The CRISPR Origin Story: How Bacteria Gave Us the Gene-Editing Revolution 

Section 1 — The Microbial War That Started Everything

Long before any human being walked the Earth, an invisible war was already being fought. On one side: bacteria, the oldest living organisms on the planet, present for over 3.5 billion years. On the other side: bacteriophages, viruses that prey exclusively on bacteria, and which are the most abundant biological entities on Earth — there are an estimated 10³¹ of them, outnumbering bacteria by perhaps ten to one.

A bacteriophage works like a hypodermic needle with legs. It lands on a bacterial cell, injects its genetic material through the bacterial membrane, and immediately hijacks the bacterium’s entire molecular machinery — its ribosomes, its enzymes, its energy production — forcing it to manufacture hundreds of new virus copies. Within twenty minutes the bacterium bursts open, releasing a fresh wave of phages to infect neighbouring cells. From the bacterium’s perspective, the phage is an existential threat arriving at nanoscale speed.

Bacteria have evolved many defences: thick cell walls, surface receptor mutations that prevent phages from docking, enzymes that chew up foreign DNA. But the most sophisticated defence — the one that would eventually revolutionise medicine — is an adaptive immune memory. Some bacteria, it turns out, can remember a virus they’ve survived. And that memory is written directly into their DNA.

Understanding why evolution would produce such a system — and how it works at the molecular level — is the foundation of everything that follows. Because once scientists understood this bacterial memory system well enough, they realised it could be reprogrammed. And a reprogrammable molecular memory that can recognise any DNA sequence is, with minimal modification, the most powerful gene editing tool ever created.

Section 2 — 1987: The First Clue That Nobody Understood

The story of CRISPR begins not with a grand experiment but with a puzzling footnote in a routine paper. In 1987, a Japanese graduate student named Yoshizumi Ishino at Osaka University was studying a gene in the bacterium Escherichia coli called iap, which codes for an enzyme involved in amino acid metabolism. Completely unremarkable, as bacterial genes go.

While sequencing the DNA around the iap gene, Ishino noticed something odd in the downstream sequence. There was a series of repeated DNA segments — short sequences of about 29 base pairs, showing up again and again, each separated by a unique “spacer” sequence of about 32 base pairs. The repeating sequences were nearly identical each time. The spacers between them were all different.

Ishino reported this as an oddity in a brief footnote of his paper, noting that the “presence of such a structure is a noteworthy feature.” He had no idea what it meant. Nobody did. The paper was published, filed away, and largely forgotten. At the time, the molecular biology community had far more exciting things to think about.

This is a crucial moment in the history of science. One of the most important structures in all of biology was sitting in plain sight in a published paper — and the entire field walked past it. It would take another seventeen years before anyone understood what those repeating sequences were actually for.

Section 3 — Francisco Mojica and the Salt Marshes of Alicante

For the next decade, scattered researchers in different countries independently noticed similar repeated sequences in other bacteria and archaea (single-celled organisms related to bacteria). Each time, the finding was noted, not understood, and set aside. These sequences were given various names: “short regularly spaced repeats,” “tandem repeats,” “repetitive extragenic palindromic sequences.” None of the names stuck. None of the researchers knew they were all looking at the same phenomenon.

Enter Francisco Mojica, a microbiologist at the University of Alicante in Spain. In 1993, as a PhD student, Mojica was studying archaea from the salt marshes near Alicante — extremophile organisms that thrive in the hypersaline water of the salterns (salt-evaporation ponds) along the Spanish Mediterranean coast. The organism was Haloferax mediterranei.

Sequencing its genome, Mojica found the same strange repeating structures that Ishino had noticed in E. coli six years earlier. But unlike Ishino, Mojica became obsessed with them. For the next decade, he spent his career trying to understand what these sequences were and what they did. It was not a glamorous pursuit. His colleagues thought he was wasting his time on genetic junk.

By the early 2000s, Mojica had accumulated enough genomic sequence data from enough different organisms to start seeing a pattern. He found these repeat structures not just in Haloferax but in dozens of different bacteria and archaea — organisms that shared almost nothing else in common. Whatever these sequences were doing, they were doing it across enormous evolutionary distances. That meant they were doing something very important.

In 2003, the moment of insight came. Mojica was analysing the spacer sequences — the unique sequences between the repeats — when he decided to run them through GenBank, the international database of all known DNA sequences. And there it was: the spacers matched sequences in bacteriophage genomes. Not all of them, but enough to make the pattern clear. The bacteria were storing pieces of viral DNA in their own genomes. And crucially, when Mojica looked at which bacteria had which spacers, the matches were to phages known to infect that specific bacterial strain — not to random phages.

The conclusion was breathtaking: these bacteria had been infected by these viruses in the past, had somehow captured a snippet of viral DNA, and had stored it in their genome. This was adaptive immunity — a form of immunological memory — in organisms so simple they don’t even have cells in the conventional sense. Nothing like this had ever been seen in bacteria before. Bacterial immunity was supposed to be crude and non-specific. What Mojica had found was the opposite.

