DIVERSITY OF PSEUDO-NITZSCHIA IN THE SOUTHEASTERN BAY OF BISCAY

Abstract

Ten species of the genus Pseudo-nitzschia were identified in the Nervion River estuary from preserved net tow samples and 31 strains isolated from the estuary. Species identification was performed by means of ultrastructural analysis of valve ornamentation and genetic analysis of selected strains of the P. delicatissima complex. Identified species include: P. australis, P. fraudulenta, P. pungens and P. subpacifica from the P. seriata complex, and P. arenysensis, P. galaxiae, P. multistriata, P. pseudodelicatissima and two uncertain P. pseudodelicatissima-like genotypes from the delicatissima complex. Most clonal strains corresponded to P. pseudodelicatissima-like taxa, P. fraudulenta and P. galaxiae. We were unable to identify the strains of the P. delicatissima-like complex solely on the basis of morphology. A comparison of sequences of the rDNA ribosomal Internal Transcribed Spacers (ITS), including the regions ITS1, 5.8S and ITS2, of four strains of the P. delicatissima complex plus 23 sequences of taxonomically related strains available in GenBank, revealed the presence of P. arenysensis among strains of the P. delicatissima-morphologies and three different ITS types among the three P. pseudodelicatissima-like morphologies analysed. One corresponded to P. pseudodelicatissima sensu stricto (strain Ner-D5) whereas the other two (Ner-D6 and Ner-D8) constituted genetically distinct entities, which appeared in the phylogenetic tree as sister taxa to either P. cuspidata, the former, or to P. calliantha and P. mannii, the latter. The genetic differences among these three strains of P. pseudodelicatissima-like morphologies were corroborated by analysing their ITS2 secondary structure and comparing them with the ITS2 secondary structure of phylogenetically related species from GenBank.