Recommendations for epitypification of dinophytes exemplified by Lingulodinium polyedra and molecular phylogenetics of the Gonyaulacales based on curated rRNA sequence data

Gonyaulacales include a considerable number of harmful algae and to understand their origin and rise, knowledge of the evolutionary relationships is necessary. Many scientific names of protists introduced prior to the availability of DNA analytics are ambiguous and impede communication about biological species and their traits in the microbial world. Strains of Lingulodinium polyedra were established from its type locality in the Kiel Fjord (Germany) to clarify its taxonomy. Moreover, the phylogeny of Gonyaulacales was inferred based on 329 rRNA sequence accessions compiled in a curated sequence data base, with as much as possible type material equivalents included. Gonyaulacales were monophyletic and segregated into seven lineages at high systematic level, of which †Lingulodiniaceae constituted the first branch of the Gonyaulacales. Their type species had a plate formula APC (Po, X, cp), 3', 3a, 6'' 6c, 6s, 6''', 2'''' and is taxonomically clarified by epitypification. Recommendations for this important taxonomic tool are provided, with a focus on microorganisms. Most gonyaulacalean taxa established at generic rank are monophyletic, with Alexandrium, Coolia and Gonyaulax as notable exceptions. From an evolutionary perspective, gonyaulacalean dinophytes with quinqueform hypotheca are monophyletic and derive from a paraphyletic group showing the sexiform configuration.

Morphological and phylogenetic data do not support the split of Alexandrium into four genera

A recently published study analyzed the phylogenetic relationship between the genera Centrodinium and Alexandrium, confirming an earlier publication showing the genus Alexandrium as paraphyletic. This most recent manuscript retained the genus Alexandrium, introduced a new genus Episemicolon, resurrected two genera, Gessnerium and Protogonyaulax, and stated that: "The polyphyly [sic] of Alexandrium is solved with the split into four genera". However, these reintroduced taxa were not based on monophyletic groups. Therefore this work, if accepted, would result in replacing a single paraphyletic taxon with several non-monophyletic ones. The morphological data presented for genus characterization also do not convincingly support taxa delimitations. The combination of weak molecular phylogenetics and the lack of diagnostic traits (i.e., autapomorphies) render the applicability of the concept of limited use. The proposal to split the genus Alexandrium on the basis of our current knowledge is rejected herein. The aim here is not to present an alternative analysis and revision, but to maintain Alexandrium. A better constructed and more phylogenetically accurate revision can and should wait until more complete evidence becomes available and there is a strong reason to revise the genus Alexandrium. The reasons are explained in detail by a review of the available molecular and morphological data for species of the genera Alexandrium and Centrodinium. In addition, cyst morphology and chemotaxonomy are discussed, and the need for integrative taxonomy is highlighted.

Plate pattern clarification of the marine dinophyte Heterocapsa triquetra sensu Stein (Dinophyceae) collected at the Kiel Fjord (Germany)

One of the most common marine dinophytes is a species known as Heterocapsa triquetra. When Stein introduced the taxon Heterocapsa, he formally based the type species H. triquetra on the basionym Glenodinium triquetrum. The latter was described by Ehrenberg and is most likely a species of Kryptoperidinium. In addition to that currently unresolved nomenclatural situation, the thecal plate composition of H. triquetra sensu Stein (1883) was controversial in the past. To clarify the debate, we collected material and established the strain UTKG7 from the Baltic Sea off Kiel (Germany, the same locality as Stein had studied), which was investigated using light and electron microscopy, and whose systematic position was inferred using molecular phylogenetics. The small motile cells (18-26 μm in length) had a biconical through fusiform shape and typically were characterized by a short asymmetrically shaped, horn-like protuberance at the antapex. A large spherical nucleus was located in the episome, whereas a single pyrenoid laid in the lower cingular plane. The predominant plate pattern was identified as apical pore complex (Po, cp?, X), 4', 2a, 6'', 6c, 5s, 5''', 2''''. The triradiate body scales were 254-306 nm in diameter, had 6 ridges radiating from a central spine, 9 peripheral and 3 radiating spines, and 12 peripheral bars as well as a central depression in the basal plate. Our work provides a clarification of morphological characters and a new, validly published name for this important but yet formally undescribed species of Heterocapsa: H. steinii sp. nov.

Delimitation of the Thoracosphaeraceae (Dinophyceae), including the calcareous dinoflagellates, based on large amounts of ribosomal RNA sequence data

The phylogenetic relationships of the Dinophyceae (Alveolata) are not sufficiently resolved at present. The Thoracosphaeraceae (Peridiniales) are the only group of the Alveolata that include members with calcareous coccoid stages; this trait is considered apomorphic. Although the coccoid stage apparently is not calcareous, Bysmatrum has been assigned to the Thoracosphaeraceae based on thecal morphology. We tested the monophyly of the Thoracosphaeraceae using large sets of ribosomal RNA sequence data of the Alveolata including the Dinophyceae. Phylogenetic analyses were performed using Maximum Likelihood and Bayesian approaches. The Thoracosphaeraceae were monophyletic, but included also a number of non-calcareous dinophytes (such as Pentapharsodinium and Pfiesteria) and even parasites (such as Duboscquodinium and Tintinnophagus). Bysmatrum had an isolated and uncertain phylogenetic position outside the Thoracosphaeraceae. The phylogenetic relationships among calcareous dinophytes appear complex, and the assumption of the single origin of the potential to produce calcareous structures is challenged. The application of concatenated ribosomal RNA sequence data may prove promising for phylogenetic reconstructions of the Dinophyceae in future.

Bacteria of the Genus Roseobacter Associated with the Toxic Dinoflagellate Prorocentrum lima

The dinoflagellate Prorocentrum lima is known to produce diarrhetic shellfish poisons. However, it is yet unclear if the dinoflagellates themselves or the bacteria associated with them produce the toxins. Here we analyze the toxicity as well as the spectrum of bacteria in two cultures of P. lima, namely P. lima-SY and P. lima-ST, which initially derived from the same P. lima strain PL2V. Toxicity tests, applying the Artemia bioassay revealed in both cultures high levels of toxins. The bacteria, associated with the two cultures, were identified by PCR/nucleotide sequence analysis of the 16S rRNA gene. From cultures of P. lima-SY the dominant sequence was found to share a 93.7% similarity with the sequence of Roseobacter algocolus [R. algicola]; the relative abundance was determined to be 83%. In addition three further sequences of bacteria, grouped to the α-Protobacteria have been identified: Paracoccus denitrificans [90.8%], R. algocolus [94.4%] and Rhizobium huakuii [92.6%]. The identification of bacteria in P. lima-ST revealed that most share highest similarity with Bartonella taylorii but with a relatively low score of 87%. In addition to this sequence, two sequences with high similarity to the genus Roseobacter were obtained. The other sequences identified have not been detected in P. lima-SY. Studies with pure bacterial strains, previously isolated from a culture of P. lima-ST and subsequently cultured on agar plates, revealed that none of them was identical to those identified in the dinoflagellate culture itself. An explanation for the change of the spectrum of bacteria in the different cultures can only be expected when axenic cultures from P. lima are available.