New research helps reduce arsenic absorption in rice plants.

Researchers at the University of Delaware (USA) have discovered a type of soil bacteria capable of creating an "iron shield" that helps prevent arsenic absorption in rice plants.

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

A University of Delaware experiment demonstrated the effects of the bacterium EA106 (On the far left is the control rice crop, neither treated with EA106 nor arsenic. Rice treated with EA106 showed superior growth, while rice treated with arsenic was stunted and had yellow leaves. On the far right, rice treated with arsenic recovered when its roots were inoculated with EA106).

Harsh Bais, Associate Professor of Soil and Plant Sciences and lead researcher at the University of Delaware, conducted the study. Funded by the National Science Foundation, the research was subsequently published in the international journal Planta. His collaborators included Professors Angelia Seyfferth, Janine Sherrier, Venkatachalam Lakshmanan, Gang Li, and Deepak Shantharaj, all of whom are currently employed in the Department of Soil and Plant Sciences at the University of Delaware.Research from the University of Delaware has offered the prospect of a low-cost biological solution: a microbial preparation for rice that helps protect this vital food source from accumulating to toxic levels of arsenic – one of the world's leading toxins. Rice is currently a staple in the meals of more than half the world's population.

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

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

While rice absorbs phosphate, a nutrient essential for growth, it also absorbs arsenic – a substance with a similar chemical structure to phosphate. “This particular bacterium, EA106, is very effective at mobilizing iron, thereby preventing the rice from absorbing arsenic,” Bais explained. “An iron deposit on the root surface will hinder arsenic absorption into the rice plant.”

Researchers conducted experiments with hundreds of rice varieties, including both upland and lowland rice, in the University of Delaware's greenhouses. Introducing EA106 improved iron uptake in the plant roots while reducing arsenic accumulation in the plants.

EA106 bacteria and iron deposits are forming on the roots of rice plants.

Although the results are very promising, according to Bais, the next steps of the research will determine whether there is a viable natural solution to this problem. If the next step of the research is successful, there will be a low-cost technology to protect rice varieties using beneficial bacteria.

Furthermore, using EA106 to protect rice not only reduces arsenic absorption, but also helps increase the iron content in rice grains – a beneficial nutrient.

“I grew up near rice paddies in India, so I have a particular passion for this field,” Mr. Bais said. “Essentially, the smallholder farmers there don’t have much to feed their families. They cultivate 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 as well as for rice security worldwide.”

In another related study, Bais wanted to assess the ability of plants inoculated with EA106 to withstand other stresses, including both arsenic and rice blast disease, a fungus that can cause the loss of about 30% of the world's rice production each year.

Bais's team previously isolated a naturally occurring bacterium from rice soil that could attenuate rice blast disease. His team is now evaluating how a link between beneficial microorganisms and rice could enhance the crop's disease resistance.

According to the National Agricultural Extension Service