and cut the invader's DNA at the matching spot. A bacterial immune system, found inside a tank of yogurt cultures.
Jennifer Doudna at Berkeley and Emmanuelle Charpentier in Sweden saw the rest of the story. In a 2012 paper in Science, they showed Cas9 could be reprogrammed: feed it any short guide RNA you wanted, and it would cut DNA at the matching site. You could, in other words, point a molecular knife at a single sequence in a three-billion-letter genome and snip. They shared the 2020 Nobel Prize in Chemistry for it.
The technique is now used to make disease-resistant rice, knock out genes in mice in a single afternoon, and treat sickle-cell anemia in human patients. The first FDA-approved CRISPR therapy, Casgevy, cleared in late 2023. The molecular toolkit started as bacteria fighting bacteriophages. We are now using it on ourselves.
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