How some bacteria are cleaning up our messy water supply

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The diabetes medication metformin has been touted as a miracle drug. Not only does it keep diabetes in check, but it can reduce inflammation, curb cancer, stave off the worst effects of covid, and perhaps even slow the aging process. No wonder it’s so popular. In the US, the number of metformin prescriptions has more than doubled in less than two decades, from 40 million in 2004 to 91 million in 2021.

Worldwide, we consume more than 100 million kilograms of metformin a year.  That’s staggering.

All that metformin enters the body. But it also exits largely unchanged and ends up in our wastewater. The quantities found there are tiny—tens of micrograms per liter—and not likely to harm humans. But even small amounts can affect aquatic organisms that are literally swimming in it. 

Lawrence Wackett, a biochemist at the University of Minnesota, got interested in this issue about a decade ago. Researchers had observed that at some wastewater treatment plants, the amount of metformin entering was much larger than the amount leaving. In 2022, Wackett’s team and two other groups identified the bacteria responsible for metabolizing the drug and sequenced their genomes. But Wackett still wondered which genes were responsible.

Now he knows. This week, he and his colleagues reported that they have identified two genes encoding proteins that can break down metformin. The study was published in the Proceedings of the National Academy of Sciences. These proteins are produced by at least five species of bacteria found in wastewater sludge across three continents. But here’s what struck me: This isn’t a coincidence. These bacteria evolved the ability to metabolize metformin. They saw an opportunity to capitalize on the ubiquity of the drug in their environment, and they seized it. “This happens all the time,” Wackett says. “Microbes adapt to the chemicals that we make.”

Here’s another example. In the 1960s, farmers began using a new weed killer called atrazine. For about a decade, scientists reported that the chemical appeared to degrade slowly in soil. But about a decade later, that changed. “Everybody was reporting, ‘No, it’s going away really fast—in weeks or a month.” That’s because bacteria evolved the capacity to metabolize atrazine to extract nitrogen. “There is selective pressure,” Wackett says. “The bacteria that figured out how to get that nitrogen out have a big selective advantage.”

This kind of bacterial evolution shouldn’t come as a surprise. We’ve all heard about how the rampant use of antibiotics in people and livestock is driving an antimicrobial resistance crisis. But for some reason, it never occurred to me that bacteria might be evolving in a way that could help us rather than harm us.

That’s good news. Because we have made a real mess of our water supply.

Let’s take a step back. This problem isn’t new. Scientists first detected pharmaceuticals in water more than 40 years ago. But concern has increased dramatically in the past 20 years. In 2008, the Associated Press reported that drinking water in the US was tainted with a wide variety of medications—everything from antibiotics to antidepressants to sex hormones.

It’s not just medicines. A dizzying number of personal care products also end up in the sewers—coconut shampoos and hydrating body washes and expensive face serums and … well, the list goes on and on. Wastewater treatment facilities were never designed to deal with these so-called micropollutants. “For the first 100 years or so of wastewater treatment, you know, the big thing was to prevent infectious diseases,” Wackett says.

Today, many wastewater treatment plants mix wastewater and air in a tank to form an activated sludge—a process that helps bacteria break down pollutants. This system was originally designed to remove nitrogen, phosphates, and organic matter—not pharmaceuticals. When bacteria in the sludge do metabolize drugs like metformin, it’s a happy accident, not the result of intentional design.

Certain technologies that rely on bacteria can do a better job of getting rid of these tiny pollutants. For example, membrane biological reactors combine activated sludge with microfiltration, while biofilm reactors rely on bacteria grown on the surface of membranes. There are even anaerobic “sludge blankets” (worst name ever), in which microbes convert contaminants to biogas in an oxygen-poor environment. But these technologies are expensive, and treatment facilities aren’t required to ensure that treated water is free of these contaminants. At least not in the US.

The European Commission is on its way to adopting new rules stipulating that by 2045, larger wastewater treatment facilities will have to remove a whole host of micropollutants. And in this case, the polluters—pharmaceutical and cosmetics companies—will pay 80% of the cost. The pharmaceutical industry is not a fan of this idea. Trade groups say the new rules will likely result in drug shortages.  

