NSF funds research on nitrogen fixation

Himadri Pakrasi
Himadri Pakrasi (left), the Glassberg Greensfelder Distinguished University Professor and
Annesha Sengupta, a visiting graduate student, pictured in a growth chamber with flask containing cyanobacteria. (Photo: Joe Angeles/Washington University)

The word agriculture conjures up an array of images: endless fields of corn stalks, amber waves of grain, the deserts of Africa… Africa? While thoughts of the African landscape may tend to invoke a dry and empty countryside, scientists at Washington University in St. Louis are working to develop self-sustaining plants that could eventually turn the Sahara into a sea of green.

Himadri B. Pakrasi, the Glassberg Greensfelder Distinguished University Professor in the department of biology in Arts & Sciences and director of the International Center for Energy, Environment and Sustainability (InCEES), and Costas D. Maranas, professor of chemical engineering at Penn State, were recently awarded a $1.2-million grant from the National Science Foundation for their collaborative study of systems biology. Specifically, the Pakrasi and Maranas labs hope to decode the inner workings of cyanobacteria for the ultimate purpose of producing nitrogen-fixing crop plants.

Photo of Himadri Pakrasi's Lab

Researchers engineer bacteria that create fertilizer out of thin air

For more than a century, farmers around the world have relied heavily on chemical fertilizers to help grow their plants and crops. Fertilizers contain nitrogen, an essential building block for all life forms to grow, and an element that is abundant in the earth’s atmosphere. However, creating man-made fertilizers is an energy intensive process that contributes to greenhouse gases and leads to run-off issues that severely damage the environment. A solution to this problem is to engineer plants to absorb nitrogen from the atmosphere and convert it into fertilizer, a process known as nitrogen fixation, so that the plants would become self-sufficient.

“If you have engineered seeds that you give to an African farmer, that farmer can then plant the seeds, which gives rise to a field of crops that would not need chemically synthesized fertilizer to grow,” Pakrasi said. “This has huge agricultural implications – not just for the affluent, Western world, but to the areas hardest hit by climate change.”

Easier said than done. Nitrogen fixation cannot take place in the cells of most photosynthetic organisms – plants that convert sunlight into energy – because when plants are undergoing photosynthesis, a byproduct is oxygen. And oxygen is like a poison when it mixes with nitrogenease, the enzyme that enables nitrogen fixation. However, there is an organism that can accommodate both photosynthesis and nitrogen fixation in the same cell: cyanobacteria.

Just like human beings, cyanobacteria have a robust circadian rhythm – a 24-hour biological cycle – during which they photosynthesize in the day and fix nitrogen at night. Scientists have long studied these bluish-green creatures, but do not have a detailed understanding of how circadian rhythms allow cyanobacteria to adjust its metabolism for both nitrogen fixation and photosynthesis to take place in the same cell. With advances in genetic modification tools, it is now possible to probe deeper into the details of this process.

“There are still missing parts of the cyanobacterial puzzle,” Pakrasi said. “The only way to identify what those missing parts are is to actually go into the cyanobacterium and tease apart the machinery. And that’s what this grant will allow us to do.”

In other words, the Pakrasi lab will perform a series of genetic modifications to the cyanobacteria and generate new data. The Maranas lab will then take the data and develop a predictive model for the inner working of the cyanobacterium. This iterative process will take some time, but the research is imperative to combating the climate changes facing the planet, Pakrasi said.

“It’s kind of like building an electric pickup truck,” Pakrasi said. “How do you go from a gasoline fueled car to a Tesla pickup truck? The basic technology for making a gas fueled car is already known, but we’re moving to a new paradigm of production in the form of a Tesla truck. Once we figure it out, we can deploy the new technology to our partners all over the world.”

Funding: This grant was organized by InCEES at Washington University in St. Louis.

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