The Silent Threat: Impact of Aspergilli Spores on Biodeterioration of Cultural Heritage

BACKGROUND AND OBJECTIVESAspergillus species possess a remarkable ability to grow in a multitude of environmental conditions. They disseminate through the production of large numbers of asexual spores called conidia. These spores are airborne and remain dormant until encountering favorable conditions for growth, such as optimal humidity, temperature, and nutrient availability. Upon finding these conditions, germination ensues, characterized by cellular swelling and the emergence of a germ tube.Aspergillus spores are ubiquitous in cultural heritage environments due to their widespread distribution and resilience. Upon germination, the resulting hyphae can secrete acids and a plethora of enzymes that contribute to material degradation. Here we studied the minimal nutrient requirements for germination of conidia of aspergilli to assess whether these can be used to control the biodeterioration of cultural heritage.MATERIALS AND METHODSWe studied the germination of conidia of five Aspergillus species: A. niger, A. oryzae, A. clavatus, A. nidulans, and A. terreus. Utilizing the oCelloScope imager and computational models, we analyzed their minimal nutrient requirements for germination, in particular using amino acids as signaling molecules and/or carbon source. We examined germination in pure water and observed the effects of various nutrients, including glucose, phosphate, nitrate, and sulfate.RESULTS AND DISCUSSIONOur study revealed varying germination potentials among the five Aspergillus species in both pure water and nutrient-supplemented conditions. For instance, A. clavatus and A. nidulans were able to germinate in pure water, while A. niger conidia required a combination of an inducing carbon source and either inorganic phosphate, nitrogen, or magnesium sulfate for germination. Alanine and proline were found to be the most effective in inducing germination in most species except A. terreus. In contrast, leucine, isoleucine, cysteine, and methionine were generally the least effective. Results showed that not only the nutrient composition affected germination incidence but also the spore concentration. In fact, both inter- and intra-species heterogeneity was observed in the latter case. Results indicate that spores of Aspergillus ۳۵use a bet-hedging strategy. Only part of the spores germinate. This ensures that the substrate can be colonized by the germlings on the one hand, but that stress-resistant spores are still present that ensure survival when humidity or nutrient conditions change.CONCLUSIONOur findings suggest that Aspergilli exhibit distinct competitive potentials across different substrates, utilizing a bet-hedging strategy in their germination response. Also notable, spores of Aspergillus can inhibit the germination of their own and that of other species. These insights are crucial for understanding the biodeterioration risks posed by Aspergillus, particularly in the context of cultural heritage preservation. The fact that spores of different aspergilli respond differently to environmental conditions hampers a generalized control of their germination to prevent damage of cultural heritage.

کلیدواژه ها:

Aspergillus ، Germination ، Spore ، Biodeterioration ، Cultural Heritage