In the US, the federal government is still trying to figure out how to deal with these pollutants. It’s tricky, because it’s not entirely clear what impact small quantities of pharmaceuticals in water will have on the environment and human health. And the risk varies depending on the medication in question. Some pose a clear threat. Oral contraceptives, for example, have caused fertility issues and sex switching in fish. 

Could bacteria save us from estrogen too? Maybe. More than 100 estrogen-degrading microbes have been identified. We just need to find a way to harness them.


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Read more from MIT Technology Review’s archive

In a 2023 issue of The Checkup, my colleague Jessica Hamzelou introduced us to the scientists who study the exposome—all the chemicals we eat, drink, inhale, and digest. Here’s the story.

Hamzelou also wrote about another pervasive pollutant: microplastics. They’re everywhere, and we still don’t really understand what they’re doing to us.  

Microbes aren’t just for cleaning up wastewater. They can also help break down food. And some companies hope to build anaerobic digesters to help them do just that, reported Casey Crownhart last year.

Saima Sidik dove into the fascinating history of how MIT’s innovations in wastewater treatment helped stop the spread of infectious diseases. 

From around the web

Long read: Jane Burns has devoted her life to solving the mystery of Kawasaki disease, a lethal childhood illness that comes on without warning. Now Burns and her oddball team of collaborators have the tools they need to pinpoint the cause.  (NYT)

Older adults should get another covid booster this spring, according to new CDC recommendations. (Washington Post)

Public health officials are “flummoxed” about the Florida surgeon general’s lackluster response to a measles outbreak in the state. (NPR)

After decades of little innovation, biotech finally has a bevy of new drug candidates to treat psychiatric illnesses. “This is a renaissance in neuroscience.” (Stat)

The weird way Alabama’s embryo ruling takes on artificial wombs

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

A ruling by the Alabama Supreme Court last week that frozen embryos stored in labs count as children is sending “shock waves” through the fertility industry and stoking fears that in vitro fertilization is getting swept up into the abortion debate.

The New York Times reports that one clinic, at the University of Alabama, has stopped fertilizing eggs in its laboratory, fearing potential criminal prosecution.

Fertility centers create millions of embryos a year. Some are frozen and others used in research, but most are intended to be transplanted into patients’ wombs so they can get pregnant. 

The Alabama legal ruling is clearly animated by religion—there are lots of Bible quotes and references to “murder” when discussing abortion. But what hasn’t gotten as much notice is the court’s specific argument that an embryo is a child “regardless of its location.” This could have implications for future technologies in development, such as artificial wombs or synthetic embryos made from stem cells. 

The case arose from an incident at an Alabama IVF clinic, the Center for Reproductive Medicine, in which a patient wandered into a storage area and removed a container of embryos from liquid nitrogen. 

That’s when “the subzero temperatures at which the embryos had been stored freeze-burned the patient’s hand, causing the patient to drop the embryos on the floor,” the decision recounts. The embryos, consisting of just a few cells, thawed out and died.

Angered by the mishap, some families then tried to collect financial damages. They sued under Alabama’s Wrongful Death of a Minor statute, which was first written in 1872, long before test-tube babies.

The question the court felt it had to decide: Do frozen embryos count as minor children or not? 

The defendants argued, in part, that an IVF embryo can’t be a child or a person because it’s not yet in a biological womb. No womb, no baby, no birth, and no child. And this is where things start to get interesting and spiral into science fiction territory. 

Justice Jay Mitchell, writing for the majority, pounced on what he called the “latent implication” of the defense’s argument. What about a baby growing to term an artificial womb? Would it also not count as a person, he asked, just because it’s not “in utero”?

According to their ruling, the wrongful-death act “applies to all unborn children, regardless of their location,” and “no exception” can be made for embryos regardless of their age, even if they’ve been in deep freeze for a decade. Nor does the law exclude any type of “extrauterine children” science can conceive.

It’s common for judges to wrestle with complex questions as they try to apply old laws to new technology. But what’s so unusual about this decision is that the judges ended up ruling on technology that hasn’t been fully invented.

“I think the opinion is really extraordinary,” says Susan Wolf, a professor of law and medicine at the University of Minnesota. “I can’t think of another case where a court powered its ruling by looking not only at technology not actually before the court, but number two, that doesn’t exist in human beings. They can’t make a binding decision about future technology that is not even part of the case.” 

