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MIT Better World

By Ari Daniel

When the principal investigator on a multimillion-dollar grant abruptly pulled out of a project, Voigt had eagerly stepped up, writing an entire section from scratch on how to use synthetic biology to improve photosynthesis. “I was like, this is my big opportunity,” he recalls. Yet, when the grant reviews came back, Voigt’s section tanked. It was a devastating blow. He even told his wife he was quitting.

But then a colleague invited him to a meeting and said, “You just picked the wrong system. If you take these same ideas and apply them to nitrogen fixation, you could have a real impact.”

Those words changed the course of Voigt’s career. He and his then-nascent lab plowed into the challenge of using synthetic biology—advanced genetic engineering—to supply agricultural plants with the nitrogen they need to grow and flourish.

The team published a groundbreaking paper demonstrating the technique in 2012, around the time Voigt was recruited to MIT, where he is now the Daniel I.C. Wang Professor and head of the Department of Biological Engineering. In those early days, MIT, notably the Abdul Latif Jameel Water and Food Systems Lab, provided Voigt with critical startup funds to sustain and amplify his research.

Nitrogen fixation

Here’s the problem Voigt is trying to solve: There is plenty of nitrogen gas in the atmosphere, but in that form, it’s inaccessible to most plants.

Some species partner with bacteria that use special enzymes to convert—or “fix”—nitrogen gas into ammonia, which the plants then use. But Voigt says that corn, rice, and wheat which constitute about half the calories we consume—can’t do that. Without sufficient nitrogen, a plant like corn yellows, wilts, and becomes stunted, producing fewer and smaller ears. The result, in other words, is easily visible; it’s not “something that’s hidden or under the earth,” says Voigt.

To provide crops with the nitrogen they need, farms tend to smother them with artificial fertilizers, dumping millions of tons of ammonia onto the soil every year. Making these fertilizers requires enormous amounts of energy and creates about 2.5% of global greenhouse gas emissions.

The lab of Christopher Voigt uses biological engineering to build a future of climate-resilient crops grown with lower emissions. PHOTO: SIMON SIMARD

Fertilizers are also heavy pollutants. Voigt says that half of what gets poured or sprayed onto the soil ends up in the water and air. In fact, soil bacteria convert a good amount of fertilizer’s artificial ammonia into nitric oxide, which is “almost 300 times worse than carbon dioxide as a greenhouse gas,” he says.

Voigt’s challenge, therefore, is to develop a different way to feed nitrogen to crops. Ultimately, his answer was to reconstruct the genes of nitrogen-fixing soil bacteria “from the ground up” to get the microbes to coat the roots of the plant as it grows. Then, as the bacteria convert nitrogen gas in the soil into ammonia, the plant can take it up directly. This is the work that he and his team are championing at MIT.

Since joining the Institute, Voigt has found ways to create variations on nitrogen fixation, allowing him to transfer the pathway to different bacterial species that are easier to manipulate. Currently, a set of his modified microbes are mixed in with corn seeds just before they’re planted in the soil. They supply the plants with 20% to 40% of their nitrogen, dramatically reducing the amount of fertilizer needed.

He has also altered Azorhizobium caulinodans—a bacterial species that does a particularly good job at grabbing onto nitrogen in the air—to ramp up nitrogen fixation in the presence of certain chemicals. After one of his collaborators engineered barley to produce and release those chemicals, Voigt helped demonstrate how the altered plant attracted A. caulinodans to colonize its roots where it then accelerated the fixing of nitrogen.

Scaling up farming sustainability

In 2011, Voigt and two of his students spun out a company, Pivot Bio, to license and scale up the technology and bring it to commercial farms across the United States. “It’s now a multibillion-dollar company,” says Voigt. Their product is used on about five million acres of farmland in this country, amounting to about 6% of the US corn crop.

Voigt is leading one of the projects in MIT’s Climate Grand Challenges (CGC), an Institute-wide effort launched in 2020 to mobilize the research community around unsolved climate problems. After more than 100 letters of interest from faculty, five projects were chosen for support, all of them offering interdisciplinary solutions and plans for rapid and large-scale implementation. Voigt’s team seeks to revolutionize agriculture by improving nitrogen distribution within plants, enhancing seed coatings to keep bacteria alive for longer, and fortifying crops to withstand climate change.

To Voigt, the CGC funding provides an opportunity to tackle the next phase of the nitrogen fixation problem. He plans to work with “more complex microbes that can fix nitrogen over a wider range of conditions, create genetic sensors that control the process so that it occurs only when it’s close to the root and not in the soil, and ramp up the overall amounts of nitrogen supplied through this technique.”

Voigt traveled to Kenya with students in the summer of 2023 to see nitrogen fixation technology in action. One of the first things he noticed was that fences are used to keep out hippos. He also noted a “dramatic difference” between the crops with the enhanced microbes (healthier, stronger stems) and those without. “The root systems are completely different when you pull them up,” he says.

The future of food production

Voigt expects that within the next three years, modified bacteria will be able to supply plants with 60% to 70% of the nitrogen they need, with the ultimate goal of dropping the microbes altogether. He ultimately wants to genetically engineer corn and other plants to free them from their bacterial leash, allowing them to fix nitrogen on their own. This would require moving the microbial genes into the cereal crops.

Voigt and his team have been trying to create such “self-fertilizing” plants for eight years, inspired by a vision of feeding millions of people on the planet while generating less pollution. “I feel like we’re getting close,” he says.

Read more: The Climate Project at MIT