Abstract
Available genomic data for the toxic, bloom-forming, benthic Ostreopsis spp. are traditionally obtained from isolates rather than from individuals originally present in environmental samples. Samples from the final phase of the first reported Ostreopsis bloom in European North Atlantic waters (Algarve, south coast of Portugal) were studied and characterized, using a culture-independent approach. In the first instance, a microscopy-based analysis revealed the intricate complexity of the samples. Then, we evaluated the adequacy of commonly used molecular tools (i.e., primers and nuclear ribosomal markers) for the study of Ostreopsis diversity in natural samples. A PCR-based methodology previously developed to identify/detect common Ostreopsis species was tested, including one new combination of existing PCR primers. Two sets of environmental rRNA sequences were obtained, one of them (1052 bp) with the newly tested primer set. These latter sequences encompass both the ITS1-5.8S-ITS2 region and the D1/D2 domain of the LSU rRNA gene, leading us to an accurate identification of ITS2. In turn, this allowed us to predict and show for the first time the ITS2 secondary structure of Ostreopsis. With 92 bp in length and a two-helix structure, the ITS2 of this genus revealed to be unique among the dinoflagellates. Both the PCR approach as the phylogenetic analyses allowed to place the Ostreopsis cells observed in the samples within the O. cf. ovata phylospecies’ complex, discarding the presence of O. cf. siamensis. The (phylo)genetic results point out a certain level of nucleotide sequence divergence, but were inconclusive in relation to a possible geographic origin of the O. cf. ovata population from the Algarve’s bloom.
Highlights
The harmful algal bloom (HAB)-forming Ostreopsis ovata Fukuyo and Ostreopsis siamensis Schmidt are toxic, benthic dinoflagellates species recognized as being distributed from tropical to temperate coastal waters [1], with increasingly frequent appearances in different regions of the Mediterranean basin [2]
Cells assigned to Ostreopsis sp. were ovoid to teardrop-shaped in dorsoventral (DV) view, with many golden chloroplasts radially disposed (Figure 1B,C)
Morphometric values presented by the Algarve’s Ostreopsis cells were comparable with those from environmental or cultured Ostreopsis cf. ovata and Ostreopsis cf. siamensis cells obtained from other studies (Table 1)
Summary
The harmful algal bloom (HAB)-forming Ostreopsis ovata Fukuyo and Ostreopsis siamensis Schmidt are toxic, benthic (including epibenthic, epiphytic, or tychoplanktonic) dinoflagellates species recognized as being distributed from tropical to temperate coastal waters [1], with increasingly frequent appearances in different regions of the Mediterranean basin [2]. These two species are known to co-occur [3,4] their morphological differentiation is quite difficult. The occurrence of O. cf. siamensis and/or O. cf. ovata in Portugal (including Azores and Madeira Islands) is known from monitoring studies and anecdotal reports [14,16,17,18] or from the existence of isolates collected in Portuguese waters [19,20]
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