Bad law or not, the question the Alabama justices ruled on could soon be a real one. Several companies are actually developing artificial wombs to keep very premature infants alive, and other research labs are working with fluid-filled bottles in which they’ve grown mouse embryos until they are fetuses with beating hearts. 

One startup company in Israel, Renewal Bio, says it wants to grow synthetic human embryos (the kind formed by stem cells) until they are 40 days old, or more, in order to collect their tissue for transplant medicine. 

All this technology is racing along, so the question of the moral and legal rights of incubated human fetuses might not be hypothetical for very long. 

Among the dilemmas lawyers and doctors could face: If a fetus is growing in a tank, would a decision to shut off its support systems be protected under liberal states’ abortion laws, which are typically based on the rights of a pregnant person? Would a fetus engineered solely to grow organs, lacking a brain cortex and without sentience, also still be considered a child in Alabama?

So while it’s obvious that the Alabama decision reflects the justices’ religious views rather than science, and that it could hurt people who just want to have a baby, maybe it is time to think about what the court calls the “many difficult questions” the wrongful-death case has raised about “the ethical status of extrauterine children.”


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For the first time, you can easily order GMOs to plant at home. The biotech plants on sale include a bright-purple tomato and a petunia plant that glows in the dark. (MIT Technology Review)

From MIT Technology Review’s archives

Last fall, my colleague Cassandra Willyard told us everything we need to know about artificial wombs. The experimental devices, she explained, are being developed to give premature babies more time to develop. So far, they’ve been tested on lambs, but human studies are being planned.

Another kind of artificial womb is used to keep very early embryos developing longer in the lab. A startup based in Israel called Renewal Bio says it hopes to grow “synthetic” human embryos this way longer than ever before as a way of bio-printing organs. 

After the US Supreme Court overturned abortion protections in 2022, several American states moved to ban the practice. Anticipating that people may seek abortions anyway, we explained how to end a pregnancy with pills ordered from an online pharmacy. 

Around the web

Elon Musk announced on X that the first volunteer to receive a brain implant from his company Neuralink can control a computer with it and can “move a mouse around the screen just by thinking.” Some commentators are annoyed at Musk for grabbing publicity while revealing few details about the study. (Wired

China is the country with the world’s largest population. It has the most obese people—about 200 million of them. But new weight-loss drugs are in short supply there. (WSJ)

Ready, set, grow: These are the biotech plants you can buy now

This spring I am looking forward to growing some biotech in my backyard for the first time. It’s possible because of startups that have started selling genetically engineered plants directly to consumers, including a bright-purple tomato and a petunia that glows in the dark.

This week, for $73, I ordered both by pressing a few buttons online.

Biotech seeds have been a huge business for a while. In fact, by sheer mass, GMOs are probably the single most significant product of genetic engineering ever. Except most of us aren’t planting rows of cotton or corn that can resist worms or survive a spritz of RoundUp, the big gene-splicing innovations that companies like Monsanto and Pioneer Hi-Bred first introduced in the 1990s.

What makes these new plants different is that you can buy them directly from their creators and then plant them in the yard, on a balcony, or just in a pot. 

caprese salad in a bowl made with halved yellow, red and purple-fleshed cherry tomatoes
Purple tomatoes developed by Norfolk Health Produce.
NORFOLK HEALTHY PRODUCE

Purple tomato

Starting off my biotech shopping spree, I first spent $20 to order 10 tomato seeds from Norfolk Health Produce, a small company in Davis, California, that created what it calls the Purple Tomato. The seeds have a gene introduced from a snapdragon flower, which adds a nutrient, anthocyanin, that also gives the fruits their striking color.

According to Channa S. Prakash, a geneticist and dean at Tuskegee University, the tomato is the “the first-of-its kind GMO food crop marketed directly to home gardeners.”   

The CEO of the company, Nathan Pumplin, was packing seeds when I reached him by phone. He claimed that anthocyanin has health benefits—it’s an antioxidant—but he agreed that the color is a useful sales pitch.

“I don’t need to make a label that says this red tomato is better for you than the other red tomato,” says Pumplin. “We can simply put out the purple tomato, and people say, ‘Oh my gosh, this tomato is purple.’ Its beauty is a distinguishing characteristic that people can just immediately see and understand.”

