Lupinus albus plants acquire mercury tolerance when inoculated with an Hg-resistant Bradyrhizobium strain

One strain of Bradyrhizobium canariense (L-7AH) was selected for its metal-resistance and ability to nodulate white lupin (Lupinus albus L.) plants, from a collection of rhizobial strains previously created from soils of the Almadén mining district (Spain) with varying levels of Hg contamination. Plants were inoculated with either strain L-7AH (Hg-tolerant) or L-3 (Hg-sensitive, used as control), and watered with nutrient solutions supplemented with various concentrations (0-200μM) of HgCl2 in a growth chamber. L.albus inoculated with L-7AH were able to nodulate even at the highest concentration of Hg while those inoculated with L-3 had virtually no nodules at Hg concentrations above 25μM. Plants inoculated with L-7AH, but not those with the control strain, were able to accumulate large amounts of Hg in their roots and nodules. Nodulation with L-7AH allowed plants to maintain constant levels of both chlorophylls and carotenoids in their leaves and a high photosynthetic efficiency, whereas in those inoculated with L-3 both pigment content and photosynthetic efficiency decreased significantly as Hg concentration increased. Nitrogenase activity of plants nodulated with L-7AH remained fairly constant at all concentrations of Hg used. Results suggest that this symbiotic pair may be used for rhizoremediation of Hg-contaminated soils

Mercury accumulation in legume plants inoculated with rhizobia isolated from mercury-contaminated areas

Trabajo presentado en la XIII Reunión Nacional de la Sociedad Española de Fijación de Nitrógeno, celebrada en Zaragoza (España), del 15 al 18 de junio de 201

Selección de cepas de rhizobia tolerantes a mercurio por su capacidad de bioacumulación y su efectividad en leguminosas arbustivas

Trabajo presentado en el II Iberoamerican Conference on Benefical Interactions Microorganism-Plant-Environment (IBEMPA), celebrado en Sevilla (España), del 2 al 6 de septiembre de 201

La inoculación con rizobios tolerantes a mercurio tiene un efecto positivo sobre plantas de lupino cultivadas en sustratos contaminados con dicho metal

Trabajo presentado en la XIX Reunión de la Sociedad Española de Fisiología Vegetal - XII Congreso Hispano-Luso de Fisiología Vegetal, celebrada en Castelló de la Plana, Valencia (España), del 21 al 24 de junio de 201

Isolation and characterization of rhizobia from legumes grown in soils with high mercury contamination and inoculation with selected Hg-tolerant strains

Trabajo presentado en el 10th International Conference on Mercury as a Global Pollutant (ICMGP), celebrado en Halifax, Nova Scotia (Canadá), del 24 al 29 de junio de 201

Inoculation with Hg-resistant rhizobia enhances Hg tolerance and phytoremediation capacity of legumes

Trabajo presentado en el Energy and Environment Knowledge Week 2014 (E2KW2014), celebrado en Toledo (España), del 30 al 31 de octubre de 201

Selected mercury-tolerant rhizobia facilitate phytoremediation capability of shrub legumes

Trabajo presentado en el 11th European Nitrogen Fixation Conference (ENFC2014), celebrado en Tenerife (España), del 7 al 10 de septiembre de 2014The Rhizobium-legume symbiosis is being tested as an alternative tool for phytoremediation of Hg-contaminated soils in Almadén (Ciudad Real, Spain). Previously, rhizobia from these soils were isolated and characterized to obtain a collection of rhizobia, adapted to the soil characteristics of the Almadén Mining District, that could be used as inoculants of legumes for phytoremediation purposes (1). The two main objectives of the present work were to continue analyzing the diversity of rhizobia from different areas of Almadén and to evaluate the phytoremediation and revegetation capacity of shrub legumes inoculated with the previously-selected Hg-tolerant strains, first in greenhouse and then in field experiments. 16S rRNA gene sequencing was used for the species affiliation of 14 strains of rhizobia isolated from 7 species of legumes belonging to the genera Medicago, Trifolium, Vicia, Lupinus, Retama, Phaseolus and Colutea. The greenhouse experiment consisted on the inoculation of four shrub legumes (Adenocarpus hispanicus, Spartium junceum, Retama monosperma and Cytisus striatus) with selected rhizobial strains. The plants were grown in pots, with vermiculite as a substrate, under controlled conditions. Control plants were watered with Hg-free nutrient solution while the rest were watered with Hg-containing nutrient solution. The results showed that, for most legume-rhizobium pairs, Hg negatively affected different traits such as aerial part and root weights, number and weight of nodules or nitrogenase activity. However, Retama plants inoculated with either of two Hg-tolerant strains of Rhizobium radiobacter and Bradyrhizobium canariense, were able to maintain similar values of the above-mentioned traits in the absence as well as the presence of Hg. Mercury accumulation was very high in nodules and roots, but not in leaves, suggesting that phytoremediation of Hg-contaminated soils using legumes inoculated with Hg-tolerant rhizobia may be achieved through rhizostabilization. The field experiment consisted of two plantations of shrub legumes inoculated with selected Hg-tolerant rhizobia (the same as in the greenhouse experiment) established in two areas which soils had different levels of Hg contamination. The results showed that the survival and accumulation capacity of the plants varied depending on the legume species and the inoculated strain. A high number of gaps were detected, although a higher persistence of legumes inoculated with the more Hg-tolerant strain was observed. Monitoring of the nodulation occupancy (analysis of the 16S-23S rRNA intergenic spacers (IGS)) has confirmed the presence of the inoculated strains in nodules of Cytisus and Spartium in the Almadén soils.This work was supported by JJ.CC. Castilla - La Mancha (POII10-0211-5015), Ministry of Science and Innovation (AGL2009-10371) and Comunidad de Madrid (S2009/AMB-1511)

Phytoremediation capability of shrub legumes inoculated with Hg-tolerant selected rhizobia

Trabajo presentado en el International Congress of Phytoremediation of Polluted Soils, celebrado en Vigo (España), del 29 al 30 de julio de 201

Genetic and phenotypic characterization of rhizobia from legumes grown in soils with high mercury contamination

Trabajo presentado en la XIII Reunión Nacional de la Sociedad Española de Fijación de Nitrógeno, celebrada en Zaragoza (España), del 15 al 18 de junio de 201

Caracterización fenotípica y genética de rhizobia de leguminosas crecidas en suelos con altas concentraciones de mercurio

Trabajo presentado en la II Reunión Programa Microambiente de la Comunidad de Madrid, celebrada en Madrid (España), del 30 de septiembre al 1 de octubre de 201