Pyoverdine-deficient mutant Pseudomonas umsongensis CR14ΔpvdA enhances cadmium immobilization by regulating genes and metabolites related to cell wall/membrane biosynthesis and transcription factors

Cadmium (Cd) pollution poses a significant global environmental threat. This study elucidates the molecular mechanisms by which the pyoverdine-producing pvdA gene deletion mutant Pseudomonas umsongensis CR14ΔpvdA (ΔpvdAM) enhances Cd immobilization in a Cd-containing solution. Transcriptomic analysis revealed that, compared to the wild-type CR14, the ΔpvdAM significantly upregulated genes related to lipopolysaccharide biosynthesis, periplasmic proteins, and transcription factors, while downregulating the membrane integrity-associated gene tolA. Metabolomic analysis further identified upregulated intracellular metabolites in the ΔpvdAM, including D-glyceraldehyde, acetyl-CoA, glycerol 3-phosphate, phosphatidylethanolamine, phosphatidic acid, and several amino acids, all involved in cell wall/membrane assembly, compared with those in strain CR14. RTqPCR confirmed the upregulated expression levels of Cd immobilization-related genes 4779, hmgL, phoP, and 3634 in the ΔpvdAM compared with those in strain CR14 under both Cd-free and Cd-stressed conditions. Functional validation via gene knockout demonstrated that mutants CR14ΔhmgL, CR14ΔphoP, CR14Δ3634, and CR14Δ44779 significantly increased solution Cd concentrations by 46 %-167 %, whereas the CR14ΔtolA mutant decreased solution Cd by 38 % after 60 h of incubation compared with strain CR14. Our findings indicate that the ΔpvdAM enhances Cd stabilization by coordinately regulating genes and metabolites pivotal for cell surface adsorption and intracellular accumulation, providing novel insights into bacterial Cd immobilization mechanisms.