There is a plan to mass-produce the purple tomatoes for sale in supermarkets. But Pumplin says the company couldn’t ignore thousands of requests from regular gardeners. “It’s not the main focus of our business, but we are very interested in having people grow these at home,” he says. And “if home gardeners want to save the seed and replant it in their gardens for their own use, that is okay.”

couple in their glowing garden of gmo petunias
A promotional video for Light Bio’s firefly petunia.
LIGHT BIO

Glowing flower

I next decided to shell out for the “firefly petunia,” so called because the plant is supposed to glow in the dark. It’s sold by Light Bio, a startup backed by the venture capital firm NFX .

The plant is such a novelty that it’s being sold in a preorder, with promises they will arrive by May. One petunia plant costs $29 plus $24 for shipping. The company’s marketing promises that your plant will unveil “mesmerizing luminescence after dusk” and that “its soothing light is produced from living energy, cultivating a deeper connection with the inner life of the plant.” 

Finally, “Your nurturing care will be rewarded with even greater brilliance.”

It joins a short list of ornamental plants with gene modifications. Another is an orange petunia, approved in the US in 2021, that got its unusual color from a corn gene. (When some copies got loose prior to approval, officials in the US and Europe demanded its eradication in what became known as “the petunia carnage.”) 

Karen Sarkisyan, a synthetic biologist at the MRC Laboratory of Medical Sciences in the UK, is one of the petunia’s creators, and also the chief scientist of Light Bio. His lab is interested in using bioluminescence as a reporter system—a plant could reveal, for instance, how it responds to a toxin or viral infection in lab experiments. 

“In general, we’re trying to make useful things, so this is more of an exception,” he says of the firefly petunia. “The motivation was more about merging biology and art, rather than utility.”

Like a lot of things in biotech, making a glowing petunia was not easy to do—it’s the seemingly sudden result of decades of research into the chemistry that permits certain plants and animals to glow faintly.

Imposing those genetic circuits on plants did not work too well at first. Several years ago, for instance, a Kickstarter project that raised nearly $500,000 to make glowing roses failed to deliver on its promises after the project proved too difficult.

 “It was fairly obvious … that there was no good technology at that time,” says Sarkisyan, who later played a role in discovering genes from a glowing fungus which, after being added to a petunia, made it shine brightly enough to work as a novelty item.

That work continues. Sarkisyan says the company is working on “increasing the brightness and making more colors.” It’s also working on making other types of plants glow, although which ones remain a secret. “I cannot really comment on specific species we’re working on,” he says, although he did show me a photo of a spectacular glowing chrysanthemum.

side view of a genetically modified glowing plant at night
Plants made by Light Bio.
LIGHT BIO

Sarkisyan told me he sometimes likes to relax among the glowing plants and have a meditative experience. Ironically, he can only do that in the lab and not at home, since he lives in the UK. The country, which takes a stricter view on GMOs, has not approved the plants for sale (neither has Europe).

But he thinks the petunia could win over critics. “Especially with all the talk and concerns about the GM stuff, this is the first time there can be a safe, friendly, pleasant GM house plant in every home,” he says. “We think it’s a very interesting project because it is one of the first in consumer biotech. I do think we will see more and more in the future.”

My tomato seeds and glowing petunia haven’t arrived in the mail yet, and there’s still snow where I am. But come spring, I hope to be putting my first biotech crop in the ground. 

How bacteria-fighting viruses could go mainstream

This article first appeared in The Checkup, MIT Technology Review’s weekly biotech newsletter. To receive it in your inbox every Thursday, and read articles like this first, sign up here.

Lynn Cole had a blood infection she couldn’t shake. For years, she was in and out of the hospital. Each time antibiotics would force the infection to retreat. Each time it came roaring back.

In the summer of 2020, the bacteria flooding Cole’s bloodstream stopped responding to antibiotics. She was running out of time. Her doctors decided they had to try a different approach, and asked the US Food and Drug Administration  to allow them to administer an experimental therapy, a virus known as a bacteriophage. Bacteriophages — or phages — are tiny viruses that infect and destroy bacteria.

What happened next? The details came out this week in a case study in mBio. The phages worked. Cole recovered with remarkable speed. But then the therapy failed. Cole’s case highlights the enormous promise of phage therapy, but it also shows just how much we have to learn.

Welcome back to the Checkup. Let’s talk phages. (Or rather, let’s talk about phages again.) What will it finally take to bring phage therapy into mainstream medicine?

