Elsevier

Protist

Volume 170, Issue 5, November 2019, 125680
Protist

Original Paper
Gertia stigmatica gen. et sp. nov. (Kareniaceae, Dinophyceae), a New Marine Unarmored Dinoflagellate Possessing the Peridinin-type Chloroplast with an Eyespot

https://doi.org/10.1016/j.protis.2019.125680Get rights and content

Marine unarmored dinoflagellates in the family Kareniaceae are known to possess chloroplasts of haptophyte origin, which contain fucoxanthin and its derivatives as major carotenoids, and lack peridinin. In the present study, the first species with the peridinin-type chloroplast in this family, Gertia stigmatica gen. et sp. nov., is described on the basis of ultrastructure, photosynthetic pigment composition, and molecular phylogeny inferred from nucleus- and chloroplast-encoded genes. Cells of G. stigmatica were small and harboring a chloroplast with an eyespot and two pyrenoids. The apical structure complex was straight, similar to Karenia and Karlodinium. Under transmission electron microscopy, the chloroplast was surrounded by two membranes, and the eyespot was composed of a single layer of osmiophilic globules (eyespot type A); this was never previously reported from the Kareniaceae. High performance liquid chromatography demonstrated the chloroplast contains peridinin, and neither fucoxanthin nor 19′-acyloxyfucoxanthins was identified. A phylogeny based on nucleus-encoded rDNAs suggested a position of G. stigmatica in the Kareniaceae, but not clustered within the previously described genera, i.e., Karenia, Karlodinium and Takayama. A phylogeny of chloroplast-encoded psbA, psbC and psbD indicated the chloroplast is of peridinin-type typical of dinoflagellates, but the most related species remains unclear.

Introduction

The family Kareniaceae is mainly comprised of three unarmored dinoflagellate genera, Karenia, Karlodinium and Takayama (Bergholtz et al., 2005, Daugbjerg et al., 2000, de Salas et al., 2008). One of characteristic features of this family is the shape of the furrow-like apical structure complex (ASC, = apical groove). Daugbjerg et al. (2000) described two genera with the straight ASC, Karenia and Karlodinium, the latter having a ventral pore and plug-like structure. De Salas et al. (2003) subsequently established the genus Takayama with a sigmoid ASC, showing a close relationship to Karlodinium. Recently, the affinity of Asterodinium gracile Sournia and Brachidinium capitatum F. J. R. Taylor to the Kareniaceae was demonstrated by molecular phylogeny, justifying the previous morphological observation of these species having a straight ASC (Benico et al. 2019; Gómez et al. 2005; Gómez 2006; Henrichs et al. 2011). Gómez et al. (2016) provided SSU rDNA sequence of Ptychodiscus noctiluca Stein, which similarly possesses a straight ASC, but its phylogenetic relationship to the Kareniaceae was not fully resolved. Members of the Kareniaceae, especially the three major genera, are recognized as fish-killing dinoflagellates (e.g., Dai et al., 2014, Leong et al., 2015, Lim et al., 2014, Onoue et al., 1985, Takayama, 1981, Takayama, 1985, Takayama and Matsuoka, 1991, Takayama et al., 1998, Yang et al., 2000), and more than 30 species have so far been described (e.g., Bergholtz et al., 2005, Daugbjerg et al., 2000, de Salas et al., 2003, de Salas et al., 2004, de Salas et al., 2005, de Salas et al., 2008, Gu et al., 2013, Haywood et al., 2004, Luo et al., 2018, Nézan et al., 2014, Yang et al., 2000, Yang et al., 2001).

