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Wash U scientists aim to engineer self-fertilizing plants

Washington University biologists holding a glass jar containing bacteria that have been engineered to use nitrogen from the atmosphere to help it grow.
Joe Angeles | Washington University
Himadri Pakrasi, on left, led a team of researchers who engineered a species of bacteria to use nitrogen from the atmosphere to help it grow. The research could help scientists genetically engineer crops to do the same and reduce fertilizer use.

Someday, farmers may no longer need to use fertilizer for their crops. Researchers at Washington University in St. Louis have recently made a crucial step toward engineering plants to fertilize themselves.

Plants need nitrogen to grow, and, in nature, they absorb the nutrient from dead plants. In agriculture, farmers apply fertilizer, as crops alone cannot convert nitrogen from the air into ammonia. Because fertilizer pollutes the environment and is costly for farmers in developing countries, scientists have long researched ways to engineer plants to convert nitrogen by themselves.

In the journal mBio, Wash U researchers reported that they’ve genetically engineered a species of bacteria to use nitrogen from the air to grow.

The research was funded by a $2.3-million grant from the National Science Foundation.

“We’ve made significant progress toward solving this big problem,” said Himadri Pakrasi, a biologist and director of Washington University’s International Center for Energy, Environment and Sustainability.

But achieving that result in plants has been challenging, Pakrasi added.

Plants turn sunlight into food through photosynthesis, which produces oxygen. But oxygen kills the enzymes that would help plants convert nitrogen from the air into nutrients, and that has made it difficult to engineer plants that can fertilize themselves, Pakrasi said.

He and his colleagues identified a species of bacteria that’s able to convert nitrogen from the air and transferred the genes linked to that ability into another bacteria species that cannot convert nitrogen. The researchers also engineered the bacteria to produce oxygen during the day and nitrogen at night.

The researchers were successful in engineering the bacteria to self-fertilize at a high rate and want to collaborate with scientists who have plant-engineering expertise to advance the research.

However, showing that nitrogen-converting genes could be transferred in bacteria is not new. Scientists first demonstrated that in the 1970s.

But it’s been challenging to engineer plants to do the same, said Allen Good, a biologist at the University of Alberta. Progress has been slow partly due to lack of funding and uncoordinated research efforts. But most importantly, the process of engineering a plant to produce nitrogen-fixing enzymes is much more complicated than engineering a plant to be herbicide-tolerant, he said.

“One has the complexity of an abacus; The other’s [got] the complexity of a Watson computer,” Good said.

Engineering plants that could receive its nitrogen from the air could make a huge difference in cleaning up the environment by cutting down the amount of fertilizer used by farms. Fertilizer use contributes to nitrogen pollution in waterways that create algal blooms and dead zones. It also exacerbates climate change by releasing large amounts of nitrous oxide, a greenhouse gas that has a worse impact than carbon dioxide. Fertilizer can be particularly expensive for farmers in Asia, Africa and South America, Pakrasi said.

“If they have seeds that give rise plants that can fix their own nitrogen,” he said, “then the agricultural productivity is estimated to go up by four to five folds. Right now, the productivity is very, very low.”

Follow Eli on Twitter: @StoriesByEli

Eli is the science and environment reporter at St. Louis Public Radio.