Tracking diversity, metabolic activity, and bioactive metabolites of the building mycobiota – examples and novel findings

Marja Johanna Salo

Research output: ThesisDoctoral ThesisCollection of Articles


Fungal growth in a building may cause decay of building materials and health effects on building users. Growth conditions affect the diversity of fungal species, the production of fungal metabolites, and the formation of guttation droplets, of which the contents and effects are still largely unknown. This study aimed to track the diversity and toxicity of the fungal species found in premises related to former moisture damages and health complaints of the occupants, demonstrate the guttation of metabolites by actively growing filamentous fungi, and design a method for detecting the transition of the fungal metabolites. In addition, the study aimed to evaluate fast microscopic and toxicological methods for monitoring metabolic activity in some common indoor fungi and to reveal the metabolic difference between fresh, actively growing, and old, desiccated, dormant colonies growing in building materials and culture media. Fungal colonies from the cultivated samples of the settled indoor dust and building materials were screened for toxicity and identified. Most individual colonies (>70% of tested colonies) in the samples collected from the rooms with indoor air-related health complaints proved toxic with the bioassays used. Many of the toxigenic species found in indoor settled dust were also detected in the insulation material of the building envelope next to the same room. Indoor isolates of Penicillium expansum, Acrostalagmus luteoalbus, and Aspergillus calidoustus, rarely or not earlier reported indoor, produced mycotoxins: communesins A, B, and D and chaetoglobosin C; melinacidins II, III, and IV; and ophiobolins G, H, and K and 6-epi-ophiobolin K, respectively. The guttation phenomenon was observed for toxigenic Pen. expansum, Acr. luteoalbus, Asp. calidoustus, and Chaetomium globosum. Pen. expansum formed guttation droplets even when growing on building material. The guttation droplets of Pen. expansum strain RcP61 (grown on MEA) were highly toxic, contained communesins A, B, and D (at the concentration of 86 µg communesins (in total) per mL of exudate) and chaetoglobosin C (480 µg toxin per mL of exudate), and proved to be more toxic than biomass extracts (containing 10 mg dry wt per mL) of the same strain. A simple test arrangement revealed the transition of the guttation droplets carrying conidia and secondary metabolites such as toxins, hydrophobics, and surfactants from mycelia to the inner surface of the lid of the Petri dish through the air. The transition of the mycotoxins communesins and chaetoglobosin A produced by an indoor isolate of Pen. expansum was confirmed using HPLC-MS analysis. Viability staining, illuminating with UV light, and bioassays revealed differences between dehydrated and actively growing fungal biomass. The old, dry dormant fungal biomass emitted less fluorescence after viability staining and UV excitation, contained fewer guttation droplets, and showed a weaker response in toxicity tests than the actively growing fungal biomass. This result indicates that the emissions of fungal metabolites into indoor air may depend on the metabolic state of the indoor filamentous fungi colonising a building.
Translated title of the contributionRakennuksen homesienilajiston monimuotoisuuden ja bioaktiivisten aineenvaihduntatuotteiden kartoitus – esimerkkejä ja uusia havaintoja
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Salonen, Heidi, Supervising Professor
  • Andersson, Aino, Thesis Advisor
Print ISBNs978-952-64-0929-0
Electronic ISBNs978-952-64-0930-6
Publication statusPublished - 2022
MoE publication typeG5 Doctoral dissertation (article)


  • building mycobiota
  • guttation droplets
  • bioactive fungal metabolites
  • indoor filamentous fungi


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