Inorganic materials and living organisms: surface modifications and fungal responses to various asbestos forms

Our plain-English summary of Inorganic materials and living organisms: surface modifications and fungal responses to various asbestos forms, by S. Daghino, E. Martino, I. Fenoglio, et al (Chemistry, 2005).

The study

• Authors: S. Daghino, E. Martino, I. Fenoglio, M. Tomatis, S. Perotto, B. Fubini
• Journal: Chemistry
• Published: 2005;11(19):5611-8
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In a previous study several strains of soil fungi were reported to remove iron in vitro from crocidolite asbestos, a process that was envisaged as a possible bioremediation route for asbestos-polluted soils. Here, we get some new insight into the chemical basis of the fiber/fungi interaction by comparing the action of the most active fungal strain Fusarium oxysporum on three kind of asbestos fibers--chrysotile, amosite, and crocidolite--and on a surface-modified crocidolite. None of the fibers examined significantly inhibited biomass production. Even the smallest fibrils were visibly removed from the supernatant following adhesion to fungal hyphae. F. oxysporum, through release of chelators, extracted iron from all fibers; the higher the amount of iron at the exposed surface, the larger the amount removed, that is, crocidolite > amosite >> chrysotile. When considering the fraction of total iron extracted, however, the ranking was chrysotile > crocidolite > amosite > heated crocidolite, because of the different accessibility of the chelators to the metal ions in the crystal structure. Chrysotile was the easiest to deplete of its metal content. Iron removal fully blunted HO* radical release from crocidolite and chrysotile but only partially from amosite. The removal, in a long-term experiment, of more iron than is expected to be at the surface suggests a diffusion of ions from the bulk solid towards the surface depleted of iron by fungal activity. Thus, if the fibers could be treated with a continuous source of chelators, iron extraction would proceed up to a full inactivation of free radical release. The fungal metabolic response of F. oxysporum grown in the presence of chrysotile, amosite and crocidolite revealed that new extracellular proteins are induced--including manganese-superoxide dismutase, the typical antioxidant defense--and others are repressed, upon direct contact with the fibers. The protein profile induced by heated crocidolite was different, a result suggesting a key role for the state of the fiber/hyphae interface in protein induction.

In plain English

This laboratory study examined how the soil fungus Fusarium oxysporum interacts with asbestos. The fungus was grown for 20 days with chrysotile, amosite, crocidolite or heat-treated crocidolite, touching the fibers or separated by a membrane. None of the fibers significantly inhibited fungal growth. The fungus removed iron from all fiber types. As a share of total iron, removal with direct contact was 5.57% for chrysotile, 1.39% for crocidolite, 1.12% for amosite and 0.63% for heated crocidolite. In a 56-day crocidolite test, iron released was twice that at 20 days. Fungal treatment partly or completely inhibited hydroxyl free radical release from crocidolite and chrysotile. Results for amosite and heated crocidolite varied: in one case radical generation from amosite increased after fungal incubation, and heated crocidolite, which lacks this radical-generating ability, partly regained it in some cases. The fungus also changed the proteins it released; an antioxidant enzyme was detected in cultures with crocidolite. The authors concluded that soil fungi may provide an environment-friendly way to treat asbestos-polluted soil. They noted that real-soil and toxicity testing of treated fibers were still needed.

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 comparing the effects of one soil fungus on different asbestos fiber types
• Who was studied: Cultures of the soil fungus Fusarium oxysporum grown with UICC reference samples of crocidolite and amosite (amphiboles) and chrysotile UICC A (Rhodesian, a serpentine), plus heat-treated crocidolite. No humans or animals were studied.
• Exposure: Asbestos fibers suspended in water (1.84 g per 80 mL) and added to fungal cultures for up to 20 days (56 days in one crocidolite experiment), either in direct contact with the fungus or separated by a dialysis membrane. One crocidolite sample was heated in air for 3 hours before use.
• Main results:
  • None of the fiber types significantly inhibited growth (biomass) of the fungus.
  • The amount of iron extracted was significantly greater from the two amphiboles, crocidolite and amosite, than from chrysotile.
  • Percentage of each fiber's total iron extracted, first in direct contact with the fungus and then separated by membrane: chrysotile 5.57% and 4.62%; amosite 1.12% and 0.74%; crocidolite 1.39% and 1.19%; heated crocidolite 0.63% and 0.52%.
  • The fungus removed only about half as much iron from heated crocidolite as from the original crocidolite.
  • In a 56-day culture with crocidolite, the iron released was twice the amount released at 20 days.
  • Crocidolite that had been in contact with the fungus afterwards released substantially less iron to the chelator desferrioxamine, but iron release was not fully suppressed.
  • Fungal treatment always inhibited, partially or completely, free radical release from crocidolite and chrysotile.
  • Effects on amosite and heated crocidolite varied between experiments. In one case, radical generation from amosite increased after incubation with the fungus (data not shown).
  • Heated crocidolite, which loses its potential to generate hydroxyl radicals, partially regained that potential in some cases after incubation with the fungus, but not in others (data not shown).
  • With the fibers present, the fungus released new extracellular proteins and stopped releasing others.
  • The fungus grown with heated crocidolite showed distinctive protein bands.
  • A manganese superoxide dismutase band (an antioxidant enzyme) was identified in the culture medium of the fungus grown with crocidolite.
• The authors' conclusion: The authors concluded that soil fungi may provide an environment-friendly bioremediation approach for asbestos in soil, by continuously releasing chelators close to the fibers.
• Limitations the authors state:
  • It is not yet known whether the fungi can modify asbestos fibers in real soil.
  • The chemical nature of the chelating molecules involved in iron removal is not yet known.
  • Fungus-treated fibers still need to be tested for toxicity in cells and in living organisms.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Chrysotile, Amosite, Fibril, Crystal Structure, Superoxide.

Related studies

• Cellular response of Fusarium oxysporum to crocidolite asbestos as revealed by a combined proteomic approach — M. Chiapello, S. Daghino, et al. (2010)
• Inorganic dust pneumonias: the metal-related parenchymal disorders — P. Kelleher, K. Pacheco, et al. (2000)
• Environmental exposure to asbestos and other inorganic fibres using animal lung model — E. Fornero, E. Belluso, et al. (2009)
• In vitro genotoxicity data of nanomaterials compared to carcinogenic potency of inorganic substances after inhalational exposure — M. Roller (2011)
• High aspect ratio materials: role of surface chemistry vs. length in the historical "long and short amosite asbestos fibers" — M. Tomatis, F. Turci, et al. (2010)
• Ascorbic acid modifies the surface of asbestos: possible implications in the molecular mechanisms of toxicity — G. Martra, M. Tomatis, et al. (2003)

Browse more research in Chemistry, or return to medical research.