Drought-tolerant Streptomyces pactum Act12 assist phytoremediation of cadmium-contaminated soil by Amaranthus hypochondriacus: great potential application in arid/semi-arid areas.

Microbe-assisted phytoremediation provides an effective approach to clean up heavy metal-contaminated soils. However, severe drought may affect the function of microbes in arid/semi-arid areas. Streptomyces pactum Act12 is a drought-tolerant soil actinomycete strain isolated from an extreme environment on the Qinghai-Tibet Plateau, China. In this study, pot experiments were conducted to assess the effect of Act12 on Cd tolerance, uptake, and accumulation in amaranth (Amaranthus hypochondriacus) under water deficit. Inoculated plants had higher Cd concentrations (root 8.7-33.9 %; shoot 53.2-102.1 %) and uptake (root 19.9-95.3 %; shoot 110.6-170.1 %) than non-inoculated controls in Cd-treated soil. The translocation factor of Cd from roots to shoots was increased by 14.2-75 % in inoculated plants, while the bioconcentration factor of Cd in roots and shoots was increased by 10.2-64.4 and 53.9-114.8 %, respectively. Moreover, inoculation with Act12 increased plant height, root length, and shoot biomass of amaranth in Cd-treated soil compared to non-inoculated controls. Physiochemical analysis revealed that Act12 enhanced Cd tolerance in the plants by increasing glutathione, elevating superoxide dismutase and catalase activities, as well as reducing malondialdehyde content in the leaves. The drought-tolerant actinomycete strain Act12 can enhance the phytoremediation efficiency of amaranth for Cd-contaminated soils under water deficit, exhibiting potential for application in arid and semi-arid areas.