Metal(loid)-resistant bacteria reduce wheat Cd and As uptake in metal(loid)-contaminated soil

This study characterized the effect of the metal(loid)-resistant bacteria Ralstonia eutropha Q2-8 and Exiguobacterium aurantiacum Q3-11 on Cd and As accumulation in wheat grown in Cd- and As-polluted soils (1 mg kg−1 of Cd + 40 mg kg−1 of As and 2 mg kg−1 of Cd + 60 mg kg−1 of As). The influence of strains Q2-8 and Q3-11 on water-soluble Cd and As and NH4+concentration and pH in the soil filtrate were also analyzed. Inoculation with these strains significantly reduced wheat plant Cd (12–32%) and As (9–29%) uptake and available Cd (15–28%) and As (22–38%) contents in rhizosphere soils compared to the controls. Furthermore, these strains significantly increased the relative abundances of the arsM bacterial As metabolism gene and of Fe- and Mn-oxidizing Leptothrix species in rhizosphere soils. Notably, these strains significantly reduced water-soluble Cd and As concentrations and increased pH and NH4+ concentration in the soil filtrate. These results suggest that these strains increased soil pH and the abundance of genes possibly involved in metal(loid) unavailability, resulting in reduced wheat Cd and As accumulation and highlight the possibility of using bacteria for in situ remediation and safe production of wheat or other food crops in metal(loid)-polluted soils.