Optimising a MALDI-TOF MS database for the detection of xerophilic fungi across environments

Xerophilic fungi can proliferate in dry conditions and have been detected in cultural heritage sites and libraries. To protect the staff from fungal exposure and ensure the preservation of heritage collections, research must be focused on improving detection protocols for xerophilic fungi. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry provides a strong method for the identification of fungi; however, this is dependent on the reference database. The aim of this study was to investigate whether it is possible to develop a supplementary matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry database of xerophilic/xerotolerant Aspergillus species. The database is intended to complement the current Bruker library; for this 19 Aspergillus species grown in four different broth media were included. The database was evaluated on samples from domestic homes, a museum and a warehouse. It was possible to create a database with mass spectra from the 19 species. For some species, it was possible to generate mass spectra from the four tested broth media, while other species required specific media and extended incubation time. Isolates from environmental samples identified by the Bruker fungi library were not misidentified by the supplementary database while some previously unidentified isolates (Aspergillus conicus, Aspergillus domesticus, Aspergillus glabribes and Aspergillus pseudogracilis) could be identified. Using low water-activity agar media had a profound effect on detection of these xerophilic/xerotolerant Aspergillus species. This work shows that it is possible to develop a supplementary matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry database for the identification of xerophilic/xerotolerant Aspergillus species, and that low-water activity broth media are recommended for the construction of a database and the following application.