Poly-γ-glutamic acid, a bio-chelator, alleviates the toxicity of Cd and Pb in the soil and promotes the establishment of healthy Cucumis sativus L. seedling.

Poly-γ-glutamic acid (γ-PGA) can be used as a chemical stabilizer to chelate heavy metals in polluted soils. We investigated the effects of γ-PGA on cucumber seedlings under Cd and Pb stresses. γ-PGA effectively reduced the growth inhibitory effects of Cd and Pb on cucumber seedlings. Cd and Pb absorption in cucumber seedlings was also decreased. Further, γ-PGA decreased the malondialdehyde content, and increased the proline content and the total antioxidant capacity of cucumber seedlings in a dose-dependent manner. Infrared spectral characterization of γ-PGA-Cd and γ-PGA-Pb showed that Cd2+ and Pb2+ bind to free carboxyl groups on γ-PGA. Furthermore, γ-PGA-Cd and γ-PGA-Pb were degraded by 22.02 and 24.68%, respectively, within 28 weeks. The chelating rate of γ-PGA-Pb and γ-PGA-Cd reached 27.26 and 14.28%, respectively. Further, γ-PGA alleviated the negative effects of Cd and Pb on soil microorganisms. Thus, γ-PGA can effectively reduce the accumulation of heavy metals in crops caused by heavy metal pollution of farmland, and has significant application value.