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REE part collection

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Part collection

Our project focused on developing a selective Rare Earth Elements (REE) capturing system which potentially allows for their targeted recovery from liquid wastestreams. By exploiting the natural ability of some bacteria to leach REE from ores, we developed a dual-module protein system that incorporates specific REE-binding proteins bound to curli fiber, aiming to maximise the REE capturing potential and offering a greener process for lanthanides extraction from e-waste sludge.

Methylotrophic bacteria such as Methylorubrum extorquens AM1 - amongst others - use selective lanthanides-binding proteins, including lanmodulins, to intake REE and use them as co-factors for several important metabolic reactions (Wang et al., 2020). Moreover, recent advances in protein engineering yielded binding proteins that are highly selective for specific lanthanides, such as GLAM - selective for gadolinium. Our system exploits the polymeric features of the CsgA subunits of curli fibers, which allowed us to design an REE-capturing system that relies on the interaction between a DogTag and a DogCatcher (Keeble et al., 2022). We engineered each CsgA subunit of the curli fiber to display a DogTag (BBa_25BU4MXM) and each REE-binding protein to be fused with a DogCatcher, so that upon close proximity, each CsgA subunit of the curli can bind to one specific binding protein, maximising the metal-ions' binding to the protein system.

Both empirical and bioinformatic modeling data retrieved the stability of the REE-ion / curli+REE-binding protein system, highlighting the promising possibility to eventually scale up this system and incorporate it in existing e-waste recycling wastestreams.

The binding proteins of our lanthanide-selective capturing system enable the targeted recovery of five different REE: Lanthanum and Cerium (La&Ce, BBa_25K7UGOJ), Dysprosium (Dy, BBa_25WS2YVO), Neodymium (Nd, BBa_25IUKDSB), and Gadolinium (Gd, BBa_25ODY87T). Additionally, there is potential to apply the same principle for Praseodymium binding protein (Pr, BBa_25L0PQDR), thus allowing the recovery of the Pr-binding protein cloning process and experimental validation of its functioning needs to be carried out before confirming such potential - a possible point of exploration for future iGEM teams.

All parts of the collection are listed in the table below, and fully characterised with their respective experimental data on the iGEM REE part collection repository.

Table 1: Schematic representation of the binding protein and curli gene modules. The table lists the collection of binding proteins employed in our REE-binding system, with the respective PDB identifier. A schematic representation of the gene for our curli-DogTag module is also displayed in the last row. All REE-binding protein genes are preceded by a T-7 promoter and an IPTG-inducible Lac operator, as well as a ribosome binding site (not shown).
Protein Metal (Target Metal) Graphical DNA representation Link iGEM parts Original Publications
Lanmodulin 8DQ2 (La/Ce) 8DQ2 BBa_25K7UGOJ. Mattocks et al. (2023)
Lanmodulin 8FNR (Dy) 8FNR BBa_25WS2YVO. Mattocks et al. (2023)
GLamouR GLAM (Gd) GLAM BBa_25ODY87T. Lee et al. (2025)
Lanmodulin 8FNS (Nd) 8FNS BBa_25IUKDSB. Harris & Wesley, (1986)
Pr (PedH 6ZCW) 6ZCW BBa_25L0PQDR. Wehrmann et al. (2020)
CsgA-Tag (curli-DogTag) CsgA BBa_25BU4MXM. Tay et al., (2018)

View Table PDF

All REE-binding protein parts are under the control of an IPTG-inducible Lac operator, and yield optimal protein production under 1mM Isopropyl-β-D-1-thiogalactopyranoside.

The development of this part collection shows great potential for targeted recovery of lanthanides from industrial e-waste sludge treated after precious metal extraction, supporting the circular extraction and reintegration of rare earth elements (REE) into the electronics manufacturing industry from secondary sources.

Overall, our project’s part collection aims at solving pressing environmental concerns and hopes to bring about sustainable innovation in the e-waste recycling sector. Moreover, such contribution lays the blueprint for novel REE-binding protein design for selective recovery and targeted separation of lanthanides - one of the most challenging aspects of metal recovery from e-waste.

Other research teams are encouraged to freely use our designed part collection to advance understanding in these areas. By building on the foundation we have established, we hope that they can further characterize and optimize REE extraction and recovery.

References