Endophytic bacteria-assisted cadmium removal in sunflower stalks: towards safe biomass recycling

Cadmium (Cd) contamination in agricultural soils is one of the major threats to food safety and environmental health. In a phytoremediation program for the extraction of Cd by plants, one critical challenge is the management of harvested biomass because of its highly contaminant content. This study investigates the use of endophytic bacteria to assist in Cd removal from sunflower stalks, aiming to make the biomass safer for reuse as fertilizer. Sixteen endophyte strains were isolated from sunflower plants grown in Cd-contaminated soils, out of which two strains, J14 and J15, namely Enterobacter roggenkampii and Kosakonia cowanii, respectively, showed the most potential for Cd removal. Under the optimized conditions, 42.03% and 37.99% Cd removal efficiency could be achieved by J14 and J15, respectively. More than 50% of some specific forms of Cd (F2, F4, F5) in sunflower stalks can be reduced during extraction. Importantly, the treatment with endophytes lowered Cd in contaminated biomass without significant reductions in the major plant nutrients (nitrogen, phosphorus, and potassium), thus rendering it safe for its reuse as fertilizer. This study offers a novel perspective on biomass contamination in phytoremediation, suggesting a new environmentally friendly approach for the recycling of polluted plant material towards safer and more economic phytoremediation practices.