The Role of Ni and Cd-Resistant Rhizobacteria in Promotion of Rice Seedlings Growth and Alleviation Combined Phytotoxicity of Ni and Cd

Abstract The heavy metal compound pollution is becoming a serious problem in the environmental management. In the present study, we focused on the combined pollution of nickel (Ni) and cadmium (Cd) and isolated three Ni and Cd-resistant rhizobacteria (strains Y3, Y4 and Y5) with important PGP traits. According to 16S rDNA sequence homology, strains Y3, Y4 and Y5 were identified as Pseudomonas sp., Chryseobacterium sp. and Enterobacter sp., respectively. Then the effects of strains Y3, Y4 and Y5 on rice growth under the combined stress of Ni and Cd were examined. The results indicated that strains Y3, Y4 and Y5 enhanced the seed germination, biomass production and chlorophyll accumulation of rice seedling under compound stress of Ni and Cd. These strains also conferred rice tolerance to Ni and Cd by increasing antioxidant enzyme activity in seedlings. Furthermore, comparing among three strains, it was found that strain Y3 with stronger ability of IAA production, EPS production and ACC deaminase activity had the best promotion effect on rice growth under the combined stress of Ni and Cd. In addition, strain Y5 had better IAA production capacity and a better effect on the growth of rice roots than strain Y4 under Ni and Cd stress, which indicated that IAA production might play a particularly critical role in root growth under the stress of Ni and Cd.