Genetics and morphology characterize the dinoflagellate Symbiodinium voratum, n. sp., (Dinophyceae) as the sole representative of Symbiodinium Clade E.
Dinoflagellates in the genus Symbiodinium are ubiquitous in shallow marine habitats where they commonly exist in symbiosis with cnidarians. Attempts to culture them often retrieve isolates that may not be symbiotic, but instead exist as free-living species. In particular, cultures of Symbiodinium clade E obtained from temperate environments were recently shown to feed phagotrophically on bacteria and microalgae. Genetic, behavioral, and morphological evidence indicate that strains of clade E obtained from the northwestern, southwestern, and northeastern temperate Pacific Ocean as well as the Mediterranean Sea constitute a single species: Symbiodinium voratum n. sp. Chloroplast ribosomal 23S and mitochondrial cytochrome b nucleotide sequences were the same for all isolates. The D1/D2 domains of nuclear ribosomal DNA were identical among Western Pacific strains, but single nucleotide substitutions differentiated isolates from California (USA) and Spain. Phylogenetic analyses demonstrated that S. voratum is well-separated evolutionarily from other Symbiodinium spp. The motile, or mastigote, cells from different cultures were morphologically similar when observed using light, scanning, and transmission electron microscopy; and the first complete Kofoidian plate formula for a Symbiodinium sp. was characterized. As the largest of known Symbiodinium spp., the average coccoid cell diameters measured among cultured isolates ranged between 12.2 (± 0.2 SE) and 13.3 (± 0.2 SE) μm. Unique among species in the genus, a high proportion (approximately 10-20%) of cells remain motile in culture during the dark cycle. Although S. voratum occurs on surfaces of various substrates and is potentially common in the plankton of coastal areas, it may be incapable of forming stable mutualistic symbioses.
School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Korea.
Hae Jin
HJ
Jeong
Sung Yeon
SY
Lee
Nam Seon
NS
Kang
Yeong Du
YD
Yoo
An Suk
AS
Lim
Moo Joon
MJ
Lee
Hyung Seop
HS
Kim
Wonho
W
Yih
Hiroshi
H
Yamashita
Todd C
TC
LaJeunesse
D056893:Alveolata / Q000145:classification* / Q000166:cytology / Q000235:genetics / Q000302:isolation & purification; D000818:Animals; D002140:California; D016000:Cluster Analysis; D045303:Cytochromes b / Q000235:genetics; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D020459:Genes, rRNA; D008522:Mediterranean Sea; D008853:Microscopy; D008969:Molecular Sequence Data; D015388:Organelles / Q000648:ultrastructure; D010140:Pacific Ocean; D010802:Phylogeny; D016053:RNA, Protozoan / Q000235:genetics; D012338:RNA, Ribosomal, 23S; D012623:Seawater / Q000469:parasitology; D017422:Sequence Analysis, DNA; D013030:Spain
D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D016053:RNA, Protozoan; D012338:RNA, Ribosomal, 23S; D045303:Cytochromes b
phylogeny; plastid genes; species; systematics; taxonomy