The team modified the DNA of fruit flies and zebrafish by inserting variants of genes from bacteria to make two enzymes that together can convert methylmercury to elemental mercury which evaporates from the animals as a gas. Credit: CHRISTOPHE ARCHAMBAULT/AFP via Getty ImagesShareScientists from Australia have successfully bioengineered genetically modified fruit flies and zebrafish capable of absorbing toxic mercury and releasing it back into the environment in a less harmful form. The breakthrough, made possible by exposing the flies and fish to a pair of detoxifying enzymes found in microbes, meant the modified flies and fish were able to ingest mercury and safely convert it at far greater rates than their non-modified cousins. The findings were published this week in the journal Nature Communication.But the findings could also have wider implications beyond flies and fish. Zooming out from the test animals, the experiment proves its possible to degrade environmentally harmful mercury early before it manages to wind its way up food supplies and, eventually, human bodies. These are just the latest examples of researchers using modern science to slightly modify the genes of organisms with the ultimate goal of sending them out into the wild to reduce environmental toxins and combat diseases. Actually deploying these science experiments at a scale that can make a meaningful difference however requires navigating through legal, ethical, and regulatory barriers that are sometimes trickier to solve than the underlying science powering the discoveries.Mercury exposure is dangerous and its getting worseMercury is a natural but toxic element that is released into the Earths atmosphere. Methylmercury, a particularly poisonous form of the element, is of particular concern to humans because it gets biomagnified as it works its way through the oceans food web. Humans who eat fish that have eaten smaller aquatic life with methylmercury in their bodies can potentially be exposed to dangerous levels of methylmercury that acts like a neurotoxin. Once ingested by a human, methylmercury isnt easily excreted and can quickly cross the digestive tract, the blood-brain barrier, and the placenta. And while mercury is naturally occurring, recent research shows industrial activities like gold and coal mining are making mercury pollution much worse.The researchers from Macquarie University and the ARC Centre of Excellence in Synthetic Biology in Australia wanted to see if it would be possible to engineer organisms that could interfere with that bioaccumulation process early on in the food cycles, a concept broadly called bioremediation. They settled on two different test subjects: the common fruit fly (an invertebrate) and a zebrafish (a vertebrate). They then injected the embryos of these creatures with a pair of enzymes, MerB (organomercurial lyase) and MerA (mercuric reductase), found in many microbes. These enzymes were chosen for their natural detoxifying properties. When exposed to methylmercury, the enzymes catalyze the protonolysis of methylmercury and naturally transform it into the less toxic elemental mercury (Hg0). Get the Popular Science newsletter By signing up you agree to our Terms of Service and Privacy Policy.Both modified and non-modified versions of the flies and fish were exposed to mercury. The results were impressive. After three days, the genetically modified fruit fly larvae had 83% less methylmercury present than the control group. Similarly, the engineered zebrafish also showed 64% lower levels of harmful mercury than their non-modified counterparts after six days. In both cases, the modified animals had successfully converted the toxic methylmercury into a far less poisonous elemental mercury or Hg0.When we tested the modified animals, we found that not only did they have less than half as much mercury in their bodies, but the majority of the mercury was in a much less bioavailable form than methylmercury, Macquarie University biologist Kate Tepper said in a statement.It still seems like magic to me that we can use synthetic biology to convert the most environmentally harmful form of mercury and evaporate it out of an animal, Tepper addedReleasing modified animals in the wild can create unintended consequencesThis isnt the first time scientists have tried to use genetically altered animals to reshape their broader environments. For years, researchers have been introducing modified mosquitoes with self-limiting genes to mate with other disease-carrying mosquitoes to cut down their population sizes. Researchers and startups are hopeful new bacteria genetically engineered to munch on plastics could one day cut down on ocean pollution and possibly play a role in reducing microplastics that make their way into human bodies. Recent advances in CRISPR-Cas9, which lets scientists make alterations to DNA sequences with far more precision than previously possible, make once improbable-sounding genetic modification now comfortable within reach.But being technically or scientifically possible isnt the same thing as being possible. Any large-scale efforts to release genetically modified animals into natural environments at scale also run the risk of diverting from their intended goals. Theres a long history of humans introducing non-native species into environments with one stated goal only to have them unintentionally decimate other populations. Those concerns around possible invasive species may get amplified further when the creature being introduced has been gene edited in a lab.The researchers behind mercury munching flies and fish seemed to agree, for now at least. Though they say they took some safety precautions to ensure their organisms could not spread uncontrollable in nature, they noted the research is still early and needs more testing before anyone thinks about wide-scale deployment. Still, the findings show the potential, at least in theory, to use gene editing to help solve currently existing environment dilemmas.