Interactions of sterile-cultured lichen-forming ascomycetes with asbestos fibres

Our plain-English summary of Interactions of sterile-cultured lichen-forming ascomycetes with asbestos fibres, by S.E. Favero-Longo, M. Girlanda, R. Honegger, et al (Mycological Research, 2007).

The study

• Authors: S.E. Favero-Longo, M. Girlanda, R. Honegger, B. Fubini, R. Piervittori
• Journal: Mycological Research
• Published: 2007;111(Pt 4):473-81
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Sterile cultured isolates of lichen-forming ascomycetes have not yet been used to investigate mycobiont-mineral substrate interactions under controlled conditions. In this study Candelariella vitellina, Xanthoparmelia tinctina and Lecanora rupicola mycobionts were isolated and inoculated with chrysotile fibres in the laboratory, in order to verify whether physical and chemical weathering processes, which were already described in the field, may be reproduced in vitro. Tight adhesion of hyphae to chrysotile fibres was observed in all species. The adhering hyphae affected the chemical composition of asbestos fibres, with the selective depletion of magnesium being a prominent feature, as is the case in field conditions. Oxalic acid and pulvinic acid, mycobiont-derived metabolites of X. tinctina and C. vitellina, were involved in the weathering action. Time and environmental factors and the absence of biological synergisms strongly limited the chemical weathering in vitro compared with what was observed in the field. Nevertheless, the results show that in vitro incubation of sterile-cultured lichen-forming fungi with minerals is a practicable experimental system to investigate the weathering effects of different mycobionts and fungal compounds under controlled conditions.

In plain English

This laboratory experiment tested whether lichen-forming fungi could reproduce, in culture, the weathering of chrysotile asbestos fibres that an earlier field study had described. The authors collected thalli of three lichen species (Candelariella vitellina, Lecanora rupicola and Xanthoparmelia tinctina) from asbestos-rich serpentinite rocks in the Western Italian Alps in spring 2003, mostly at the abandoned Balangero mine. They grew the fungal partner of each lichen alone in sterile culture on plates with sterilized chrysotile fibres from that mine. After 15 months, hyphae of all three species clung closely to the fibres and occasionally penetrated fibre bundles. L. rupicola and X. tinctina released oxalic acid, and C. vitellina released pulvinic acid. Only fibres touching X. tinctina differed significantly from control fibres. They lost magnesium oxide, and their average silica-to-magnesium oxide ratio was 1.28, compared with 1.02 in controls. Changes with the other two species were not significant, and only some fibres changed. The authors concluded that the method only partly reproduced field weathering but is a practicable experimental system.

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 growing lichen fungi on chrysotile fibres, compared with fibres on sterile agar and with untreated fibres. No people or animals were studied.
• Who was studied: Thalli of Candelariella vitellina (16), Lecanora rupicola subsp. subplanata (10) and Xanthoparmelia tinctina (7). They were collected in spring 2003 on asbestos-rich serpentinites in the Western Italian Alps, mainly at the abandoned Balangero mine, and the fungal partners (mycobionts) were isolated in sterile culture.
• Exposure: Sterilized (autoclaved) chrysotile asbestos fibres from the Balangero mine, scattered on nutrient agar plates with the fungal cultures. Fibres were analysed chemically after 15 months.
• Main results:
  • After 15 months, hyphae of all three species were in close physical contact with the chrysotile fibres. Occasionally the hyphae penetrated fibre bundles and broke up their structure.
  • Control fibres kept on sterile agar did not differ significantly in composition from untreated chrysotile.
  • Fibres in contact with X. tinctina (8 fibres analysed) showed a significant decrease in magnesium oxide content and a relative increase in silica, compared with controls. P-values were: silica, p less than 0.023; magnesium oxide, p less than 0.007; silica-to-magnesium oxide ratio, p less than 0.004.
  • For X. tinctina-contacted fibres, the average silica-to-magnesium oxide ratio rose from 1.02 (controls) to 1.28.
  • Fibres in contact with L. rupicola (8 fibres) and C. vitellina (13 fibres) showed no significant change compared with controls. For C. vitellina the average ratio changed by 13.8% (from 1.02 to 1.16); for L. rupicola the change was 3.8%.
  • Only some fibres in contact with hyphae showed chemical change; others showed none after 15 months.
  • In culture, L. rupicola and X. tinctina secreted oxalic acid, which formed calcium and magnesium oxalate crystals.
  • In culture, C. vitellina secreted no oxalate but produced crystals identified as pulvinic acid.
  • For comparison, the authors recalculated data from their own earlier field study. In that study, lichen-colonized chrysotile showed an average 22.2% increase in the silica-to-magnesium oxide ratio over fibres not in contact with lichens.
• The authors' conclusion: The authors concluded that growing sterile-cultured lichen-forming fungi with minerals is a practicable experimental system for studying weathering. They attributed the weathering by X. tinctina and C. vitellina most likely to oxalic and pulvinic acid, respectively.
• Limitations the authors state:
  • The laboratory system only partially reproduced the processes seen at the lichen-rock interface in the field.
  • Fibres in the field were exposed to fungal chemicals for much longer than in the experiment.
  • The experiment lacked other fungi and microbes that may speed weathering in nature.
  • The fungi grew slowly, so long-term experiments are needed.
  • The culture conditions did not induce production of the typical lichen substances in two of the three species.
  • With percentage composition data, a loss of one constituent makes the others appear to increase.

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

Medical terms in this study, explained in our Lexicon: Chrysotile.

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