Engineering rhizosphere bacteria for improved cadmium bioremediation efficacy

Soil cadmium (Cd2+) pollution poses a significant environmental threat due to its persistence, toxicity, and potential for bioaccumulation in the food chains. Rhizosphere bacteria, forming a critical plant-microbe interface, play a key role in mediating metal acquisition and detoxification. Genetically modifying these naturally occurring microorganisms offers a promising approach to enhance Cd2+ bioremediation efficiency. This review focuses on molecular techniques for engineering rhizosphere bacteria to improve Cd2+ tolerance, increase metal sequestration, and enhance plant growth promotion capabilities. It explores the genetic potential of microorganisms for developing sustainable and efficient Cd2+ detoxification technologies in soil. Key advances discussed in the current review for the application of genetically engineered rhizosphere bacteria (ERB) for Cd2+ bioremediation include (i) increased Cd2+ adsorption and accumulation with the focus on modifying bacterial metal transporters and on the expression of metal-binding proteins that increase Cd2+ uptake, intracellular sequestration, and detoxification; and (ii) enhanced rhizosphere competence and synergistic PGP for combined bio- and phytoremediation. This approach focuses on genetic enhancement of chemotaxis to improve bacterial colonization persistence and effectiveness in the rhizosphere, as well as the development of co-engineered bacteria with PGP traits that generate synergistic effects.