Resumen
- Phytoremediation can be assisted by microorganisms, which promote plant growth and increase heavy metal availability in soil. In this study, we aimed at evaluating the effect of two plant growth-promoting bacteria (PGPB) on phytoextraction of copper (Cu) by maize. We chose the strains based on their ability to synthesize indole compounds, produce siderophores, solubilize phosphorus, and increase soil conductivity and extractable Cu in soil. Then, in glasshouse experiments, we assessed their ability to increase biomass, chlorophyll content, and Cu extraction by maize. Results showed that Acinetobacter sp. RG30 and Pseudomonas putidaGN04 were overall the most active strains to synthesize indole, produce siderophores, and solubilize phosphorus, and hence selected for further studies. Also, both were able to significantly increase soil conductivity and release Cu from soil compared to control. Glasshouse experiments showed that Cu had a negative effect on plant growth, but inoculation with bacteria promoted plant growth and chlorophyll content in its presence (p < 0.05). Notably, the effect of inoculation on plant growth was larger on contaminated than on uncontaminated soil, which suggests an overall bacterial effect for alleviation of stress caused by Cu. Inoculation with RG30 or GN04 improved Cu extraction by maize (p < 0.05); interestingly, co-inoculation led to the highest accumulation (200 μg Cu/g plant dry weight). We conclude, therefore, that inoculation with RG30 and GN04 improves metal extraction by increasing plant growth, fitness, and availability of minerals in soil, which represents an important tool for the improvement of phytoextraction processes in polluted environments.