Nioella ostreopsis sp. nov., isolated from toxic dinoflagellate, Ostreopsis lenticularis

A novel short-rod-shaped bacterial strain with poly-β-hydroxybutyric acid granules inside, designated as Z7-4^T, was isolated from a culture of a marine dinoflagellate with palytoxin-producing capacity, Ostreopsis lenticularis OS06, collected from the East China Sea. Cells of Z7-4^T were Gram-stain-negative, non-motile, strictly aerobic, 0.9-1.2 µm wide and 2.0-3.9 µm long. Growth occurred in 1-4 % (w/v) NaCl, at 15-37 °C and at pH 5.0-10.0, with optimum growth in 3.5 % (w/v) NaCl, at 30 °C and at pH 7.0. Analysis of 16S rRNA gene sequence revealed that Z7-4^T shared the highest 16S rRNA gene sequence similarities with Nioella aestuarii JCM 30752^T (98.8 %), followed by Nioella sediminis KCTC 42144^T (98.6 %) and Nioella nitratireducens KCTC 32417^T (96.9 %). Phylogenetic analysis based on nearly complete 16S rRNA gene sequences revealed that Z7-4^T clearly represented a member of the genus Nioella within the family Rhodobacteraceae. The respiratory quinone of Z7-4^T was identified as Q-10. Polar lipids of Z7-4^T were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, three unidentified aminophospholipids and one unidentified phospholipid. The major fatty acids were summed feature 8 (C_18 : 1ω7c and/or C_18 : 1ω6c) and C_16 : 0. The DNA G+C content of Z7-4^T was 63.0 mol%. DNA-DNA hybridization values of the isolate against the closely related type strains were far below the 70 % limit for species delineation. The average nucleotide identity and in silico DNA-DNA genome hybridization relatedness between Z7-4^T and the closely related members of the genus Nioella, N. sediminis KCTC 42144^T and N. nitratireducens KCTC 32417^T, were 91.1 and 46.3 %, and 79.3 and 19.4 %, respectively. On the basis of the results of polyphasic analysis, Z7-4^T is proposed to represent a novel species of the genus Nioella, for which the name Nioella ostreopsis sp. nov. is proposed. The type strain of Nioella ostreopsis is Z7-4^T (=KCTC 62459^T=CCTCC AB 2017231^T).

Ostreopsis lenticularis Y. Fukuyo (Dinophyceae, Gonyaulacales) from French Polynesia (South Pacific Ocean): A revisit of its morphology, molecular phylogeny and toxicity

To date, the genus Ostreopsis comprises eleven described species, of which seven are toxigenic and produce various compounds presenting a major threat to human and environmental health. The taxonomy of several of these species however remains controversial, as it was based mostly on morphological descriptions leading, in some cases, to ambiguous interpretations and even possible misidentifications. The species Ostreopsis lenticularis was first described by Y. Fukuyo from French Polynesia using light microscopy observations, but without genetic information associated. The present study aims at revisiting the morphology, molecular phylogeny and toxicity of O. lenticularis based on the analysis of 47 strains isolated from 4 distinct locales of French Polynesia, namely the Society, Australes, Marquesas and Gambier archipelagos. Observations in light, epifluorescence and field emission scanning electron microscopy of several of these strains analyzed revealed morphological features in perfect agreement with the original description of O. lenticularis. Cells were oval, not undulated, 60.5-94.4 μm in dorso-ventral length, 56.1-78.2 μm in width, and possessed a typical plate pattern with thecal plates showing two sizes of pores. Phylogenetic analyses inferred from the LSU rDNA and ITS-5.8S sequences revealed that the 47 strains correspond to a single genotype, clustering with a strong support with sequences previously ascribed to Ostreopsis sp. 5. Clonal cultures of O. lenticularis were also established and further tested for their toxicity using the neuroblastoma cell-based assay and LCMS/MS analyses. None of the 19 strains tested showed toxic activity on neuroblastoma cells, while LCMS/MS analyses performed on the strains from Tahiti Island (i.e. type locality) confirmed that palytoxin and related structural analogs were below the detection limit. These findings allow to clarify unambiguously the genetic identity of O. lenticularis while confirming previous results from the Western Pacific which indicate that this species shows no toxicity, thus stressing the need to reconsider its current classification within the group of toxic species.

Occurrence of Ostreopsis lenticularis (Dinophyceae: Gonyaulacales) from the Archipiélago de Revillagigedo, Mexican Pacific

From December 2016 to May 2017, 22 phytoplankton surface samples were collected with a 20-μm mesh net at three islands of the Archipiélago de Revillagigedo (Partida, Socorro and San Benedicto), Mexican Pacific. The sites depth was approximately 20-80 m; the surface water temperature was 21-27 °C. The potentially toxic benthic dinoflagellate Ostreopsis lenticularis was present in all the samples. Cells had a lenticular to broadly oval shape, 65-100 μm long and 50-80 μm wide. The taxonomy of the genus Ostreopsis has been unclear due to equivocal ascribing some taxonomic features among species. The identification of specimens from the archipelago was made based on the most important taxonomic characteristics: the thecal plates, the presence of two types of thecal pores (larger and smaller), and the lack of cingulum undulation. The studied cells are compared with O. cf. siamensis, O. labens and O. marina. This is the first record of the species in the archipelago waters.