Phage therapy has been around for more than a century, but it fell out of fashion throughout most of the world with the advent of antibiotics. The deepening antimicrobial crisis, however, has rekindled people’s interest and generated an enormous amount of excitement. Headlines have claimed that phages can “save the world” and that “one day, doctors might prescribe viruses instead of antibiotics.”

The excitement reached a fever pitch in recent years because of one particularly compelling story. In 2016, HIV researcher Tom Patterson picked up a deadly antibiotic-resistant infection in Egypt. His wife, infectious disease epidemiologist Steffanie Strathdee, helped hunt for the phage therapy that ultimately cured him. Strathdee gave a TED talk. She and Patterson wrote a book. She told her story in People magazine.

Stories like this have cast phages as a miracle cure. And these tiny viruses do have a lot of things going for them. They target bacteria with stunning specificity. “We think of phage as a targeted missile,” says Daria Van Tyne, an infectious disease researcher at the University of Pittsburgh and co-author of  the new case study. This missile can “take out a specific species or strain that is causing the infection, but to leave other commensal bacteria unharmed.” What’s more, phages aren’t as likely to drive bacterial resistance as antibiotics. And they’re wildly abundant. “You can go to a drop of seawater and find trillions of phages,” Van Tyne adds.  

But for many people, phages aren’t some miraculous elixir.  In 2022, researchers published the largest series of case studies of phage therapy for antibiotic-resistant bacterial infections yet. Of the 20 people treated with phages, most with infections related to cystic fibrosis, 11 had a positive response to the therapy. However, only five managed to totally clear their infections. Another six had some partial response. The rest failed to respond or their results were inconclusive. 

Let’s go back to Lynn Cole.

When Cole first received phage therapy, she had been dealing with a blood infection for nearly a month. Her doctors tried a variety of antibiotics with no effect. But 24 hours after they administered phage therapy, Cole’s infection was gone. She seemed cured.

About a month later, however, the infection returned. So the researchers found another phage that would work against the Enterococcus bacteria causing Cole’s infection, and began administering both phages. That seemed to do the trick.

For four months, Cole was infection-free. She left the hospital and went on vacation with her family. But then the infection returned. Cole was out of options. She entered hospice, and seven months later she died of pneumonia.

Van Tyne and her colleagues have spent the past couple of years trying to explain why their phages failed. They don’t yet have an answer, but they do have a hypothesis. A couple of weeks after Cole began receiving the second phage, she developed antibodies against both phages. “Possibly that played a role in limiting how well they were able to find their bacterial targets and kill them,” says Madison Stellfox, a physician and postdoc in Van Tyne’s lab. She posits that perhaps the antibodies coated the phages so they couldn’t enter the bacteria. Or maybe they helped the body clear the phages faster, so they didn’t have time to work.

Cole isn’t the only patient Van Tyne and her colleagues at the University of Pittsburgh have treated. Since Van Tyne started her own lab in 2018, she has developed a library that contains about 200 phages, most isolated from Pittsburgh’s wastewater. Those phages target six or seven species of bacteria. They use that library to develop personalized therapies for patients with life-threatening infections. “We’re trying to match clinical isolates from infected patients with phages that are active on them,” Van Tyne says. 

The team has treated nearly 20 patients. Some have cleared their infections. Some, like Cole, have experienced temporary improvements. Some have had no response at all. But reassuringly, no one has been harmed by the therapy itself.  

All these patients were treated under the FDA’s “compassionate use” program, which provides access to investigational therapies for people with life-threatening illnesses. Case studies can provide valuable insights, but they’re not a pathway to regulatory approval. To move phages into mainstream medicine, we need clinical trials.

Alexander Sulakvelidze, president and chief executive officer at the phage company Intralytix, has been working to develop phage products since the 1990s. In the Republic of Georgia, where he was born, phage therapy is routinely used to treat infections.  

But in the US phage therapy was a hard sell. Intralytix, which launched in 1998, started with baby steps, first seeking approval for phage products to fight bacterial contamination in food products. Now, however, the company is generating revenues, and it has three clinical trials underway to test phage cocktails against three antibiotic-resistant bacteria. But these are trials to assess safety, not the large pivotal trials needed for FDA approval. “That’s why I’m saying it will be several years until [these therapies] see the light of  day,” Sulakvelidze says.

