Engineered Soil Microbe Offers Dual Benefits for Soil Remediation and Rice Protection

A bioengineering strategy to reduce toxic cadmium levels in rice was successfully demonstrated by researchers at the Hunan Academy of Agricultural Sciences. By modifying the beneficial soil bacterium Citrobacter sp. XT1-2-2 to overexpress key genes such as cysH and cysJ, which are responsible for encoding sulfate assimilation enzymes, the team created strains that help trap heavy metals right at the root zone. Inoculating rice plants with these modified bacteria reduced the level of available cadmium in the surrounding soil while lowering cadmium accumulation in rice roots.

DNA from the root-zone microbes were analyzed to assess how the treatment altered the soil ecosystem. The engineered soil bacterium increased the overall diversity and richness of both bacterial and fungal communities as useful bacterial groups like Bacillota and Pseudomonadota became more abundant, alongside beneficial fungi like Ascomycota. The modified bacteria helped recruit a microbial network that accelerated sulfate breakdown and converted soluble cadmium into solid, insoluble compounds directly on the root surface. This process created a physical shield that blocked the toxic metal from entering the plant's vascular system.

At the protein level, cell wall-reinforcing proteins, such as extensins and chitinases, increased to help lock cadmium ions out of the main transport system. Simultaneously, stress-related root enzymes were reduced, confirming that protection against heavy metal stress was conferred by the engineered bacteria. With these findings, scientists could potentially anchor on this approach to develop sustainable, microbe-based strategies that clean up farmland while protecting staple food crops.

Read the full study in BMC Genomics to learn more.