Morphology, phylogeny and toxin analysis of Pseudo-nitzschia pseudodelicatissima (Bacillariophyceae) isolated from the Thermaikos Gulf, Greece

Abstract

Moschandreou K.K., Papaefthimiou D., Katikou P., Kalopesa E., Panou A. and Nikolaidis G. 2010. Morphology, phylogeny and toxin analysis of Pseudo-nitschia pseudodelicatissima (Bacillariophyceae) isolated from the Thermaikos Gulf, Greece. Phycologia 49: 260–273. DOI: 10.2216/09-42.1

Pseudo-nitzschia pseudodelicatissima is a diatom species that has been associated with the production of the neurotoxin domoic acid (DA), causative agent of amnesic shellfish poisoning. However, the taxonomic revision of this species complex resulted in uncertain identity and, subsequently, toxicity of the strains tentatively identified under light microscope as P. pseudodelicatissima. Six strains isolated from the Thermaikos Gulf during the period from August to October 2008 were cultured and tested for production of DA. All strains were studied in morphological detail using electron microscopy and were identified as P. pseudodelicatissima. The identification was supported by phylogenetic analyses of the large subunit (LSU) and internal transcribed spacer (ITS) ribosomal rDNA regions, along with the secondary structure of ITS-2 rDNA region. DA was detected in all cultures and in three of the strains in quantifiable amounts up to 3.08 ng ml⁻¹. Two of the strains were studied over the course of a batch culture growth experiment and DA was detected from the mid-exponential until late-stationary phases; the maximum whole-culture DA levels were measured in late-exponential to early-stationary phases. This study confirms the production of DA by P. pseudodelicatissima in culture.

Key Words::

• Domoic acid
• ITS rDNA
• LSU rDNA
• Pseudo-nitzschia pseudodelicatissima
• Thermaikos Gulf

ACKNOWLEDGMENTS

The authors are grateful to Professor E. P. Eleftheriou and I.-D. S. Adamakis for their contribution with transmission electron microscopy. This work is part of the PhD thesis (School of Biology, Aristotle University of Thessaloniki) of K.K.M.