The Los Angeles-based company Armata Pharmaceuticals, led by Deborah Birx (yes, that Deborah Birx), is also testing its phage therapies in trials. The company plans to launch an efficacy study, which could be used to seek regulatory approval, in the coming year, although it has yet to find a partner to help fund that endeavor. This kind of pivotal trial will help get pharma interested in phage therapy, and “that’s the only way it’s going to get completely commercialized,” Birx says. A pivotal trial will also provide some solid data on whether phages are effective. “It is worth moving forward to get a definitive answer,” she adds. “Because otherwise we’re just going to wait, and we’ll be sitting here 20 years from now saying ‘are phages important or not?’”

Read more from MIT Technology Review’s archive

Dig way back in our archives, and you’ll find a piece from 2001 about how phages could be turned into a new class of antibiotics. Paroma Basu has the story

Last year, in a previous issue of the Checkup, Jessica Hamzelou  wrote about the comeback of phage therapy

A phage cocktail saved a teen with cystic fibrosis from an antibiotic-resistant infection. Charlotte Jee gave us the details in 2019.

DNA sequencing and AI could make it easier for doctors to match infections with the right phage cocktail, Emily Mullin wrote in 2018

From around the web

The CDC plans to ditch its Covid five-day isolation policy in favor of a policy that is based on symptoms. The new policy would allow people to stop isolating once their symptoms are mild and they’ve been fever-free for at least 24 hours without medication. (Washington Post)

Dengue is surging in Brazil, prompting Rio de Janeiro to declare a public health emergency. (NYT)

Deep dive: Environmental DNA could help provide an early warning of the next pandemic. (Undark)

A journal retracted three abortion studies that suggested that medication abortion is dangerous after it found that the conclusions were based on faulty assumptions and a misleading presentation of the data. (NYT)

Uruguay wants to use gene drives to eradicate devastating screwworms

On a warm, sunny day in Montevideo, Uruguay, the air is smogless and crisp. Inside a highly secured facility at the National Institute of Agricultural Research (INIA) are a sophisticated gene gun, giant microscopes, and tens of thousands of gene-edited flies, their bright blue wings fluttering against the walls of their small, white, netted cages.

These flies—shown to me on video by an INIA veterinarian, Alejo Menchaca—are a new weapon that may soon be unleashed against an enemy that kills cattle and costs the livestock industry millions of dollars every year: the New World screwworm, a parasite common in parts of South America and the Caribbean. 

When a female screwworm fly attacks cattle, it lays eggs, which hatch and turn into worm-like larvae that screw down into the host animal, feeding on flesh along their way and damaging the animal’s skin. Left untreated, the animals eventually die in excruciating agony. 

But Menchaca and colleagues have a plan. Using the genome-editing system CRISPR, they’ve developed what’s known as a gene drive, a type of genetic element that manipulates the reproductive process to spread farther and faster than an ordinary gene. They are about to move into the next stage of caged trials in the lab, with a view to eventually using the genetic tool to decimate the screwworm fly population. They have received a $450,000 grant from the Inter-American Development Bank (IDB) for the research.

“With gene drives, we can control these pests in precise and effective ways,” says Menchaca.

The scientific team in Uruguay poses in a lab.

COURTESY OF ALEJO MENCHACA

Gene drives occur naturally in the wild, but the technology for making them deliberately is new and still pretty controversial. CRISPR allows scientists to cut specific genes in any organism’s DNA and replace them with new sequences. It can be used to tweak an animal’s DNA in a way that affects the species’ survival, often by making the females sterile, when it spreads in the population through breeding. 

Some organizations have been trying to develop gene drives to eradicate mosquitoes. Target Malaria, supported by the Seattle-based Bill & Melinda Gates Foundation (BMGF), is currently the most advanced gene-drive project in the world. But even then, they have never gone beyond caged trials. The process of getting permission for field release efforts has crawled.    

In 2020, the INIA researchers received permission from the Uruguayan government to test their techniques through the country’s existing National Program for Control of Screwworms. Right now, they’re experimenting with different components of the gene drive in gene-edited screwworm flies in the lab. The plan is to create a population of male screwworms with edited versions of genes that are essential for fertility in the female screwworms. When the engineered males are released into the wild, they should mate with females and pass on that gene.

Over successive generations, more and more female screwworms will inherit copies of the gene drive and become sterile, causing a population crash. 

