Low-Cost, Eco-Friendly Fertilizers from Bacteria

A row of seedlings growing in stages from newest to oldest

For the last hundred years, farmers have provided plants with much-needed nitrogen in the form of ammonia fertilizer, which they synthesize through a process that uses natural gas and nitrogen derived from air. While effective, the process has its downfalls: It releases large amounts of carbon dioxide into the atmosphere and accounts for 1-2 percent of all global energy use.

Now, a team of University of Minnesota scientists is working on a sustainable alternative. Led by Brett Barney, Ph.D., assistant professor of bioproducts and biosystems engineering with the U’s College of Food, Agricultural and Natural Resource Sciences, the team is genetically editing a type of bacteria that naturally produces nitrogen to make it produce a much greater amount of the nutrient. That nitrogen, in turn, will fertilize the soil and steadily supply crops with the nutrients they need to thrive. Ultimately, the team aims to develop a new standard for supplying Minnesota’s key crops — like corn and wheat — with reliable nutrition to meet the growing demand for food, while curbing the environmental side effects of injecting ammonia-based fertilizers into the soil.

The project is part of the state-funded MnDRIVE Transdisciplinary Research Program, where researchers from different departments work beyond the limits of their disciplines to address complex challenges.

“In nature, these bacteria are independent microbes that happen to provide only slight benefits to the plants around them as a side effect of their own metabolism or eventual death,” Barney said. “What we’re trying to do is tweak the bacteria to more efficiently produce this nitrogen that can serve as natural fertilizer, essentially forming a partnership between the bacteria and the crops they support. All of our experiments are showing that the potential is there.”

On their own, these “nitrogen-fixing” bacteria — which pull nitrogen from the air and convert it into various nitrogen products — supply too little fertilizer to support crop growth. But by removing specific parts of the bacteria’s genetic code, Barney and his team can block certain processes in how the bacteria break down waste material, resulting in a build-up of excess nitrogen that the bacteria eventually release into the soil. In the lab, Barney has been able to determine which bacterial test colonies best produce high levels of nitrogen through the use of a biosensor he designed that turns blue when nitrogen compounds are present.

Barney and his team have already succeeded in getting nitrogen-fixing bacteria to fertilize water-based plants like algae. Results of these studies, recently published in Applied and Environmental Microbiology, were used as “proof of concept” for the potential of doing similar projects with conventional crops.

Why work to develop a bacteria-based fertilizer when farmers can use ammonia? One reason is that it can save farmers money, replacing the high cost of transporting and handling ammonia fertilizer on its way from the production plant to the farm with the lower cost of shipping live bacterial cultures.

There are also environmental benefits. Unlike ammonia fertilizer that is injected into the soil, the researchers hope to make the bacteria produce nitrogen as compounds with lowered solubility, making it less likely to wash away from fields and contaminate nearby waterways. Industrial nitrogen production also contributes to climate change, as it contributes to the levels of carbon dioxide in the atmosphere, according to the Environmental Protection Agency.

Finally, there’s the safety component: While the bacteria are harmless to humans, ammonia in its gas form can irritate the eyes, nose, skin and throat, and even be fatal if inhaled in high concentrations, according to the Centers for Disease Control and Prevention.

A Field Full of Variables

While fertilizing a field through bacteria is an exciting prospect, it will take extensive experimentation to find the ideal conditions that help plants thrive.

Craig Sheaffer, Ph.D., professor of agronomy and plant genetics, is leading the effort to move the bacteria out of the lab and into real soil, but adapting that process to land-based plants poses a challenge. Before any testing can happen in actual fields, Sheaffer will run experiments in controlled greenhouses to understand how different variables affect the plant’s growth, like the type of soil used, the amount of oxygen available and, of course, the type of genetically modified bacteria used.

The researchers will also examine how well this type of bacteria can stay in the soil before needing to be reapplied. The findings will help them decide whether it’s best to apply the bacteria when tilling a field, or if there’s a more effective way to ensure the bacteria take hold, such as by selling farmers pre-treated packages of soil. The bacteria may need to be applied several times in succession before they begin to last longer and treatments can become less frequent, Barney said. If, on the other hand, the bacteria prove highly efficient and try to make too much nitrogen, the limited food supply available to them in the soil will prevent them from overproducing.

If successful, Sheaffer said bacteria-based fertilizers would be appealing to farmers who are looking to cut down on both shipping costs and runoff. But it may prove especially interesting to organic crop farmers, who are unable to inject ammonia into their fields but still need to supply nutrients to their crops.

“They still need a good source of nitrogen to gain high growing yields,” Sheaffer said. “If this technology works in the field, you can imagine how important it would be to organic farmers.”

Collaborating for Healthier Crops

As Barney works on editing the bacteria’s genetics and Sheaffer monitors progress in the greenhouse, their fellow researchers are digging into other aspects of the project.

Neil Olzewski, Ph.D., professor of plant biology with the College of Biological Sciences, is leading studies with model plant systems to determine the potential to increase available carbon from the root systems. Increased carbon would enhance the ability of the bacteria to grow in close association with the plants it is fertilizing. Further studies to determine the potential to utilize stover and wheat straw are being done by students in Barney’s lab along with assistance from Sheaffer.

As the technology comes together, Gary Sands, a professor of bioproducts and biosystems engineering like Barney, will investigate how to transition the biofertilizer technology from the development phase to actual farms, where Minnesota’s farmers can put it to use.

While the experiments are still in the early stages, Barney and Sheaffer anticipate the team will see significant progress following upcoming tests in the greenhouse this summer.

“This project illustrates how applying technology to a very practical problem can have huge benefits for agriculture,” Sheaffer said. “I’m excited that MnDRIVE has invested in this.”

This project is supported by MnDRIVE, a landmark partnership between the university and the state of Minnesota that aligns areas of university strength with the state’s key and emerging industries to advance new discoveries that address grand challenges.