Scientists engineer bacteria to extract rare earths

November 23, 2021

A lab-grown crystal of a synthetic form of the rare earth mineral, monazite, shows extensive damage to one face after exposure to bio-leaching compound generated by Gluconobacter oxydans (Courtesy Cornell University)

A study recently published in Nature Communications, ‘Generation of a Gluconobacter oxydans knockout collection for improved extraction of rare earth elements’, has described the use of genetically engineered micro-organisms to process rare earth elements (REE) in a way which is sustainable, efficient and cost effective. The paper was written by Alexa M Schmitz, Brooke Pian, Sean Medin, Matthew C Reid, Mingming Wu, Esteban Gazel and Buz Barstow, researchers at Cornell University, Ithaca, New York, USA.

The demand for REEs is growing, as applications such as wind power generation, electric mobility, and communications technology continue to increase. In the US alone, annual REE needs amount to approximately 10,000 kg, which is extracted from 71.5 million tonnes of raw ore.

Currently, separating the rare earth elements is usually done by dissolving rock with hot sulphuric acid, followed by the use of solvents. The authors of this paper sought to create a micro-organism that does the job succinctly by leveraging the gram-negative bacterium G. oxydans, which produces an acid called biolixiviant which dissolves rock. On its own, the bacterium uses this acid to pull phosphates from rare earth elements; the research team have begun to manipulate the bacterium’s genes so it can extract elements with even more efficiency.

The researchers used ‘Knockout Sudoku’, a technology which allowed them to disable G. oxydans‘ 2,733 genes one by one. This enabled the curation of mutants with specific genes removed, allowing the identification of the specific genes which support the bacterium’s ability to separate elements from rock.

Schmitz identified two such relevant genes: one which accelerates acidification, and one which stops it. This allowed the team to create a mutant which doesn’t regulate its production of biolixiviant, the dissolving acid at the core of the bacterium’s use potential.

In the study, Gazel’s lab at the Department of Earth and Atmospheric Sciences at Cornell helped develop mass spectrometry techniques to measure concentrations of REEs from solutions where mutants were exposed to the ore. According to Gazel, some mutants were seen to gather very high REE concentrations.

Now, the team is working to regulate the gene that accelerates acid production, in an effort to create a system wherein mutated G. oxydans run on cellulose-derived sugars for energy.

“I am incredibly optimistic,” stated Gazel, co-author of the article. “We have a process here that is going to be more efficient than anything that was done before.”

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