Insight into the mechanisms of Cd(II) on significantly enhancing rhizobacterial ACC deaminase activity in Cd-resistant Ensifer morelensis A23T

Plant growth-promoting rhizobacteria that are resistant to cadmium (Cd) have garnered significant attention in Cd2+ remediation owing to their dual capabilities of mitigating heavy metal stress and enhancing plant growth. A rhizobacterial strain with a high level of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase was isolated from a sample of soil contaminated with Cd2+ and identified as Ensifer morelensis A23T based on its genotype. In particular, the ACC deaminase activity of strain A23T was significantly enhanced when exposed to 50 mg L-1 Cd2+. Genomic data from this strain identified a large number of functional genes involved in the tolerance of Cd2+ and the promotion of plant growth. Transcriptomic profiling confirmed significant upregulation of the genes related to ACC deaminase under Cd2+ stress, which was concurrent with the downregulation of genes related to the cell cycles, suggesting a potential protective mechanism against the cytotoxicity induced by Cd2+. These results indicate that strain A23T has a substantial potential for application as a novel and environmentally friendly inoculant to regulate the growth and development of plants in soil contaminated with Cd2+, and it will contribute to an understanding of the relative molecular mechanisms that underlie the response of strain A23T under Cd2+ stress.