Soil fungi reduce the iron content and the DNA damaging effects of asbestos fibers

Our plain-English summary of Soil fungi reduce the iron content and the DNA damaging effects of asbestos fibers, by S. Daghino, F. Turci, M. Tomatis, et al (Environmental Science & Technology, 2006).

The study

• Authors: S. Daghino, F. Turci, M. Tomatis, A. Favier, S. Perotto, T. Douki, B. Fubini
• Journal: Environmental Science & Technology
• Published: 2006;40(18):5793-8
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Some soil fungi growing on asbestos fibers release chelators and antioxidants. The bioweathering potential of fungi has thus been envisaged as a possible route for bioremediation of asbestos rich soils, where no inactivation procedures have been established so far. The present study reports fungal-mediated modification of the surface reactivity of the fibers and of their potential to damage DNA in vitro. Verticillium sp. and Paecilomyces sp. were selected among the fungi isolated from fragments of chrysotile bearing rocks, as the most potent in iron extraction, and studied in parallel with F. oxysporum, previously reported to modify the surface reactivity of asbestos fibers. One sample of chrysotile from the Western Alps and a sample of UICC (Union Internationale Contre le Cancer) crocidolite were incubated with or without fungi. All fungi extracted iron from both fibers (7.3% from crocidolite and 33.6% from chrysotile by Verticillium sp.), releasing it into the medium. F. oxysporum and Paecilomyces sp. suppressed the potential of the fibers to release hydroxyl radical, while Verticillium sp. suppressed it on crocidolite but enhanced it on chrysotile, a hallmark of ongoing mobilization of reactive iron. Fibers incubated in the growth medium, but in the absence of fungi, exhibited a remarkable potential to damage DNA in vitro, measured by the generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, while all the fungi reduced such effect. Fungi may thus be regarded as appropriate candidates for bioremediation of asbestos rich soils whereby the reactive iron ions responsible for DNA damage are progressively removed from the fibers.

In plain English

This was a laboratory experiment using asbestos fibers and isolated DNA. The authors placed chrysotile from the closed Balangero asbestos mine near Turin, Italy, and a standard UICC crocidolite sample in dialysis bags in a fungal growth medium for 20 days, with or without one of three soil fungi. Two of the fungi, Verticillium sp. and Paecilomyces sp., came from the Balangero mine soil. The third was Fusarium oxysporum. All three fungi extracted iron from both fibers. From chrysotile they removed 9.7% (F. oxysporum), 33.6% (Verticillium sp.) and 16.7% (Paecilomyces sp.) of the total iron. All three fungi suppressed hydroxyl radical release from crocidolite. For chrysotile, Paecilomyces sp. and F. oxysporum suppressed it, but Verticillium sp. did not change it or even increased it. In a test-tube DNA damage test run with added EDTA and hydrogen peroxide, fibers kept in medium without fungi caused more oxidative DNA damage than untreated fibers. Fibers treated with any of the fungi caused significantly less damage. The authors concluded that fungal weathering may be considered a possible strategy for remediating asbestos-rich soil.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) experiment. Asbestos fibers were incubated with or without soil fungi, then tested for iron loss, surface iron, free radical release, and oxidative damage to isolated (naked) calf thymus DNA.
• Who was studied: No human or animal subjects. Two fungal strains (Verticillium sp. and Paecilomyces sp.) were isolated from the soil of the disused Balangero asbestos mine (Turin, Italy). They were tested together with Fusarium oxysporum, which came from a cultivated soil.
• Exposure: Chrysotile fibers from the Balangero mine (Western Alps) and UICC reference crocidolite fibers. Each was incubated for 20 days with or without one of the three fungi.
• Main results:
  • All three fungi extracted iron from both chrysotile and crocidolite. Verticillium sp. was the most active on both fibers.
  • For chrysotile, the iron extracted was 9.7% (F. oxysporum), 33.6% (Verticillium sp.) and 16.7% (Paecilomyces sp.) of the total iron in the fibers.
  • Verticillium sp. extracted 7.3% of the iron from crocidolite. This figure appears only in the article's abstract.
  • After fungal treatment, the surface of the crocidolite fibers had much less iron than the control fibers kept in medium without fungi. The authors state this effect was mostly limited to the surface.
  • Chrysotile: treatment with Paecilomyces sp. and F. oxysporum blunted hydroxyl radical release.
  • Chrysotile: treatment with Verticillium sp. did not change the fibers' radical release, or even increased it, despite the large amount of iron removed.
  • Crocidolite: all three fungi inhibited the fibers' Fenton (hydroxyl radical) activity.
  • DNA oxidation is given as 8-oxodGuo per 10,000 DNA bases. Background with no fibers was 1.04 (plus or minus 0.09). Untreated crocidolite gave 11.95 (plus or minus 0.30). Crocidolite kept in medium without fungi (control) gave 33.37 (plus or minus 5.12).
  • Untreated chrysotile gave 9.12 (plus or minus 2.35) per 10,000 bases. Chrysotile kept in medium without fungi (control) gave 13.45 (plus or minus 3.28). In the table's statistical grouping, untreated chrysotile shares a letter with the no-fiber background, meaning it was not marked as statistically different from it.
  • For both fibers, incubation with each of the three fungal strains significantly reduced 8-oxodGuo formation compared with control fibers (P less than 0.05).
• The authors' conclusion: The authors concluded that their in vitro data support the idea that the weathering activity of fungi may be considered a possible strategy for remediating asbestos-rich soil. They expected that prolonged fungal action might reduce the fibers' potential to cause disease.
• Limitations the authors state:
  • DNA oxidation was detected only when EDTA was added to the test. The authors attribute the damage likely to EDTA-iron complexes.
  • DNA damage did not always match hydroxyl radical release. For example, Verticillium sp.-treated chrysotile released more radicals yet caused less DNA oxidation.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Balangero mine, Balangero, about 20 km north of Turin, Piedmont

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Crocidolite.

Medical terms in this study, explained in our Lexicon: Surface Reactivity, Chrysotile, UICC, Crocidolite, Hydroxyl Radical.

Related studies

• Weathering of chrysotile asbestos by the serpentine rock-inhabiting fungus Verticillium leptobactrum — S. Daghino, F. Turci, et al. (2009)
• Bioweathering of chrysotile by fungi isolated in ophiolitic sites — S. Daghino, E. Martino, et al. (2008)
• Iron-loaded synthetic chrysotile: a new model solid for studying the role of iron in asbestos toxicity — E. Gazzano, F. Turci, et al. (2007)
• Iron mobilization from crocidolite as enhancer of collagen content in rat lung fibroblasts — C. Gardi, P. Calzoni, et al. (1997)
• Soil fungal hyphae bind and attack asbestos fibers — E. Martino, L. Prandi, et al. (2003)
• Free radical generation in the toxicity of inhaled mineral particles: the role of iron speciation at the surface of asbestos and silica — I. Fenoglio, L. Prandi, et al. (2001)

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