New insights into the adaptation mechanisms of exopolysaccharide-producing Klebsiella pasteurii L72 to Cd2+ exposure

Cd²⁺ exposure poses a serious threat to ecological safety and human health. Certain bacterial species can produce exopolysaccharide (EPS) as a strategy for survival in such environments. A new EPS-producing strain was isolated from Cd-contaminated mine soil, exhibiting strong resistance to Cd²⁺ (up to 700 mg/mL) and excellent Cd²⁺ removal capacity (79.36% removal at a Cd²⁺ concentration of 200 mg/mL), and was identified as Klebsiella pasteurii L72 using genotypic data. It showed a remarkable increase in both EPS yield and uronic acid content under long-term exposure to 100–300 mg/mL Cd²⁺ concentrations. Multiple physicochemical analyses revealed that EPS functional groups such as C=O, N–H, and COOH were involved in Cd²⁺ adsorption by forming EPS-metal complexes. Genomic data identified a large number of functional genes related to Cd toxicity resistance and stress response. Transcriptomic profiling further confirmed that an adaptive response to Cd²⁺ up-regulated the expression of genes involved in sulfur metabolism, transmembrane transporters, and EPS synthesis. These results indicate that K. pasteurii L72 cells and EPS can be utilized as complex biosorbents for eliminating Cd²⁺ from polluted environments.