Species determination and characterisation of developmental stages of ticks by whole animal matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS)
Classically, ticks and their developmental stages are differentiated by morphological criteria. However, molecular biological methods, such as PCR using mitochondrial 12S and 16S rDNA sequences, have been applied increasingly in tick identification. A very cost-efficient and rapid, yet highly informative tool for tick species determination could be whole animal matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) based on protein spectra which over the past few years has been introduced successfully for the identification and classification of bacteria and also for tissue cultures.
Here, a simple protocol was developed to perform MALDI-MS analysis on extracts from whole ticks. A reference database of spectra was constructed for seven species (I. canisuga, I. hexagonus, I. persulcatus, I. ricinus, I. scapularis, D. reticulatus und R. sanguineus).
Cluster analysis on the basis of MALDI mass spectra indicated that the primary determinant for the mass spectra was the species, followed by the developmental stages, which formed distinct clusters within the given species.
Clusters illustrated phylogenetic correlations between species. With certain limitations, species identification was also possible using “problematic samples” such as body parts (not possible with only legs) and engorged animals. Spectra of developing Ixodes ricinus eggs during 39 days showed dramatic changes with time.
Spectra of ticks were compared with regard to environmental, temporal and local influences. It could be shown that especially environmental (forest or meadow) and temporal (season) factors influenced tick spectra.
So far, the reasons for these changes and their importance are not known, however, it is possible that, beyond its usefulness for species determination, MALDI-MS may provide insights into the developmental biology of ticks with its supporting and limiting factors.