Surface Display of Multiple Metal-Binding Domains in Deinococcus radiodurans Alleviates Cadmium and Lead Toxicity in Rice

Cadmium (Cd) and lead (Pb) are the primary hazardous heavy metals that accumulate in crops and pose substantial risks to public health via the food chain. Limiting the migration of these toxic metals from contaminated environments to rice is the most direct and crucial remediation approach. Bioremediation with microorganisms has been extensively utilized for managing heavy metal contamination in the natural environment, and the interplay between microbes and crops is important to alleviate heavy metal stress. Here, we express Lpp-OmpA fused with two metal-binding domains (PbBD and MTT5) in the outer membrane of to enhance both Cd and Pb adsorption. Our results showed that the recombinant strain LOPM, which displayed an increased tolerance to both Cd and Pb stress, exhibited a 4.9-fold higher Cd adsorption and 3.2-fold higher Pb adsorption compared to wild-type strain R1. After LOPM cells colonized the rice root, Cd content reduced to 47.0% in root and 43.4% in shoot; Pb content reduced to 55.4% in root and 26.9% in shoot, as compared to the plant's exposure to Cd and Pb. In addition, cells of LOPM strain colonized on rice roots alleviate Cd- and Pb-induced oxidative stress by reducing ROS levels and enhancing antioxidant enzyme activities in rice. This study supplies a promising application of genetic-engineering extremophile bacteria in reducing heavy metal accumulation and toxicity in rice.