Ultrastructure and phylogeny of Theleodinium calcisporum gen. et sp. nov., a freshwater dinoflagellate that produces calcareous cysts

Abstract

Craveiro S.C., Pandeirada M.S., Daugbjerg N., Moestrup Ø. and Calado A.J. 2013. Ultrastructure and phylogeny of Theleodinium calcisporum gen. et sp. nov., a freshwater dinoflagellate that produces calcareous cysts. Phycologia 52: 488–507. DOI: 10:2216/13–152.1

A freshwater photosynthetic dinoflagellate isolated from a shallow lake near Aveiro, Portugal, was examined by light microscopy, scanning electron microscopy (SEM) and serial-section transmission electron microscopy (TEM), and characterized genetically. Cells were small, spherical to slightly elongated, and had a projecting, nearly cylindrical, apical pore. The chloroplasts were yellowish-brown, arranged near the surface of the cell, and had up to four pyrenoids surrounded by starch sheaths. The cells had a peridinioid plate pattern with Kofoidian plate formula pp, cp, x, 3′ (seldom 4′), 2a, 7′′, 6c, 5s (6s?), 5′′′, 2′′′′. A small extruded peduncle was observed by SEM in cells with intact membranes. A microtubular basket, made of about 46 microtubules disposed in four rows, was seen in the ventral area in connection with the cytoplasmic extension that made the peduncle. The flagellar apparatus was typical of a peridinioid with two roots associated with each of the basal bodies and a layered connective linking the proximal ends of roots 1 and 4. In dense cultures, this organism produced a round resting cyst with a thick wall covered by irregular calcified elements. Energy dispersive X-ray analysis (EDS) analysis of the cysts showed calcium as the most abundant element. A total of 3048 nucleotides of the nuclear ribosomal operon were sequenced and used in a phylogenetic analysis that placed this organism as a sister group to a clade of Scrippsiella species and the parasitic Duboscquodinium collinii. Theleodinium calcisporum gen. et sp. nov. is described for the first freshwater dinoflagellate reported to produce calcareous cysts.

Key Words::

• Calcareous cyst
• Dinophyceae
• ITS
• LSU rDNA
• Microtubular basket
• Phylogeny
• SSU rDNA
• Theleodinium gen. nov.
• Ultrastructure

ACKNOWLEDGEMENTS

SCC was supported by a grant (SFRH/BPD/68537/2010) from the financing program “QREN - POPH - Tipologia 4.1 - Formação Avançada” and by the European Social Funding (FSE) and the Portuguese Ministry of Education and Science (MEC).

SUPPLEMENTARY DATA

Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/13-152.1.s1.