Morphological Variation and Phylogenetic Analysis of the Dinoflagellate Gymnodinium aureolum from a Tributary of Chesapeake Bay

Abstract

Cultures of four strains of the dinoflagellate Gymnodinium aureolum (Hulburt) G. Hansen were established from the Elizabeth River, a tidal tributary of the Chesapeake Bay, USA. Light microscopy, scanning electron microscopy, nuclear-encoded large sub-unit rDNA sequencing, and culturing observations were conducted to further characterize this species. Observations of morphology included: a multiple structured apical groove; a peduncle located between the emerging points of the two flagella; pentagonal and hexagonal vesicles on the amphiesma; production and germination of resting cysts; variation in the location of the nucleus within the center of the cell; a longitudinal ventral concavity; and considerable variation in cell width/length and overall cell size. A fish bioassay using juvenile sheepshead minnows detected no ichthyotoxicity from any of the strains over a 48-h period. Molecular analysis confirmed the dinoflagellate was conspecific with G. aureolum strains from around the world, and formed a cluster along with several other Gymnodinium species. Morphological evidence suggests that further research is necessary to examine the relationship between G. aureolum and a possibly closely related species Gymnodinium maguelonnense.

Ecology of Gymnodinium aureolum. I. Feeding in western Korean waters

“…The morphology of this Korean strain of G. aureolum was very similar to that of G. aureolum described by Hansen et al (2000), Daugbjerg et al (2000), and Tang et al (2008). Cell length and width of live cells of this Korean strain growing photosynthetically (18.0 to 28.4 and 11.6 to 21.2 μm, respectively) were similar to the ranges of the strains isolated from a tributary of Chesapeake Bay, Pettaquamscutt River, and small embayments in the Woods Hole area in Massachusetts, USA (14 to 47 and 11 to 43 μm; summarized by Tang et al 2008).…”

“…The morphology of this Korean strain of G. aureolum was very similar to that of G. aureolum described by Hansen et al (2000), Daugbjerg et al (2000), and Tang et al (2008). Cell length and width of live cells of this Korean strain growing photosynthetically (18.0 to 28.4 and 11.6 to 21.2 μm, respectively) were similar to the ranges of the strains isolated from a tributary of Chesapeake Bay, Pettaquamscutt River, and small embayments in the Woods Hole area in Massachusetts, USA (14 to 47 and 11 to 43 μm; summarized by Tang et al 2008). In addition, the sequences of rDNA of this Korean strain were the same or very similar to those of strains of G. aureolum isolated from a tributary of Chesapeake Bay, USA (Tang et al 2008); the Pettaquamscutt River, USA ; the Benguela Current waters off Namibia; and the waters off Denmark , Australia (de Salas et al 2003), andNew Zealand (de Salas et al 2005).…”

“…Cell length and width of live cells of this Korean strain growing photosynthetically (18.0 to 28.4 and 11.6 to 21.2 μm, respectively) were similar to the ranges of the strains isolated from a tributary of Chesapeake Bay, Pettaquamscutt River, and small embayments in the Woods Hole area in Massachusetts, USA (14 to 47 and 11 to 43 μm; summarized by Tang et al 2008). In addition, the sequences of rDNA of this Korean strain were the same or very similar to those of strains of G. aureolum isolated from a tributary of Chesapeake Bay, USA (Tang et al 2008); the Pettaquamscutt River, USA ; the Benguela Current waters off Namibia; and the waters off Denmark , Australia (de Salas et al 2003), andNew Zealand (de Salas et al 2005). Therefore, this Korean strain of G. aureolum was confirmed to be conspecific with strains isolated from the waters of other countries, indicating that G. aureolum has a worldwide distribution with very low variation in rDNA sequence (1 to 5 bp difference).…”

“…During a 2008 red tide event on the west coast of Korea, we isolated and established a clonal culture of a dinoflagellate that morphological and genetic analysis revealed to be Gymnodinium aureolum (Hulburt 1957, Tang et al 2008. Thus in the present study we report the morphological and genetic characteristics of this strain by generating phylogenetic trees on the basis of the sequences of LSU rDNA.…”

“…However, it is difficult to determine whether Gyrodinium aureolum isolates reported by researchers before Hansen et al (2000) and Daugbjerg et al (2000) were Gymnodinium aureolum or K. mikimotoi. An increasing number of taxonomic studies have been conducted on Gymnodinium aureolum strains isolated after the year 2000 (de Salas et al 2003, Bergholtz et al 2006, Tang et al 2008.…”