“The thing that’s attractive is if you knock a gene drive into the female, you could disrupt female development,” says Maxwell Scott, an entomologist at North Carolina State University who is working with the Uruguayan team. “It’s potentially a very efficient system.”

The situation is urgent. In July of last year, Panama declared a state of animal health emergency amid outbreaks of cattle screwworm throughout the country. And this February, more than 200 cases of screwworm attacks on animals were reported in Costa Rica, prompting the government to declare an emergency as well. In Uruguay, screwworm flies cost the livestock industry $40 million to $154 million a year. Agricultural export is the linchpin of Uruguay’s economy—over 80% of the goods the nation exports are agricultural products. Beef, which accounts for 20% of that, is worth $2.5 billion a year. 

That makes the country’s search for new tools to combat the pests even more critical, says Carmine Paolo De Salvo, a rural development expert at the IDB. “The [Uruguayan] government is under constant pressure to do something about it,” he says.

Scientists have been trying to tackle screwworms for decades. One method, known as the sterile insect technique (SIT), was developed by researchers at the US Department of Agriculture in the 1950s. SIT involves sterilizing male screwworm flies with radiation. Then, using airplanes, the DNA-damaged males are dropped on the area of infestation. When they mate with wild female flies, the eggs that are produced do not hatch, slowing population growth and preventing the spread of the parasite.

That approach has worked in many countries, including parts of Central America, freeing livestock and wildlife by the millions from the painful grip of the pests. In the US, an area-wide eradication program using SIT worked so well that in 1966, the USDA declared screwworm eradicated within the nation’s borders. The benefits to the livestock industry were immense: producers saved up to $900 million, and the health of both wild and farm animals improved. 

Even with sterile males, eradicating screwworms remains a stubborn challenge, however. To prevent the screwworms from returning, the US—along with Central and South American countries—still runs a permanent barrier zone of sterile flies on the Panama-Colombia border, requiring a continuous supply of billions of flies every year. This effort is too expensive, and it’s simply not powerful enough to eradicate screwworm in South America, where the pests are firmly established and difficult to surveil, researchers say. So the search has been on for alternative tools.

Screwworm flies are seen in a laboratory.

COURTESY OF ALEJO MENCHACA

It was Kevin Esvelt, a pioneering leader in CRISPR gene-drive systems, who first turned the team on to the idea of using one. Esvelt had been experimenting with engineering localized versions of gene drives to target Lyme disease in the US when he met the team of Uruguayan researchers on a tour of the MIT Media Lab. Shortly after that meeting, Esvelt was on a plane to Uruguay, where he met Menchaca and convinced Uruguayan officials to initiate a gene drive project to eradicate screwworms. This would have the advantage over SIT because while SIT reduces the number of successful births, the infertility conferred by the gene drive passes through multiple generations.

The team is looking to use an approach that Scott has successfully developed for livestock pests. In a recent study, Scott and his team tested it on the spotted-wing drosophila, an invasive fly that attacks soft-skinned fruit. The gene drive they developed for that study carried an edited version of the so-called doublesex gene, which is essential for the fly’s reproduction. In caged trials, they combined the engineered fly population with a population that didn’t have the gene edits, mimicking a real-world release. They found that the gene drive was copied at a rate of 94% to 99%—beyond the efficiency they had expected. ​“It was the first really efficient-homing gene drive for suppression of an agricultural pest,” says Scott. He hopes that a similar technique will work with screwworms and allow researchers to perform safer tests.

It won’t be a quick process. Assembling the gene-drive system, testing it, and securing approvals for field release could take many years, says Jackson Champer, a researcher at Peking University in Beijing, who is not part of the Uruguayan team. “It’s not an easy task; there have been many failed attempts at gene drives.” 

Menchaca agrees. He says he and his colleagues aim to integrate their system into the flies and validate the technology in two to three years, adding that they hope to seek permission for field testing and will consider inviting companies to participate in scaling up the technology in the future.

However, Esvelt hopes the Uruguayan researchers will one day be able to release and test their altered screwworms in the wild. He believes that Uruguay’s robust regulatory environment makes the country a likely site for such experiments.

“This would be a project run effectively by Uruguayans, for the benefit of Uruguay, and may be offered eventually—if it works well—to a broader array of folks throughout South America,” he says.