Improving the ability of nitrogen-fixing bacteria to colonize soybean roots is the aim of researchers at South Dakota State University's new Biofilm Science and Engineering Center. Researchers seek to leverage the bacteria to reduce the need for chemical fertilizer.

“Nitrogen-fixing bacteria must compete with thousands of other bacteria to colonize soybean roots,” said Sen Subramanian, an associate professor at South Dakota State University.

His research spans the departments of biology, microbiology, agronomy, horticulture and plant science. He will lead a research team with Zhengrong Gu, an associate professor at the university’s department of agricultural and biosystems engineering.

When soybean seeds are inoculated with nitrogen-fixing bacteria, only 50 percent of the soybean-plant nodules are occupied by inoculant strains, Subramanian said.

“Our focus is to make the inoculant strains more competitive in colonizing plants,” he said.

The research is being conducted to understand the fundamental interaction between microbes, which form communities known as biofilms. Researchers also will study the surfaces to which they adhere, said Robb Winter, a professor of chemical and biological engineering at the South Dakota School of Mines and Technology. He will lead the new biofilms-research center. The team from the mines school will investigate sulfate-reducing bacteria that corrode metals.

The crux of both projects is how surface properties affect bacteria attachment and biofilm formation. Subramanian plans to use the material as a substrate to which nitrogen-fixing bacteria can attach. Gu, whose expertise is in graphene, will formulate substrates using fabrication equipment. A new submicron three-dimensional printer will allow researchers to build specialized microfluidic chambers to observe nitrogen-fixing bacteria colonizing soybean roots.

Researchers also will study genetics associated with microbe attachment, with support from the South Dakota State University Genomics Sequencing Center. Visit for more information.

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