Multiple rDNA ITS-types within the diatom Pseudo-nitzschia delicatissima (Bacillariophyceae) and their relative abundances across a spring bloom in the Gulf of Naples

Abstract

The genus Pseudo-nitzschia includes a number of species responsible for blooms in coastal and open waters worldwide. P. delicatissima, a species reported as a potential source of amnesic shellfish poisoning (ASP), reaches high concentrations in the Gulf of Naples (Mediterranean Sea), where it regularly blooms in spring and, at times, in autumn. We assessed both intra-and interindividual genetic diversity of this species before and during a bloom (February to April 2001) by sequencing the internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S gene of the nuclear ribosomal DNA. PCR products obtained from 70 strains were cloned and several ITS copies were sequenced for each strain to assess intra-individual polymorphism. Phylogenies showed the presence of 5 distinct, well-supported lineages within what was considered to be a single morphospecies. Genetic diversity was higher in pre-bloom conditions, while all strains collected at the height of the bloom clustered within a single major clade. Ultrastructural investigations carried out on selected strains revealed morphological features slightly different from the ones typical for P. delicatissima only in 1 strain, outside the major clade. Our results, supported by the analysis of the hypervariable domains of LSU (large subunit) rDNA carried out on selected strains, suggest the presence of cryptic diversity within P. delicatissima. Such diversity could in fact explain the existence of toxic and nontoxic strains within the same species and the occasional mismatches between 'species-specific' molecular probes and target species.

Biogeography of the uncultured marine picoeukaryote MAST-4: temperature-driven distribution patterns

“…In our study, we used the highly variable ITS1 region as a diversity marker, which provides an enhanced taxonomic resolution as compared with the 18S rDNA gene (Brown and Fuhrman, 2005). ITS1 has been used to assess the inter-and intraspecific diversity of Pseudo-nitzschia populations (Orsini et al, 2004) and for elucidating Pseudo-nitzschia community structure using ARISA fingerprints (Hubbard et al, 2008). Our analysis using both the ITS1 sequences and ARISA fingerprints confirmed the ITS region as a good marker for studying microbial biogeography.…”

Congruence of morphological, reproductive and ITS rDNA sequence data in some AustralasianEunotia bilunaris(Bacillariophyta)

“…The present investigation represents a new addition to a still very short list of studies in which clones from geographically distant areas have been successfully mated, and an even shorter list where crossing experiments have been combined with molecular analyses: those investigated are a few members of the raphid pennate genera Sellaphora and Achnanthes (Mann, 1999;Behnke et al, 2004), and Pseudo-nitzschia (Amato et al, 2005;Orsini et al, 2004;Casteleyn et al, 2004;Chepurnov et al, 2005). Eunotia bilunaris is particularly suited to this kind of study, because it has been reported over a broad geographical area and is often abundant where it occurs.…”

“…Revision of species taxonomy in diatoms increasingly requires a rigorous, multidisciplinary approach incorporating crossing experiments and molecular genetic analysis, as well as careful morphological analysis (e.g. Mann, 2001;Behnke et al, 2004;Orsini et al, 2004;Amato et al, 2005;Sarno et al, 2005).…”

“…Taken together and applied to sufficiently large samples, these approaches can reveal species limits and relationships in hitherto intractable genera (e.g. Behnke et al, 2004;Orsini et al, 2004;Amato et al, 2005). Recently, during ongoing investigations of the freshwater diatom flora in Australasia (e.g.…”

“…As a molecular marker, we selected the ITS region, which has already proved to be useful for species-level comparisons in other diatoms (e.g. Zechman et al, 1994;Lundholm et al, 2003;Behnke et al, 2004;Orsini et al, 2004).…”