AB 20:139-144 (2014)  -  DOI: https://doi.org/10.3354/ab00548

ABSTRACT: Diatom identification is based on classical morphological methods focused on frustule shape and ornamentation analysis and possible chain formation. Because many morphological aspects are common to several species, diatom identification and characterisation are time-consuming and demand significant expertise. Furthermore, the use of advanced microscopy, such as transmission electron microscopy or scanning electron microscopy, is frequently necessary to differentiate these organisms. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was used to differentiate diatom taxa, and this report presents a preliminary study of the possibility of using this technique to obtain reliable fingerprinting of diatoms in the range of 2 to 20 kDa. Seminavis robusta, Coscinodiscus sp., Thalassiosira sp. and Cyclotella meneghiniana were used. The influence of culture age on reproducibility was studied. MALDI-TOF MS spectra were shown to vary with culturing time, and the need to consider this when setting up experimental standard conditions in the identification of diatoms was clearly established. One of the most important observations was that each diatom strain presented a specific age when the mass spectrum became reproducible. For all S. robusta strains and for C. meneghiniana, this age was 9 d, and for Thalassiosira sp. and Coscinodiscus sp., this age was 13 d. Even with the limitations of culture aging versus spectra reproducibility, MALDI-TOF MS proved to be a useful complementary tool to identify and characterise diatoms at the genus level. However, it was not possible to distinguish different mating types within the same species, as evidenced by the results obtained with S. robusta isolates.

KEY WORDS: Diatoms · MALDI-TOF MS · Culture age