Fungal pigments inhibit the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of darkly pigmented fungi

National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV 26505, USA.
Analytical Biochemistry (Impact Factor: 2.22). 04/2011; 411(1):122-8. DOI: 10.1016/j.ab.2010.11.025
Source: PubMed


Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been used to discriminate moniliaceous fungal species; however, darkly pigmented fungi yield poor fingerprint mass spectra that contain few peaks of low relative abundance. In this study, the effect of dark fungal pigments on the observed MALDI mass spectra was investigated. Peptide and protein samples containing varying concentrations of synthetic melanin or fungal pigments extracted from Aspergillus niger were analyzed by MALDI-TOF and MALDI-qTOF (quadrupole TOF) MS. Signal suppression was observed in samples containing greater than 250ng/μl pigment. Microscopic examination of the MALDI sample deposit was usually heterogeneous, with regions of high pigment concentration appearing as black. Acquisition of MALDI mass spectra from these darkly pigmented regions of the sample deposit yielded poor or no [M+H](+) ion signal. In contrast, nonpigmented regions within the sample deposit and hyphal negative control extracts of A. niger were not inhibited. This study demonstrated that dark fungal pigments inhibited the desorption/ionization process during MALDI-MS; however, these fungi may be successfully analyzed by MALDI-TOF MS when culture methods that suppress pigment expression are used. The addition of tricyclazole to the fungal growth media blocks fungal melanin synthesis and results in less melanized fungi that may be analyzed by MALDI-TOF MS.

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Available from: Don H Beezhold, Jun 13, 2014
    • "During the analysis of darkly pigmented spores or cell material the melanin diminishes the ionization capability of the MALDI matrix by interfering with the energy transfer from the matrix to the sample molecules. The melanin compounds act as an energy sink (Buskirk et al., 2011). Thus, sample molecules are ionized poorly due to an insufficient energy transfer. "
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    • "Knowing that the black or dark brown pigmented fungi are almost always associated with melanin which is known to absorb portion of visible and UV light, the lack of data may be attributed to the characteristics of the pigment. Attempts to analyze them by massspectroscopy by other researchers yield poor fingerprint spectra (Buskirk et al., 2011; Bochenek and Gudowska- Nowak, 2003). Advancements of phytophotobiology will benefit other fields concerned with dark pigmented fungi. "
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