Metal-tolerant Enterobacter sp strain EG16 enhanced phytoremediation using Hibiscus cannabinus via siderophore-mediated plant growth promotion under metal contamination

This study is aimed to investigate the efficiency of plant growth-promoting (PGP) strategies of Enterobacter sp. strain EG16 under metal stress and its potential application in phytoremediation. Production of siderophores and indole-3-acetic acid (IAA) by EG16 were assessed in a hydroponic system in which Hibiscus cannabinus was grown with different concentrations of Cd and Fe. A pot experiment was also carried out to evaluate the practical effect of EG16 on H. cannabinus growth and remediation efficiency. Inoculation with EG16 significantly improved plant growth, probably as a result of increased plant uptake of Fe and immobilization of Cd2+, which resulted in decreased plant accumulation of Cd. Increased production of siderophores by EG16 in response to Cd exposure appeared to be the PGP strategy functioning in the EG16-H. cannabinus association. The bacterial Cd response system promoted plant and bacterial uptake of Fe, alleviated Cd-induced inhibition of bacterial IAA production, and potentially assisted in metal immobilization in the rhizosphere. The EG16-H. cannabinus association may be useful for phytostabilization, as it exhibits good plant growth, low plant accumulation of metals, and reduced metal bioavailability in soil.