Abstract
Pseudo-nitzschia pungens is a common component of the phytoplankton community of the northern Adriatic Sea. In this study, an in-depth morphological analysis of P. pungens was carried out in both cultured strains isolated in different periods and field samples, revealing a surprisingly wide variability in a number of details, with both the gross morphology and ultrastructural levels deviating from the nominal P. pungens. Colonies showed an overlap (from one-third to one-sixth) and a transapical axis (rarely reaching 3 µm), strongly differing from the original description of the species. Moreover, valves may be either symmetrical or slightly asymmetrical, with striae almost always biseriate but sometimes uniseriate or triseriate. Poroids’ morphology in cingular bands was characterized by a wide variability (square, circular, or rectangular poroids without or with up to two hymen sectors), with several combination of them, even within the same cingular band. Phylogenetic analyses based on ITS rDNA showed that the P. pungens of the northern Adriatic Sea belonged to clade I. Domoic acid was not detected.
Highlights
Planktonic diatom species of the genus Pseudo-nitzschia are recorded in coastal regions worldwide.Among the 53 known species [1], 26 have been shown to produce domoic acid (DA) [2,3], causing neurologic disorders and memory loss in vertebrates linked to the consumption of contaminated shellfish (Amnesic Shellfish Poisoning) [4,5]
Species of the genus Pseudo-nitzschia have been subdivided in two light microscope (LM)-discernible groups based on cell width in valve view: All the species wider than 3 μm have been combined into the seriata group, while those less than 3 μm are in the delicatissima group [18]
All the morphometric measurements have been performed with electron microscopy (EM), except for the Apical Axis (AA) measured both in LM
Summary
Among the 53 known species [1], 26 have been shown to produce domoic acid (DA) [2,3], causing neurologic disorders and memory loss in vertebrates linked to the consumption of contaminated shellfish (Amnesic Shellfish Poisoning) [4,5]. In this genus, the number of genetic lineages is markedly higher than the number of taxa discernible by light microscope (LM). The combination of a few morphological characters (including cell size, overlap of cells in colonies [22]) has usually been enough to distinguish P. pungens from other
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