The marine diatom Pseudo-nitzschia galaxiae Lundholm et Moestrup has been recently described from Mexican and Australian plankton. In this paper we illustrate the considerable morphological variability of the species in the Mediterranean Sea and present first evidence of its toxicity. In addition to lanceolate cells 25-41 μm long, which fit the original description of the species, markedly larger (< 82 μm) and smaller (> 10 μm) specimens are commonly recorded. Cells of the largest size have almost parallel valve margins, while smaller specimens have extremely short rostrate ends and do not form colonies. Despite remarkable differences in shape and size, the typical ultrastructure of the species was observed for the different size classes in culture and in natural samples. LSU rDNA analysis confirmed the identity of the species and showed a very low genetic variability for the strains from the Gulf of Naples, with no relationships with size and overall shape of the cells. Despite the relatively high number (53) of Pseudo-nitzschia sequences considered in the phylogenetic analysis, the relationships among species remain unclear, probably in relation with a recent speciation process in the genus. LC-MS analyses revealed the presence of domoic acid at very low levels in two of seven strains analysed. In natural samples, P. galaxiae populations of different cell size occurred at different time over the year, with smaller cells typically found in winter and early spring, and medium and larger cells peaking in late spring-summer. The maximum concentration value was recorded in May 1985 (9.4•106 cells l-1). It is concluded that size and shape variations are indicative of different stages of the life cycle of P. galaxiae, which exhibit a synchronised and seasonal occurrence at the interannual scale.

The alteration of different morphotypes in the seasonal cycle of the toxic diatom Pseudo-nitzschia galaxiae

DELL'AVERSANO, CARMELA;TARTAGLIONE, LUCIANA;
2005

Abstract

The marine diatom Pseudo-nitzschia galaxiae Lundholm et Moestrup has been recently described from Mexican and Australian plankton. In this paper we illustrate the considerable morphological variability of the species in the Mediterranean Sea and present first evidence of its toxicity. In addition to lanceolate cells 25-41 μm long, which fit the original description of the species, markedly larger (< 82 μm) and smaller (> 10 μm) specimens are commonly recorded. Cells of the largest size have almost parallel valve margins, while smaller specimens have extremely short rostrate ends and do not form colonies. Despite remarkable differences in shape and size, the typical ultrastructure of the species was observed for the different size classes in culture and in natural samples. LSU rDNA analysis confirmed the identity of the species and showed a very low genetic variability for the strains from the Gulf of Naples, with no relationships with size and overall shape of the cells. Despite the relatively high number (53) of Pseudo-nitzschia sequences considered in the phylogenetic analysis, the relationships among species remain unclear, probably in relation with a recent speciation process in the genus. LC-MS analyses revealed the presence of domoic acid at very low levels in two of seven strains analysed. In natural samples, P. galaxiae populations of different cell size occurred at different time over the year, with smaller cells typically found in winter and early spring, and medium and larger cells peaking in late spring-summer. The maximum concentration value was recorded in May 1985 (9.4•106 cells l-1). It is concluded that size and shape variations are indicative of different stages of the life cycle of P. galaxiae, which exhibit a synchronised and seasonal occurrence at the interannual scale.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/102966
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