Improving cadmium mobilization by phosphate-solubilizing bacteria via regulating organic acids metabolism with...

Organic acids secreted by phosphorus-solubilizing bacteria (PSB) is one of the main biological metabolites with cadmium (Cd) mobilization capacity in the conversion of insoluble precipitate forms to bioavailable forms in contaminated soil. However, the fluctuating concentrations of nutrient elements caused by agricultural activities may result in the substantial variances of carbohydrate metabolism of microorganisms involved in Cd remediation, it is therefore essential to study how metabolic strategies, especially for organic acids, affected by the environmentally friendly fertilizers, such as potassium (K). In this study, adding K⁺ (KCl) concentrations from 0.0 to 100.0 mg/L in medium clearly accelerated Cd mobilization from 15.9 to 35.9 mg/L via inducing the secretion of tartaric acid, 3-hydroxybutyrate, fumaric and succinic acids, increased by 10.0-, 7.5-, 4.3- and 4.1-fold changes, respectively. Current data revealed that the significant differences of metabolic pathways and genes expressions with the varied K⁺ concentrations included: ⅰ) K⁺ induces a substantial up-regulation in metabolic pathway of pyruvic acid to oxaloacetate and tartaric acids; ⅱ) the varied expression of genes involved in encoding enzymes of tricarboxylic acid cycle result in the up-regulated fumaric acid, succinic acid and 3-hydroxybutyrate; ⅲ) the expression of genes related enzyme cysteine and glutamate metabolism processes promoted with the increasing bioavailable Cd concentrations. Besides, P-type ATPase activity increased with K⁺ levels, indicating that H⁺ efflux and medium acidification were strengthened. In general, an appropriate enhancement of K based fertilizer is an effective manner for soil Cd remediation via the regulation of organic acids metabolism and H⁺ secretion of PSB.