Cadmium tolerance, Phytoremediation, Enterobacter hormaechei X20, Perennial ryegrass, Plant growth-promoting rhizobacteria (PGPR), Ion homeostasis, Environmental pollution, TD172-193.5, Environmental sciences, GE1-350

Cadmium (Cd) contamination in soils poses a critical environmental challenge, jeopardizing both agricultural productivity and food safety. The utilization of plant growth-promoting rhizobacteria (PGPR) emerges as a promising strategy for mitigating the adverse effects of heavy metal stress on plant health and development. This study investigates the effectiveness of Enterobacter hormaechei X20 in enhancing Cd tolerance in perennial ryegrass, a species renowned for its phytoremediation potential. Strain X20 demonstrated multiple PGPR traits, including phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore secretion. Under Cd stress, X20 significantly stimulated plant growth, elevated canopy height, and preserved leaf water content. Additionally, X20 inoculation enhanced Cd uptake and reestablished ion homeostasis by augmenting Fe2+, Cu2+, Zn2+, and Mn2+ levels. It also improved photosynthetic efficiency, particularly by optimizing PSII activity, and strengthened antioxidant defense, alleviating oxidative stress. Metabolomic analysis revealed significant modulations in amino acid and sugar metabolism, marked by increased in serine and glycine levels under Cd stress. Furthermore, fructose and glucose levels rose, while sucrose levels declined, reflecting metabolic reprogramming that facilitates stress adaptation. These findings suggest that Enterobacter hormaechei X20 holds great promise as a bioinoculant for enhancing phytoremediation efficiency and plant resilience in Cd-contaminated soils, providing a sustainable strategy for managing heavy metal pollution in agriculture.