Abstract
To guarantee the supply of critical elements in the future, the development of new technologies is essential. Siderophores have high potential in the recovery and recycling of valuable metals due to their metal-chelating properties. Using the Chrome azurol S assay, 75 bacterial strains were screened to obtain a high-yield siderophore with the ability to complex valuable critical metal ions. The siderophore production of the four selected strains Nocardioides simplex 3E, Pseudomonas chlororaphis DSM 50083, Variovorax paradoxus EPS, and Rhodococcus erythropolis B7g was optimized, resulting in significantly increased siderophore production of N. simplex and R. erythropolis. Produced siderophore amounts and velocities were highly dependent on the carbon source. The genomes of N. simplex and P. chlororaphis were sequenced. Bioinformatical analyses revealed the occurrence of an achromobactin and a pyoverdine gene cluster in P. chlororaphis, a heterobactin and a requichelin gene cluster in R. erythropolis, and a desferrioxamine gene cluster in N. simplex. Finally, the results of the previous metal-binding screening were validated by a proof-of-concept development for the recovery of metal ions from aqueous solutions utilizing C18 columns functionalized with siderophores. We demonstrated the recovery of the critical metal ions V(III), Ga(III), and In(III) from mixed metal solutions with immobilized siderophores of N. simplex and R. erythropolis.
Highlights
Due to the continuously growing world population and the increasing competition with emerging economies for resources, the industrial nations have to face new challenges in terms of securing their raw materials supply
We report the search for suitable metal-chelating siderophores, which could be applied for the recovery of valuable metals, starting from a screening of over 70 strains for siderophore production as well as metal binding and ending up with siderophore-loaded solid-phase extraction columns in laboratory scale
Some of the strains used for the siderophore screening were retrieved from the German strain collection (DSMZ); others were retrieved from the strain collection of the Institute of Bioscience in Freiberg
Summary
Due to the continuously growing world population and the increasing competition with emerging economies for resources, the industrial nations have to face new challenges in terms of securing their raw materials supply. The supply of valuable metals is significantly dependent on their occurrence, existing resources, given processing methods, and recycling possibilities. The development of new processes that allow metal extraction from low concentrated solutions or recycling material is gaining in importance [1]. Siderophores and other natural chelators possess promising metal-binding characteristics that provide a high potential for utilization in metal extraction processes and treatment of metal-loaded waters. These low molecular weight compounds have been reported to complex different kinds of metals including valuable metals (e.g., rare earth elements (REE), actinides, Ga, In, V, Co, noble metals) and contaminating metals (e.g., Pd, Ni, Cd, U) [3,4].
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