NIEHS grantees from the University of Pennsylvania’s (Penn) Department of Earth and Environmental Sciences recently discovered that bacteria from extreme marine environments have the ability to detoxify asbestos. Their study, published in Journal Applied and Environmental Microbiologysuggests that marine microbes may be better candidates for asbestos bioremediation than previously tested fungi and soil bacteria.

Asbestos materials, a group of naturally occurring minerals that were once widely used in a range of industries for their strength and heat resistance, are notorious for being a health hazard. Although their use has declined significantly, the minerals are not banned in the United States, and people may still be exposed to them when asbestos-containing buildings are disturbed during renovation or demolition.

Ileana Perez-Rodriguez, Ph.D., and Reto Gierre, Ph.D.
Senior author Perez-Rodriguez, right, together with Geire, left, studied the ability of two bacterial species, D. palaeocoriens and T. ammonificans, to detoxify asbestos. (Photos courtesy of Reto Giere and Brooke Sittinson)

The threat hit close to home for the researchers when several schools in the Philadelphia school district were closed after failing asbestos inspections. Penn has pledged to contribute $100 million to the school district – $10 million annually for 10 years – that will be used to address environmental hazards including asbestos and lead in public school buildings. However, better treatment options are needed to deal with asbestos.

“We wanted to expand asbestos bioremediation research by exploring ways to reduce the toxicity of these minerals for safe disposal or reuse as secondary raw materials,” said the senior author. Ileana Perez-Rodriguez, Ph.D.An assistant professor of earth and environmental sciences who specializes in studying extremophilic deep-sea microbes.

Bacteria use iron present in asbestos to grow

teamed up with Perez-Rodriguez Reto Gere, Ph.D., which have a long history characterizing asbestos minerals. They thought these extremophilic microbes might be good candidates for asbestos bioremediation because they use up inorganic compounds and interact with a variety of minerals in their natural environment.

The team focused on two bacterial species, Deferisoma palaeocorians and Thermovibrio ammonificans, to target two aspects of asbestos minerals that make them dangerous when inhaled: their iron content, which is largely responsible for the material’s carcinogenic effects. Is, and their fibrous structure, which causes inflammation. ,

Minerals used in the study, from left to right: chrysotile, crocidolite, and tremolytic actinolite
Minerals used in the study, from left to right: chrysotile, crocidolite, and tremolitic actinolite. (Images courtesy of Ruggero Vigliaturo)

To test the microbes’ ability to detoxify asbestos, the researchers placed them in small bottles filled with liquid, which also contained asbestos minerals, at 60 °C or 75 °C – the microbes’ preferred temperatures – for seven days. During this period, the researchers took samples of the liquid media to track changes in cell growth and chemical composition, and they used electron microscopy to look for changes in mineral composition.

They found that D. palaeocorynes, which uses iron as part of its metabolism, can effectively remove some of the iron from asbestos when used to grow it. However, the removal of iron did not alter the overall fibrous structure of the mineral, which is partly responsible for its toxicity.

“It’s a gradual process of taking a highly dangerous mineral and making it less dangerous,” Perez-Rodriguez said. “You can make the mineral less toxic by eliminating the chemical reaction that comes with the iron, but you still have that fibrous structure, so the next question is: ‘How do we break down the shape?'”

Bacteria can target the fibrous structure

Asbestos minerals are composed of a silicate backbone, and previous studies have shown that removal of silicon and magnesium ions from this backbone can disrupt its fibrous structure. That’s where another bacteria, T. ammonificans, came in.

Experimental titanium foil surfaces provided to the deep-sea vent bacterium T. ammonificans while growing in the presence of chrysotile asbestos for seven days
Tubular structures resembling “little vent chimneys” were observed in experimental titanium foil surfaces provided to the deep-sea vent bacterium T. ammonificans while grown in the presence of chrysotile asbestos for seven days. (Images courtesy of Jessica Choi)

“We can see through microscopy that these microorganisms incorporate silicon into their biofilms,” said Pérez-Rodriguez. “Normally when we think of biofilms, we think of a kind of sticky goo, but, in this case, biofilms are actually quite rigid – they’re basically little houses made of rocks.” Are.”

The researchers found that T. ammonificans can accumulate silicon from “serpentine” asbestos, which has curly fibers, but not from “amphibole” asbestos, which has straight needle-shaped fibers.

“This really highlights the difficulty of approaching asbestos remediation as a one-size-fits-all solution, given the unique chemical structures and crystal structures associated with each asbestos mineral,” Perez-Rodriguez explained.

future directions

Microbial-based asbestos remediation is a desirable alternative to current asbestos remediation methods, which involve either heating it to very high temperatures and pressures or treating it with strong acids or alkalis. However, more research is needed to test how well these methods can be used to remediate asbestos on a large scale.

“This was just the first lab test, and of course there are still questions, and we have to do more research, but hopefully we can take this to the next level,” Gere said.

The study was co-authored by former postdoctoral researcher Jessica Choi, PhD, who is now a postdoctoral researcher at the University of Michigan, and Ruggero Vigliaturo, PhD, now an assistant professor at the University of Turin.

Citation: Choi JK, Vigliaturo R, Gierre R, Pérez-Rodriguez I. Microbe-mineral interactions between asbestos and thermophilic chemolithoautotrophic anaerobes., Appl Environ Microbiol 89(6):e0204822.

(This article is adapted from the publication of July 6 pen todayLiana F. Waite, Science News Officer.)

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