Publication Date:
2020-09-30
Description:
The cosmopolitan, potentially toxic dinoflagellate Protoceratium reticulatum possesses a fossilizable cyst stage
which is an important paleoenvironmental indicator. Slight differences in the internal transcribed spacer ribosomal
DNA (ITS rDNA) sequences of P. reticulatum have been reported, and both the motile stage and cyst
morphology of P. reticulatum display phenotypic plasticity, but how these morpho-molecular variations are related
with ecophysiological preferences is unknown. Here, 55 single cysts or cells were isolated from localities in
the Northern (Arctic to subtropics) and Southern Hemispheres (Chile and New Zealand), and in total 34 strains
were established. Cysts and/or cells were examined with light microscopy and/or scanning electron microscopy.
Large subunit ribosomal DNA (LSU rDNA) and/or ITS rDNA sequences were obtained for all strains/isolates. All
strains/isolates of P. reticulatum shared identical LSU sequences except for one strain from the Mediterranean Sea
that differs in one position, however ITS rDNA sequences displayed differences at eight positions. Molecular
phylogeny was inferred using maximum likelihood and Bayesian inference based on ITS rDNA sequences. The
results showed that P. reticulatum comprises at least three ribotypes (designated as A, B, and C). Ribotype A
included strains from the Arctic and temperate areas, ribotype B included strains from temperate regions only,
and ribotype C included strains from the subtropical and temperate areas. The average ratios of process length to
cyst diameter of P. reticulatum ranged from 15% in ribotype A, 22% in ribotype B and 17% in ribotype C but cyst
size could overlap. Theca morphology was indistinguishable among ribotypes. The ITS-2 secondary structures of
ribotype A displayed one CBC (compensatory change on two sides of a helix pairing) compared to ribotypes B
and C. Growth response of one strain from each ribotype to various temperatures was examined. The strains of
ribotypes A, B and C exhibited optimum growth at 15 °C, 20 °C and 20–25 °C, respectively, thus corresponding to
cold, moderate and warm ecotypes. The profiles of yessotoxins (YTXs) were examined for 25 strains using liquid
chromatography coupled with tandem mass spectrometry (LC–MS/MS). The parent compound yessotoxin (YTX)
was produced by strains of ribotypes A and B, but not by ribotype C strains, which only produced the structural
variant homoyessotoxin (homoYTX). Our results support the notion that there is significant intra-specific
variability in Protoceratium reticulatum and the biogeography of the different ribotypes is consistent with specific
ecological preferences.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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