Sulfur-driven approaches to cadmium detoxification: From soil microbials to plant-based mechanisms

Abstract

Plants easily absorb cadmium (Cd), a common and extremely poisonous element found in soils that poses a risk to human health and ecosystems. Through chemical and biological processes, sulfur (S), an important nutrient, reduces the hazards associated with Cd. By creating insoluble cadmium sulfide (CdS) precipitates and improving microbial immobilization, it lowers Cd mobility. Sulfate-reducing bacteria (SRB) transform sulfate into sulfide, precipitating Cd as CdS, whereas sulfur-oxidizing bacteria (SOB) increase the solubility of Cd by oxidation. Cd mobility is controlled by the SRB-SOB redox balance, while Cd immobilization or mobilization is deeply influenced by pH and Eh (redox potential). Sulfur treatment strengthens the iron-manganese oxides on root surfaces that act as a barrier to Cd migration. Sulfur also promotes vacuolar compartmentalization, chelation, and Cd binding to the root cell wall, all of which lower the concentration of free Cd ions. Sulfur increases the production of S-containing substances in plants, such as glutathione and phytochelatins, which chelate Cd. Additionally, S increases antioxidant capacity to reduce Cd toxicity in plants. Furthermore, S regulates Cd transporter proteins (e.g., HMA3, Nramp5) expression, controlling Cd translocation in plants. Distinct from prior studies that examine microbial or plant mechanisms in isolation, this work integrates them into a unified soil-microbe-plant continuum, providing new insights into the processes of sulfur’s role in Cd detoxification. The proposed S-driven approaches mitigate Cd hazard and shift the focus toward evaluating the long-term ecological impacts of S-Cd interactions, emphasizing soil health, plant productivity, and environmental sustainability.

Topics & Concepts