Metal tolerance of rhizobial strains isolated from nodules of herbaceous legumes (Medicago spp. and Trifolium spp.) growing in mercury-contaminated soils

► We isolated 59 rhizobial strains from herbaceous legumes growing in Hg-polluted soils. ► Several strains exhibited extremely high tolerance to Hg. ► Strains displaying multiple metal tolerances were also identified. ► Positive and negative correlations were found between metal tolerance responses. ► Tolerant strains may be potentially useful to develop Hg bioremediation technologies.