Increased biomass and reduced rapeseed Cd accumulation of oilseed rape in the presence of Cd-immobilizing and polyamine-producing bacteria

Two Cd-immobilizing and polyamine-producing bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were characterized for their effects on Cd immobilization, pH, and polyamine production in the solution and the rapeseed biomass and Cd uptake of Brassica napus Qinyou-10 in Cd-contaminated soil. These strains significantly increased pH and reduced water-soluble Cd concentration (25-76%) compared to the controls. Furthermore, strain CL-1 produced more polyamine (71-192%) in the solution than strain X30. Cell surface absorbed Cd content was increased by 23-56% in the presence of strain CL-1 compared to strain X30. The strains significantly increased the rapeseed biomass (12-32%), pH, polyamine content (70-244%), and relative abundance (21-49%) of arginine decarboxylase-producing bacteria (ADPB) of the rhizosphere soils but decreased DTPA-extractable Cd content and rapeseed Cd uptake compared to the controls. Notably, strain CL-1 had higher ability to reduce the rapeseed Cd and DTPA-extractable Cd contents and increase the abundance of ADPB than strain X30. Our results showed the distinct impact of these strains on the rapeseed Cd uptake and available Cd content and suggested that these strains reduced the available Cd and rapeseed Cd uptake by increasing the cell adsorption of Cd, abundance of ADPB, polyamine production, and pH in the rhizosphere soils.