Metal-Eating Bacteria That Chomps On Nails Could Make Mining More Environmentally Friendly

Metal-eating bacteria live in extreme environments, so it's not surprising some were found in the world's highest-altitude geyser field in the Atacama Desert. A species found here could help clean up mine sites and make copper extraction more environmentally friendly. Image credit: rainagaoka/Shutterstock.com  

If you are what you eat then Leptospirillum is seriously metal. Leptospiriium is a genus of microorganisms that feed on certain metals, in their case iron, at least when they can't get any of their preferred foods. Chilean scientist Nadac Reales is working on using this capacity to clean up former mine sites, and has manipulated her microbial agents to the point they will consume a nail in three days. Other scientists are also using biological agents for mining, but targeting more exotic metals.

Chile is the largest copper producer in the world. Many low-carbon technologies, such as electric cars, require more copper than those they replace, so demand is likely to grow. According to a profile by AFP, Reales was working on the use of microbes to improve copper extraction when she realized they might serve better by cleaning up the pollution mining operations leave behind.

"I realized there were various needs in the mining industry, for example what happened with the metallic waste," Reales told AFP.

Nadac Reales with flasks containing metals and microbes that eat them. Image Credit: Rudanac Biotec

Gaining energy by oxidizing metals is harder than getting it from sunlight, or eating something that does, so organisms that make a lifestyle out of it usually live in conditions far from the norm, earning the name extremophiles.

Reales went searching in places hostile to most life for organisms that would suit her needs. At the Tatio geysers in the Atacama desert, in the world's highest-altitude geyser field in possibly the world's harshest desert, she found Leptospirillum that thrive in acidic environments and can tolerate high concentrations of metal. Reales tested their capacity to break down metal objects, telling AFP that “At first the bacteria took two months to disintegrate a nail.” However, she found that if deprived of other food sources the Leptospirillum got hungry enough to focus on the task.

Over two years of selecting the most suitable strains, and adjusting the conditions in which she kept them, Reales was able to get the nail-consuming time down to three days.

Reales established Rudanac Biotec to exploit this capacity, and is seeking money to scale up the operations to see how long it takes to tackle 50 tons of rock.

Leptospirillum pose no threat to humans, nor to healthy environments, and Reales claims their capacity goes beyond remediation. The reddish liquid left behind after all the iron has been eaten can be used to improve the recovery of copper, replacing existing toxic leaching chemicals.

Eating a nail is one thing, but Reales will know her work is ready for prime time when it can consume the ore that fills one on the hoppers behind her. Image Credit: Rudonac Biotec

Reales is just one among many researchers seeking to find ways to use biological processes for metal extraction. Dr Josepch Cotruvo of Penn State University is part of a team that has demonstrated you don't always need the bacteria themselves to do the job. In ACS Central Science, Cotruvo and co-authors have demonstrated the use of Ianmodulin, a protein isolated from bacteria, for metal extraction, either in mines or in electronics recycling.

Lanmodulin binds to rare Earth metals, which are used in mobile phones, electric vehicles, and many wind turbines. Although rare Earths are not as uncommon as their name suggests, they are hard to extract in environmentally friendly ways, and refineries that could break a Chinese near-monopoly on their production have been resisted because of the damage feared from processing, rather than the mining themselves. Lanmodulin could resolve that dilemma.

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