Rapid characterization of aquatic hyphomycetes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

ABSTRACT

Protein fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-­TOF MS) is a rapid, reliable, and economical method to characterize isolates of terrestrial fungi and other microorganisms. The objective of our study was to evaluate the suitability of MALDI-TOF MS for the identification of aquatic hyphomycetes, a polyphyletic group of fungi that play crucial roles in stream ecosystems. To this end, we used 34 isolates of 21 aquatic hyphomycete species whose identity was confirmed by spore morphology and internal transcribed spacer (ITS1-5.8S-ITS2 = ITS) nuc rDNA sequencing. We tested the efficiency of three protein extraction methods, including chemical and mechanical treatments using 13 different protocols, with the objective of producing high-quality MALDI-TOF mass spectra. In addition to extraction protocols, mycelium age was identified as a key parameter affecting protein extraction efficiency. The dendrogram based on mass-spectrum similarity indicated good and relevant taxonomic discrimination; the tree structure was comparable to that of the phylogram based on ITS sequences. Consequently, MALDI-TOF MS could reliably identify the isolates studied and provided greater taxonomic accuracy than classical morphological methods. MALDI-TOF MS seems suited for rapid characterization and identification of aquatic hyphomycete species.

KEYWORDS:

• Aquatic fungi
• ITS sequencing
• mass spectrometry
• morphology
• phylogeny
• proteomics
• taxonomy

ACKNOWLEDGMENTS

We appreciate the expert technical assistance of Anna Paola Caminada, Alison Crenna, and Valentina Alesi (Laboratory of Applied Microbiology, Bellinzona, Switzerland) in the laboratory.

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Funding

The project received financial support from the Department of Environment, Construction and Design of the Applied University of Southern Switzerland (SUPSI), and the Portuguese Foundation for Science and Technology to J.C. (FCT-SFRH/BPD/108779/2015).