Indoor Strains of Aspergillus Calidoustus and Aspergillus Versicolor Emit Mycotoxins in Guttation Droplets

Active mold growth indoors is considered a health threat, and there is consensus that inhaling mold can cause health problems for people. However, why active mold growth is a more serious threat than the presence of dried, inactive mycelia (1) and how metabolically active molds release hazardous substances into indoor air is still a matter of debate. In other words, there is consensus that inhalation exposure to molds can cause human health problems (2), but the point at which indoor microbial contamination harms human health is not yet understood. In this study, we show that actively growing Aspergillus strains belonging to the species A. calidoustus and A. versicolor secrete mycotoxins in guttation droplets. Guttation enables the release of metabolic products into the environment and is associated with active fungal growth. The mycotoxins secreted by A. calidoustus were identified by LC-MS as ophiobolin H and G. A. versicolor strains secreted sterigmatocystin, 5-methoxysterigmatocystin and averufin. These metabolites have previously been detected in biomass extracts of indoor strains of A. calidoustus and A. versicolor (3). Toxic secondary metabolites in guttation droplets have previously also been detected in indoor Penicillium Trichoderma (4) and Chaetomium strains (5), but to our knowledge, this is the first time they have been found in guttation droplets secreted by indoor Aspergillus strains. We speculate that the guttation of these metabolites may contribute to the indoor air load of hazardous substances in polluted buildings. We suggest that the presence of mycotoxins, i.e. as sterigmatocystin produced by A. versicolor, a known indicator of indoor water damage, justifies this mold's bad reputation.

References
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