Genetic Modification of Acidithiobacillus ferrooxidans for Rare-Earth Element Recovery under Acidic Conditions

Area of Science:

• Biotechnology and Bioengineering
• Environmental Science and Engineering
• Materials Science and Engineering

Background:

• Growing global demand for rare-earth elements (REEs) necessitates sustainable recovery methods.
• Calcium-binding domains, like EF hands and RTX domains, can bind lanthanides due to similar ionic properties.
• Lanmodulin protein exhibits high affinity for lanthanides over calcium, and *Acidithiobacillus ferrooxidans* is suitable for bioleaching.

Purpose of the Study:

• To engineer *Acidithiobacillus ferrooxidans* for enhanced biological recovery of REEs.
• To investigate the efficacy of intracellular lanmodulin and periplasmic RTX domains for lanthanide binding.
• To assess the potential of engineered strains for REE reclamation and recycling.

Main Methods:

• Recombinant intracellular expression of lanmodulin in *A. ferrooxidans*.
• Periplasmic expression of an RTX domain fused to rusticyanin in *A. ferrooxidans*.
• Quantification of lanthanide binding affinity and selectivity in pure and mixed metal solutions.

Main Results:

• Lanthanide binding improved up to 4-fold with lanmodulin and 13-fold with RTX domains.
• Lanthanide presence in growth media enhanced protein expression, potentially via improved protein stability.
• Engineered strains showed higher recovery and selectivity for REEs (Tb³⁺, Pr³⁺, Nd³⁺, La³⁺) over non-REEs (Fe²⁺, Co²⁺).

Conclusions:

• Engineered *A. ferrooxidans* strains expressing lanmodulin or RTX domains demonstrate significant potential for REE bio-recovery.
• The developed bio-reclamation strategy offers a promising avenue for sustainable REE recycling.
• Further research into optimizing these microbial systems could enhance REE reclamation efficiency.