Another diagnostic feature of the Kareniaceae is the possession of chloroplasts (i.e., photosynthetic plastids) containing fucoxanthin and 19′-acyloxyfucoxanthins (i.e., 19′-hexanoyloxyfucoxanthin and 19′-butanoyloxyfucoxanthin; 19′-AF-type) and lacking peridinin (e.g., Bergholtz et al., 2005, Bjørnland and Tangen, 1979, Chang and Gall, 2013, de Salas et al., 2003, de Salas et al., 2004, de Salas et al., 2005, Hansen et al., 2000, Tangen and Bjørnland, 1981), which is different from the peridinin-type chloroplast typical in dinoflagellates. Phylogeny of plastid-encoded DNAs showed the kareniacean chloroplast to be of haptophyte origin (e.g., Gabrielsen et al., 2011, Ishida and Green, 2002, Takishita et al., 1999, Takishita et al., 2000, Takishita et al., 2004, Takishita et al., 2005, Tengs et al., 2000, Waller and Koreny, 2017).

A naked dinoflagellate recently reported from the Ross Sea, Antarctic Ocean, does not have the typical chloroplast, even though it is closely related to the Kareniaceae in molecular analysis (Gast et al. 2006). According to Gast et al. (2007), this dinoflagellate possesses temporary chloroplasts (kleptochloroplasts) captured from the haptophyte Phaeocystis sp.; however, the phylogenetic position of this kleptochloroplast is not closely related to the permanent chloroplasts of Karenia and Karlodinium in the haptophyte clade. Similar isolates related to the Ross Sea dinoflagellate were also reported from the French coast (as Kareniaceae sp. in Nézan et al. 2014). These isolates are referred to as ‘kleptoplastic sp.’ in this article.

An interesting novel kareniacean species was isolated from the Japanese coast. This small marine dinoflagellate has the straight ASC of the Kareniaceae, but differs in having the peridinin-type chloroplast with an eyespot. In the present study, Gertia stigmatica gen. et sp. nov. is proposed for this isolate, with the description of its ultrastructure and pigment composition, and discussion of the evolutionary status on the basis of molecular phylogeny inferred from nucleus- and chloroplast-encoded DNAs.

Section snippets

Gertia K. Takahashi et Iwataki gen. nov.

Unarmored dinoflagellates with chloroplast containing peridinin as a major pigment. Straight furrowed apical structure complex present.
Type species: Gertia stigmatica (described below).
Etymology: Named after Dr. Gert Hansen who proposed the genus Karenia Hansen et Moestrup ex Daugbjerg et al. (2000).

Gertia stigmatica K. Takahashi et Iwataki sp. nov.

Marine unarmored dinoflagellate. Cells ellipsoid, 5.9–9.5 μm long and 4.9–7.8 μm wide, with the epicone smaller than the hypocone. Cingulum anterior, displaced about one and a half cingulum width.

Taxonomy

Gertia stigmatica possesses the straight ASC, the character shared with Karenia and Karlodinium, and its position in the Kareniaceae was supported by nucleus-encoded rDNA phylogenies. On the other hand, the chloroplast found in G. stigmatica was of peridinin-type, which is distinct from 19′-AF-type reported in other kareniacean species (Benico et al., 2019, Daugbjerg et al., 2000, de Salas et al., 2003). This pigment composition does not correspond with the diagnosis of the family Kareniaceae

Methods

Culture: A strain of Gertia stigmatica gen. et sp. nov. (mdd472-kt strain) originated from a surface seawater off the coast of Manazuru, Sagami Bay, Japan (35°09′N, 139°10′E) in October 2016. Heterocapsa circularisquama and Karenia mikimotoi cultures used in pigment analyses were collected from Mikawa Bay, Japan in 2018, and from Manila Bay, Philippines in 2018, respectively. 500 mL of surface water obtained was prescreened by using a 20 μm mesh, and gently concentrated by gravity filtration

Acknowledgements

We appreciate Dr. Shinji Shimode of Yokohama National University and Ms. Shiori Otake of University of Tokyo for their sampling assistance. Dr. Kazutaka Takahashi of University of Tokyo provided experimental tools including maintenance of culture strain, molecular analysis and EM preparation. Dr. Fumiko Ishizuna of University of Tokyo provided assistance on TEM. Dr. Tomoyo Katayama and Mr. Shota Takino of University of Tokyo and Dr. Takashi Yoshikawa of Tokai University provided assistance on

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