Section 4 — The Paper Nobody Would Publish

Mojica wrote up his findings and submitted them to Nature in 2003. Nature rejected the paper without review. He resubmitted to Nature Molecular Biology. Rejected again. Then Molecular Microbiology. Rejected. Then Nucleic Acids Research. Rejected. The paper bounced around top journals for almost two years, collecting rejection letters that all said roughly the same thing: interesting observation, insufficient mechanistic data, speculative conclusions.

This is one of the most painful episodes in the CRISPR story. The editorial reviewers were not incompetent — Mojica’s paper was indeed speculative, because the mechanism was entirely unknown. He had identified a correlation: bacteria store viral DNA snippets, and those snippets match phages that infect them. But he had no idea how the bacteria used this information to fight infection, or what molecular machinery was involved. Proving a biological memory system from sequence data alone, without a mechanistic story, was simply not how science was supposed to work.

The paper was eventually published in early 2005 in the Journal of Molecular Evolution — a solid but not high-profile journal. By then, three other groups had independently reached the same conclusion about the adaptive immunity function of CRISPR and had beaten Mojica’s paper into print. The phenomenon now had a proper name: CRISPR, coined by Ruud Jansen at Utrecht University in 2002, standing for Clustered Regularly Interspaced Short Palindromic Repeats.

Section 5 — The Yogurt Connection: Industry Accidentally Proves It

One of the stranger twists in the CRISPR story is that its immune function was definitively proven not in a university laboratory but in the industrial microbiology division of a yogurt company. In 2007, scientists at Danisco (now part of DuPont), a Danish food ingredients company, published a paper in Science that provided the first clear experimental proof that CRISPR is a bacterial immune system.

Danisco had a practical problem: the bacteria they use to make yogurt — Streptococcus thermophilus — are constantly attacked by bacteriophages in industrial fermentation tanks. A phage outbreak can destroy an entire batch of yogurt in hours. The company had been systematically selecting for phage-resistant bacterial strains for years, without understanding the mechanism.

Rodolphe Barrangou and Philippe Horvath at Danisco noticed something in their phage-resistant strains: they had acquired new spacers in their CRISPR arrays — spacers that matched the genomes of the phages they had been exposed to. When those spacers were deleted, the bacteria lost their resistance. When the spacers were reintroduced, resistance was restored. This was unambiguous, direct experimental proof: CRISPR spacers carry the immunological memory, and that memory confers specific resistance to the matching phage.

The Danisco paper landed like a thunderclap. Suddenly every microbiologist with an interest in bacterial genetics was paying attention to CRISPR. The field accelerated sharply. Within two years, the Cas proteins associated with CRISPR arrays had been characterised, and researchers were beginning to understand the molecular machinery that turns the spacer information into a defensive response.

Section 6 — Doudna & Charpentier: The Collaboration That Changed Everything

By 2011, the field was moving fast. The CRISPR immune system was understood in outline, but the precise molecular mechanism of interference — exactly how Cas9 found and cut viral DNA — was still unclear. Into this accelerating field stepped two scientists whose collaboration would produce the most consequential biology paper of the 21st century.

Jennifer Doudna at the University of California, Berkeley, was one of the world’s leading RNA biochemists. She had spent her career working on the structural biology of RNA molecules — understanding their three-dimensional shapes and how those shapes enable their functions. CRISPR was an RNA-guided system, so it was natural territory.

Emmanuelle Charpentier, then at the University of Umeå in Sweden, had been studying the CRISPR system in Streptococcus pyogenes (the bacterium that causes strep throat). Her group had made a critical discovery: the Cas9 protein in this organism required not one but two RNA molecules to function. The first was the crRNA (containing the spacer sequence). The second was a previously uncharacterised RNA called the tracrRNA (trans-activating CRISPR RNA). Without the tracrRNA, Cas9 could not cut anything.

Charpentier and Doudna met at a scientific conference in Puerto Rico in 2011. Charpentier was looking for a collaborator with deep expertise in RNA biochemistry to help characterise the tracrRNA and its role in Cas9’s mechanism. Doudna was looking for an interesting new RNA biology problem. The conversation was immediate and productive.

Their collaboration moved quickly. Within months, they had established the key features of the Cas9 mechanism: that Cas9 needed both the crRNA (target-finding) and tracrRNA (Cas9-activating) to cut DNA; that the two RNA molecules could be fused into a single guide RNA without losing function; and most importantly, that if you changed the 20-nucleotide spacer sequence of the guide RNA, you could direct Cas9 to cut a completely different DNA sequence.

That last finding was the breakthrough. It meant that CRISPR-Cas9 was not a fixed-target tool, like earlier gene editing technologies. It was a programmable tool. You could tell it where to cut by changing a short RNA sequence — something that could be synthesised cheaply and quickly in any molecular biology laboratory in the world. The targeting was no longer determined by expensive, time-consuming protein engineering. It was determined by base-pairing chemistry.

