Newswise — Chemical fertilizer production accounts for about 1.5 percent of global greenhouse gas emissions. MIT chemists hope to help reduce this carbon footprint by replacing certain chemical fertilizers with a more sustainable source: bacteria.
Bacteria capable of converting nitrogen gas into ammonia could not only provide the nutrients plants need, but also help regenerate soil and protect plants from pests. However, these bacteria are sensitive to heat and humidity, making it difficult to scale up their manufacturing and ship them to farms.
To overcome this obstacle, MIT chemical engineers designed an organometallic coating that protects bacterial cells from damage without hindering their growth or function. In a new study, they found that these coated bacteria improved the germination rate of a variety of seeds, including vegetables like corn and bok choy.
This coating could make it much easier for farmers to deploy microbes as fertilizer, says Ariel Furst, the Paul M. Cook Career Development Assistant Professor of Chemical Engineering at MIT and senior author of the study.
“We can protect them from the drying process, which would allow us to distribute them much more easily and cheaply, because they are in dried powder form rather than liquid,” she says. “They can also withstand heat up to 132 degrees Fahrenheit, which means you won’t need to use cold storage for these microbes.”
Benjamin Burke ’23 and Gang Fan, postdoctoral fellows, are lead authors of the paper, which appears in the Journal of the American Chemical Society Au. Pris Wasuwanich and Evan Moore ’23, undergraduate students at MIT, are also authors of the study.
Chemical fertilizers are made using an energy-intensive process known as Haber-Bosch, which uses extremely high pressures to combine nitrogen from the air with hydrogen to produce hydrogen. ammonia.
Besides the large carbon footprint of this process, another disadvantage of chemical fertilizers is that their long-term use eventually depletes soil nutrients. To help restore soils, some farmers have turned to “regenerative agriculture,” which uses various strategies, including crop rotation and composting, to keep soils healthy. Nitrogen-fixing bacteria, which convert nitrogen gas into ammonia, can facilitate this approach.
Some farmers have already started deploying these “microbial fertilizers,” growing them in large fermenters on site before applying them to the soil. However, this represents a prohibitive cost for many farmers.
Sending these bacteria to rural areas is currently not a viable option, as they are susceptible to heat damage. The microbes are also too delicate to survive the freeze-drying process that would make them easier to transport.
To protect the microbes from heat and freeze-drying, Furst decided to apply a coating called metal-phenol network (MPN), which she previously developed to encapsulate microbes for other uses, such as protecting therapeutic bacteria delivered to the digestive tract.
The coatings contain two components – a metal and an organic compound called a polyphenol – that can self-assemble to form a protective shell. Metals used for coatings, including iron, manganese, aluminum and zinc, are considered safe as food additives. Polyphenols, often found in plants, include molecules such as tannins and other antioxidants. The FDA classifies many of these polyphenols as GRAS (generally considered safe).
“We use these natural, food-grade compounds that are known to have benefits on their own, and then they form these little pieces of armor that protect the microbes,” Furst says.
For this study, the researchers created 12 different MPNs and used them to encapsulate Pseudomonas chlororaphis, a nitrogen-fixing bacteria that also protects plants against harmful fungi and other pests. They found that all the coatings protected the bacteria from temperatures up to 50 degrees Celsius (122 degrees Fahrenheit), as well as relative humidity up to 48 percent. The coatings also kept microbes alive during the freeze-drying process.
A helping hand for seeds
Using microbes coated with the most effective MPN – a combination of manganese and a polyphenol called epigallocatechin gallate (EGCG) – the researchers tested their ability to help seeds germinate in a laboratory dish. They heated the coated microbes to 50°C before placing them in the dish and compared them to fresh uncoated microbes and freeze-dried uncoated microbes.
The researchers found that the coated microbes improved seed germination rates by 150 percent, compared to seeds treated with fresh, uncoated microbes. This result was consistent across several seed types, including dill, corn, radishes, and bok choy.
Furst created a company called Seia Bio to commercialize the coated bacteria for large-scale use in regenerative agriculture. She hopes the low cost of the manufacturing process will help make microbial fertilizers accessible to small farmers who don’t have the fermenters needed to cultivate such microbes.
“When we think about developing technology, we have to intentionally design it to be inexpensive and accessible, and that’s what this technology is. This would help democratize regenerative agriculture,” she says.
The research was funded by the Army Research Office, a National Institutes of Health New Innovator Award, a National Institute for Environmental Health Sciences Core Center grant, the CIFAR Azrieli Global Scholars Program, the MIT J-Program WAFS, the MIT Climate and Sustainability Consortium. , and the MIT Deshpande Center.