A published in Nature Communications describes a proof of principle for engineering a bacterium, Gluconobacter oxydans, that takes a first step towards meeting skyrocketing rare聽earth聽element demand in a way that matches the cost and efficiency of traditional thermochemical extraction and refinement methods and is clean enough to meet US environmental standards.
鈥淲e鈥檙e trying to come up with an environmentally friendly, low-temperature, low-pressure method for getting聽rare earth elements聽out of a rock,鈥� Buz Barstow, the paper鈥檚 senior author and an assistant professor at Cornell University, said in a media statement.
To meet US annual needs for rare earth elements, roughly 71.5 million tonnes of raw ore would be required to extract 10,000 kilograms of elements.
Current methods rely on dissolving rock with hot sulphuric acid, followed by using organic solvents to separate very similar individual elements from each other in a solution.
鈥淲e want to figure out a way to make a bug that does that job better,鈥� Barstow said.
G. oxydans is known for making an acid called biolixiviant that dissolves rock; the bacteria uses the acid to pull phosphates from rare earth elements. Thus, Barstow and his team have begun to manipulate G. oxydans鈥� genes so it extracts the elements more efficiently.
To do so, the researchers used a technology called Knockout Sudoku, that allowed them to disable the 2,733 genes in G. oxydans鈥� genome one by one. The team curated mutants, each with a specific gene knocked out, so they could identify which genes play roles in getting elements out of rock.
Lead author Alexa Schmitz, then identified genes involved in two systems in G. oxydans; one that puts the brakes on acidification and another that accelerates it.
鈥淲e believe that this mutant can鈥檛 tell when it鈥檚 had enough phosphate, so it keeps producing acidic biolixiviant to dissolve more,鈥� Schmitz said.
The team is also working to find ways to regulate the gene that accelerates acid production. They hope to create a system where bacteria run on cheap cellulose-derived sugars for energy.
鈥淚 am incredibly optimistic,鈥� Esteban Gazel, co-author of the article and associate professor of earth and atmospheric sciences, said. 鈥淲e have a process here that is going to be more efficient than anything that was done before.鈥�
In the study, Gazel鈥檚 lab helped develop mass spectrometry techniques, which Schmitz used to measure concentrations of rare earth elements from solutions where mutants were exposed to ore. 鈥淔or some of the mutants, they were able to get very high concentrations [of rare earth elements from ore],鈥� Gazel said.