Section 7 — The 2012 Paper: A Tool for All of Biology

On June 28, 2012, Doudna, Charpentier, and their colleagues published “A Programmable Dual-RNA-Guided DNA Endonuclease in Adaptive Bacterial Immunity” in Science. The paper demonstrated, in a test tube, that Cas9 guided by a synthetic single guide RNA could cut any target DNA sequence — and that changing the guide RNA sequence redirected the cutting to a new target. The authors explicitly noted the potential for “genome editing and gene expression control” in their discussion.

Scientists who read the paper immediately understood what they were looking at. Here was a system that was:

The citation count of the 2012 paper climbed at a rate unprecedented in the life sciences. By 2015 it had been cited more than 3,000 times. By 2020, more than 15,000. The field of CRISPR biology grew from a handful of dedicated researchers in 2012 to thousands of laboratories worldwide by 2015. The number of published CRISPR papers doubled every year for most of the decade.

Section 8 — The Race to Human Cells & the Patent War

The 2012 Doudna-Charpentier paper showed CRISPR worked in purified biochemical conditions — in a test tube with isolated proteins and DNA. The critical next step was showing it worked inside actual human cells, with all the complexity of a living nucleus: chromatin structure, competing proteins, the epigenome, the machinery of gene regulation.

Several groups were racing to demonstrate this. In January 2013, two papers appeared nearly simultaneously in Science: one from Feng Zhang’s group at the Broad Institute (MIT/Harvard), the other from George Church’s group at Harvard Medical School. Both demonstrated efficient CRISPR-Cas9 editing in human and mouse cells. Feng Zhang’s paper appeared online five days earlier. This timing would become enormously significant.

What followed was one of the most acrimonious patent disputes in the history of biotechnology. Doudna and Charpentier had filed for patents based on their 2012 biochemical work. Zhang had filed patents based on his 2013 work in human cells. Both sets of patents claimed broad rights over CRISPR-Cas9 gene editing. Billions of dollars in potential licensing revenue hung in the balance.

The US Patent Trial and Appeal Board ruled in 2017 that Zhang’s patents (assigned to the Broad Institute) were distinct from Doudna and Charpentier’s patents, and awarded the Broad Institute rights to CRISPR in human and other eukaryotic cells. The dispute continued through appeals for years, and the legal landscape of CRISPR licensing remains complex, with different patent holders controlling different aspects of the technology in different jurisdictions. The science, however, proceeded entirely unimpeded.

Section 9 — The Nobel Prize in Chemistry 2020

On 7 October 2020, the Royal Swedish Academy of Sciences announced that the Nobel Prize in Chemistry would be awarded to Jennifer Doudna and Emmanuelle Charpentier “for the development of a method for genome editing.” It was the first Nobel Prize in Chemistry ever awarded to two women, and only the seventh time in Nobel history that an all-female team had won a scientific prize.

The award was notable for several reasons beyond the gender milestone. It came with remarkable speed — only eight years after the 2012 paper. Nobel Prizes are typically awarded decades after the work, once the field has had time to assess the significance. The speed of the CRISPR Nobel reflected the committee’s judgment that this was simply too important to wait: an FDA-approved therapeutic was already in late-stage clinical trials at the time of the award.

The award also came with controversy. Many scientists felt that Francisco Mojica — who had spent a decade trying to convince the world that CRISPR was an immune system — deserved recognition. Others pointed to Rodolphe Barrangou and Philippe Horvath at Danisco, whose 2007 experimental proof was pivotal. Feng Zhang, who first demonstrated CRISPR editing in human cells, was also widely cited as a potential laureate. The Nobel committee can award the prize to at most three individuals, and in choosing Doudna and Charpentier alone, they focused recognition on the programmable tool rather than the immune system discovery.

Charpentier, reached by phone by a journalist before the official announcement, was characteristically precise: “I hope it will send a positive message to young women who want to follow the path of science and show them that women in science can also have an impact through the research they are performing.”

Section 10 — What Came Next: From Lab Bench to Human Lives

The decade after the 2012 paper was one of the most productive in the history of biology. CRISPR transformed every corner of the life sciences — not just as a therapeutic tool but as a research instrument of extraordinary power.

In research, CRISPR genome-wide screens allowed scientists to systematically knock out every gene in the human genome and observe the consequences — something that would have been impossible before. This approach identified new cancer vulnerabilities, virus entry mechanisms (including the ACE2 receptor that SARS-CoV-2 uses), and disease-relevant genes at a scale and speed previously unimaginable. It transformed basic biological research.

In agriculture, CRISPR accelerated crop improvement programmes. Disease-resistant wheat, drought-tolerant crops, hornless cattle (eliminating a painful management procedure), and salmon with improved feed efficiency were all developed. Regulatory bodies grappled with whether CRISPR-edited crops required the same oversight as traditional GMOs — a question still being resolved differently in different countries.

In medicine, the clinical development pipeline expanded rapidly. By 2020 there were dozens of CRISPR-based clinical trials registered worldwide, targeting diseases from sickle cell and beta-thalassaemia to various cancers, HIV, and rare inherited conditions. In December 2023, the FDA approved Casgevy — the first CRISPR medicine — for sickle cell disease, completing the journey from bacterial salt marsh curiosity to approved human therapy in approximately thirty years.

References & Further Reading