Friday 14 January 2 pm GMT+1
Takuto ANDO1*, Kazumi MATUOKA2, Karin ZONNEVELD3, Gerard VERSTEEGH4, Mika ISHIGAKI5, Tatsuyuki YAMAMOTO6
Macromolecules analyses of cyst wall of Alexandrium catenella/pacificum using ATR-FTIR and Raman spectroscopy
1 Estuary Research Center, Shimane University, Matsue, Japan
2 Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan
3 Center for Marine Environmental Sciences (MARUM), Bremen University, Bremen, Germany
4 Marine Biochemistry Section, Alfred-Wegener-Institute, Bremerhaven, Germany
5 Center for Promotion of Project Research. Shimane University, Matsue, Japan
6 Faculty of Life and Environmental Sciences, Shimane University, Matsue, Japan
Blooms (red-tides) caused by dinoflagellates, especially toxic/harmful species, in coastal waters adversely impact both marine ecosystems and human health. Formation of dinocysts and their preservation in the sediments are therefore essential subjects for understanding the bloom mechanisms. Alexandrium catenella/pacificum are toxic species (paralytic shellfish poisoning) that produce elliptical transparent cysts. These cysts are generally rather labile than those of other gonyaulacoid cysts. The lability of dinocysts during early diagenesis is related to, as yet largely unknown, differences in macromolecular composition. Macromolecular analysis using micro-FTIR may shed light on the preservation/decomposition process of palynomorphs. Raman microscopy is another spectroscopic method to observe the macromolecular structure and can obtain a micron- or submicron resolution. However, it is difficult to get good spectra due to emission of autofluorescence from targeted palynomorphs using light with short wavelengths (e.g., 532 nm laser). In this presentation, we present the results of both ATR-FTIR and micro-Raman analysis of the cyst of Alexandrium catenella/pacificum.
IR spectra of A. catenella/pacificum cysts are characterized by a dominant absorption band between 1200-1000 cm-1 and weak bands between 1450-1200 cm-1 and 1800-1600 cm-1. Cluster analysis of the IR spectra for wave lengths between 800-1800cm-1 suggest that the macromolecular structure of A. catenella/pacificum cysts is very close to cellulose. However, the highest peak in the spectra of A. catenella/pacificum cysts in the 1200-1000 cm-1 window is at ~1033cm-1 and lower than for cellulose (~1059 cm-1). The Raman spectra (with using a 785 nm laser) for these cysts show main peaks around 1050-1170 cm-1 and these overlap with those of cellulose. The Raman spectra of A. catenella/pacificum cyst also include the higher peaks around 1500-1200 cm-1 region and show a moderate peak at 898 cm-1, which are characteristics of polysaccharides with 1,6- and β-glucoside bonds, respectively. We therefore suggest that the macromolecules in the cyst of A. catenella/pacificum are composed of the polysaccharide with β-1,4-glucoside bonds including smaller number of β-1,6-glucoside bonds. These data suggest the cyst of A. catenella/pacificum is susceptible to decomposition by cellulase compared to other gonyaulacoid dinocysts.