New research helps reduce arsenic absorption in rice plants

Researchers at the University of Daleware (USA) have discovered a type of soil bacteria that can create an "iron shield" to help prevent the absorption of arsenic in rice plants.

Arsenic occurs naturally in soil, air, water, plants and animals. It is used in many industrial products and activities, from wood preservation, pesticides, fertilizers to copper smelting. Long-term exposure to arsenic is thought to cause serious diseases such as cancer, cardiovascular disease, and diabetes.

University of Daleware experiment demonstrating the effects of EA106 bacteria (On the far left is the control rice that was not treated with EA106 or Arsenic. The EA106-treated rice showed superior growth while the Arsenic-treated rice was stunted and had yellow leaves. On the far right, the Arsenic-treated rice recovered when their roots were inoculated with EA106)

Harsh Bais, associate professor of plant and soil sciences, led the research team at the University of Delaware, which was funded by the National Science Foundation and published in the international journal Planta. His collaborators included professors Angelia Seyfferth, Janine Sherrier, Venkatachalam Lakshmanan, Gang Li and Deepak Shantharaj, all in the Department of Plant and Soil Sciences at the University of Delaware.Research from the University of Delaware has offered the prospect of a low-cost biological solution, a microbial inoculant for rice that could protect this important food source from accumulating toxic levels of arsenic, one of the world’s leading poisons. Rice is now a staple in the diet of more than half the world’s population.

The soil bacterium the scientists discovered was named “EA106” after former graduate student Emily Alff, who isolated it when she was a research student in Bais’ lab. EA106 was found in the roots of a North American rice variety grown commercially in California. It belongs to the gram-negative rod-shaped bacteria group Pantoea, which form yellow, slimy colonies on plant roots.

Because rice is grown in flooded fields, often in arsenic-laden water in hotspots like Bangladesh, India, and China, it absorbs 10 times more arsenic than other cereal grains like wheat and oats.

While rice absorbs phosphate, a nutrient needed for growth, it also absorbs arsenic, which has a similar chemical structure to phosphate. “This particular bacterium, EA106, is very efficient at mobilizing iron, which prevents arsenic from being absorbed by the rice,” Bais explains. “An iron plaque on the surface of the roots prevents arsenic from being absorbed into the rice plant.”

Researchers conducted experiments with hundreds of rice varieties, including both upland and paddy rice, in the University of Delaware greenhouse. Inoculation with EA106 improved iron uptake in the roots while reducing the accumulation of toxic arsenic in the plants.

EA106 bacteria and iron plaque are forming on rice roots.

While the results are promising, Bais said the next steps of the research will determine whether there is a viable natural solution to the problem. If the next step of the research is successful, it could lead to a low-cost technology that can protect rice plants with beneficial bacteria.

In addition, using EA106 to protect rice not only reduces arsenic absorption, it also helps increase iron content in rice grains – a beneficial nutrient.

“I grew up near rice fields in India, so I have a special passion for this area,” said Bais. “Basically, smallholder farmers there don’t have much to feed their families. They grow rice in small plots where there is a lot of arsenic in the soil and water. The work we are doing is very important for them and for rice security around the world.”

In other related research, Bais wants to evaluate the ability of EA106-inoculated plants to withstand other stresses, from both arsenic and rice blast, a fungus that can wipe out about 30 percent of the world's rice crop each year.

Bais’s group previously isolated a naturally occurring bacterium from rice soil that attenuates rice blast. His team is now evaluating how a link between beneficial microbes and rice could increase the plant’s disease resistance.

According to National Agricultural Extension