Prospecting metal-resistant plant-growth promoting rhizobacteria for rhizoremediation of metal contaminated estuaries using Spartina densiflora.

In the salt marshes of the joint estuary of Tinto and Odiel rivers (SW Spain), one of the most polluted areas by heavy metals in the world, Spartina densiflora grows on sediments with high concentrations of heavy metals. Furthermore, this species has shown to be useful for phytoremediation. The total bacterial population of the rhizosphere of S. densiflora grown in two estuaries with different levels of metal contamination was analyzed by PCR denaturing gradient gel electrophoresis. Results suggested that soil contamination influences bacterial population in a greater extent than the presence of the plant. Twenty-two different cultivable bacterial strains were isolated from the rhizosphere of S. densiflora grown in the Tinto river estuary. Seventy percent of the strains showed one or more plant growth-promoting (PGP) properties, including phosphate solubilization and siderophores or indolacetic acid production, besides a high resistance towards Cu. A bacterial consortium with PGP properties and very high multiresistance to heavy metals, composed by Aeromonas aquariorum SDT13, Pseudomonas composti SDT3, and Bacillus sp. SDT14, was selected for further experiments. This consortium was able to two-fold increase seed germination and to protect seeds against fungal contamination, suggesting that it could facilitate the establishment of the plant in polluted estuaries.