Root nodule bacteria isolated from Lotus uliginosus for future use in phytostabilization of arsenic contaminated soils

In recent decades there has been growing concern around heavy metals and metalloid contamination in soil. Arsenic (As) is a ubiquitous trace metalloid. The high levels of this metalloid in soils are a consequence of human activities and also from natural inputs. In general, the biodiversity of microorganisms and plants decreases drastically in contaminated soils. The knowledge that some leguminous plants, mainly certain species of Lotus, are growing well in such soils has attracted our attention for studying symbioses that are well adapted to harsh conditions. In this work we studied the rhizobial population existing in the root nodules of native Lotus uliginosus Sch. growing in a central region of Portugal. This legume grows in soils particularly affected by As due the discharge of industrial liquid effluents from fertilizer and chemical facilities. Diversity and tolerance to different concentrations of As of root nodule bacteria were studied. Our results showed that the symbioses between L. uliginosus and As tolerant Bradyrhizobium isolates were efficient when a nutrient medium containing high As concentrations was used. The present work highlights the capacity of L. uliginosus to grow and establish nitrogen-fixing symbioses in soils strongly contaminated with As and its potential for future use to promote vegetation cover to stabilize As contaminated soils.