Growth and Cadmium Accumulation of Solanum nigrum L. Seedling were Enhanced by Heavy Metal-Tolerant Strains of Pseudomonas aeruginosa

Abstract

Some heavy metal-tolerant bacteria recognized as plant growth-promoting bacteria (PGPB) could improve plant growth. Here, the growth and Cd accumulation of Solanum nigrum seedling inoculated by soaking the roots in a dilute suspension of the Cd-tolerant strains ZGKD5 or ZGKD2 were investigated. The results showed that both ZGKD5 and ZGKD2 exhibited the characterization of producing IAA, siderophores, ammonia, and biosurfactant, and solubilizing phosphate and fixing nitrogen. The siderophores produced by both strains could chelate various heavy metals, such as Cu, Cd, Zn, and Ni. The shoot height, root length, number of fibrous root, and dry weight of S. nigrum seedling were significantly increased by inoculation with ZGKD5 or ZGKD2 in the absence or presence of Cd stress. The Cd concentration and translocation from root to shoot in seedlings were remarkably increased, indicating that both strains could improve the growth and Cd phytoextraction of S. nigrum. The activities of SOD, POD, CAT, and APX in both inoculated and uninoculated plants were increased under Cd stress, indicating that these antioxidative enzymes could alleviate oxidative stress induced by Cd. Furthermore, activities of antioxidative enzyme in inoculated plants exposed to Cd stress was lower than that in uninoculated Cd-stressed plants, which might be due to the decreasing metabolism caused by high levels of Cd. These results indicated that strains ZGKD5 and ZGKD2 are PGPB and have the potential for improving the phytoremediation of S. nigrum in Cd-contaminated farmland soil.