Robyn Williams: Next a revolution in gene editing, one you've heard about, but not perhaps about one of the stars of the science, who has just been a guest of the University of New South Wales. Michael Slezak reports.

Michael Slezak: 25 years ago Professor Francisco Mojica was studying for his PhD at the University of Alicante on the Mediterranean coast of Spain when he stumbled across something that would change the world forever. He was examining a strange type of bacteria, one that thrived in the salt marshes near his university. He wanted to understand what genes allowed them to live in those harsh, dry environments. But what he discovered turned out to be what is now called CRISPR, something that would soon be turned into a powerful gene editing tool, that today is capable of things even science fiction writers never dreamed of.

CRISPER Cas9, as it's called, allows scientists to easily, cheaply and accurately delete or change genes in any living thing, effectively allowing scientists to rewrite the code of life. Its promises include treating cancers, creating immunity to HIV, and curing genetic diseases like Huntington's in embryos.

It has also led to concerns about so-called designer babies, and its ability to be weaponised and to spread new genes throughout a population has led to its discoverers, including Professor Mojica himself, to call for caution and regulation. But when Professor Mojica made what some have called the discovery of the century, he was young and not from one of the world's top institutions. He was an outsider. As a result, he faced an uphill battle convincing the scientific community he had found something at all noteworthy.

Francisco Mojica: We were sequencing one region of the chromosome of this microorganism, and we saw that in the region of this chromosome there were exactly the same short sequence repeated many times, and that was very unexpected.

Michael Slezak: He had no idea what these repeated bits of code were doing, but he was pretty sure they must be important.

Francisco Mojica: Just because the space within a very small cell is quite limited, the DNA is also limited, so any information there must be important. And when you think that this percentage of this genome dedicated to repeat once and once again many times exactly the same sequence, you say, oh, it must be something very significant for the cell.

Michael Slezak: For the next 10 years, Professor Mojica studied these strange repeats. Slowly he found them in more and more bacteria, including very distantly related ones, suggesting they were conserved over billions of years of evolution and so must be important. Then some simple experiments showed they were crucial to the bacteria's survival. When they were removed, the bacteria often died. But he still had no idea what they were doing.

After a decade of work though, he made a crucial discovery. Between the repeat sequences he found there was a bit of genetic code that was incompatible with the bacteria it was in. It was like a foreign bit of DNA, DNA from some other organism had been cut and pasted into the bacteria's own genome. Then he discovered that in each case the foreign DNA belonged to a type of virus that commonly infected that bacteria. Not only that, but when a bacterial cell had that viral DNA in its genome, it turned out to be resistant to infection by that virus.

Francisco Mojica: We understood at that moment that we were dealing with an immune system.

Merlin Crossley: So if you are a bacterium, your biggest fear is a virus will come into you, use your body to replicate, and then burst you to pieces. So you want to stop that happening.

Michael Slezak: Professor Merlin Crossley from the University of New South Wales in Sydney.

Merlin Crossley: So this is a bit like human antibodies. If you've been infected once, you have a snapshot of that and you are ready for next time. And what CRISPR does is takes a little piece of the viral DNA, puts it in the bacteria's genome, so next time that virus comes along the bacteria is ready.

Michael Slezak: So CRISPR turned out to be like a natural cut-and-paste tool for DNA. That key discovery was taken and developed by many other scientists into the powerful gene editing tool it is today. Research figured out how to use it to cut up DNA not just in bacteria but in any living thing, and how to direct it to cut and paste exactly what they wanted it to.

Merlin Crossley: We are the product of our DNA, and if you have a gene for red hair, we could go in cells that make the hair, change the gene for red hair to a gene, say, for blonde hair.

Michael Slezak: And way back in 2003, Professor Mojica had a fair hunch of the importance of his discovery.

Francisco Mojica: Immediately we tried to publish this, and also we said this is going to have a tremendous repercussion in biology, in biotechnology and clinical sciences.

Michael Slezak: But the reception to Professor Mojica's findings was a far cry from the excitement around it today.

Francisco Mojica: They didn't believe us. The paper was not accepted, so we tried once again with another journal, another one, another one, up to four different journals.

Merlin Crossley: When you stumble across a nugget of gold, most people will tell you it's fool's gold and it's hard to tell whether it really is. Here was a researcher working in a small University in Spain, people couldn't appreciate the importance of what he'd found. And it's only now that we appreciate the full importance.

Michael Slezak: Professor Mojica agrees being an outsider, not coming from somewhere like Harvard, meant his ideas weren't readily accepted. But the hostile reception was also due to how surprising the findings were.

Francisco Mojica: This was such an unexpected finding, that reviewers were trying to accept that was real. I met someone a few years ago, a scientist who told me, 'I have to confess, I was one of the referees of your paper and I rejected the paper twice.' And I said, 'Why did you do that?' And he said, 'I couldn't believe it, I just couldn't believe it. And still now I wonder how you were able to understand at that time that we were dealing with an immune system.'

Michael Slezak: To develop Professor Mojica's discovery into the gene editing technology it is today took a lot of other amazing scientists.

Francisco Mojica: Now I cannot believe it. If you think about all the technology that has been developed from this immune system, it was not possible even to imagine this is going to happen because maybe you can get a tool from bacteria to do something very particular, but when you get the best molecular biology tools ever for genome editing, for molecular diagnosis, to store information into living beings, into bacteria from any source, these are many tools, different tools, and the best in every single field. So that's amazing, just coming from one single discovery.

Michael Slezak: Are there some applications of CRISPR that have you most excited when you read about them?

Francisco Mojica: Well, there are many applications, very exciting applications of CRISPR. Feng Zhang from the Broad Institute in the States was able to develop a molecular diagnosis method. They call it Sherlock, and it's able to detect a single molecule of a virus, for instance the Zika virus or the dengue virus, in a sample where you have 1018 other molecules, just a single molecule out of millions and millions of other molecules. You can do that in a few seconds, at a price that is about one Australian dollar, using just a strip of paper that you can carry in your pocket and go to any isolated village to know whether people there are infected by a virus. Wow.

Michael Slezak: But perhaps the biggest thing about CRISPR is how cheap and easy it is to use.

Francisco Mojica: CRISPR has democratised genome editing. I know many research groups, they never thought about the possibility of doing themselves, modifications of their DNA, and they are doing it right now because it's so easy.

Michael Slezak: But that democratisation and CRISPR's power has led Professor Mojica and other leading scientists to urge caution.

Francisco Mojica: I'm really worried and concerned about the use of this so powerful tool to do things that shouldn't be done. Almost anyone can use and can get these tools and use them to modify the genome of any living being. Also you can use this tool to kill probably people directly or indirectly. We really need regulation on that, a global rule.

Michael Slezak: But despite his excitement watching that technology develop, Professor Mojica's continued work on CRISPR is driven by something much more esoteric.

Francisco Mojica: I've been working with CRISPR when no one else cared, so now I'm actually working on CRISPR. There are many other CRISPR systems in nature that could be interesting in terms of knowing how they work. After my studies, modules have developed that will be great but I have to confess that's not my goal, I just want to know.

Robyn Williams: Professor Francisco Mojica was a guest at the University of New South Wales, and that report from Michael Slezak from ABC News.