DL-alanine promotes the colonization of Pseudomonas aeruginosa and their synergistic enrichment of selenium and decrease of cadmium absorption by Brassica napus

In selenium-rich regions, selenium and cadmium coexist in soil, posing a threat to agricultural product safety. This study explores the influence of Pseudomonas aeruginosa and DL-alanine on selenium and cadmium uptake in Brassica napus. Through pot and medium experiments, along with FTIR and XPS analyses, we found that DL-alanine significantly boosts Pseudomonas aeruginosa biofilm formation and root colonization. Compared with the control group, the combined treatment of DL-alanine and Pseudomonas aeruginosa increased the selenium content in the shoots by 55.8 %, and decreased the cadmium content in the shoots and roots by 66.3 % and 67.9 %, respectively. The direct reason for this result is that the available selenium in the rhizosphere soil increased by 32 % and the available cadmium decreased by 10 %. Further investigation shows that DL-alanine promotes the transformation of Se(0) to Se(-II) and the formation of CdSe nanoparticles by Pseudomonas aeruginosa, which enhances the availability of selenium and reduces that of cadmium. Furthermore, gene expression analysis revealed that the expression levels of selenium-related genes were upregulated, while those of cadmium transport genes were downregulated. This study proposes a new method for improving selenium utilization and reducing cadmium absorption in soils where selenium and cadmium coexist, providing a theoretical basis for safer agricultural practices.