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

Sterile cultured isolates of lichen-forming ascomycetes have not yet been used to investigate mycobiont-mineralsubstrate interactionsunder controlledconditions. Inthis 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, whichwere already described in the field,maybe 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 magnesiumbeing 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 showthat 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.