Chrysochromulina and Prymnesium are important
bloom-forming organisms in marine and brackish waters, respectively. Both
genera
include toxic species, which are primarily implicated in fish kills.
Previous analyses of small subunit (SSU) rDNA sequences from
Chrysochromulina and Prymnesium spp. indicate that
Chrysochromulina is paraphyletic. C. polylepis, which
produced a spectacular, harmful
bloom in 1988, is more closely related to toxic Prymnesium species
than to most other Chrysochromulina species based on rDNA sequence
comparisons. Signatures were identified in the SSU rRNA gene specific for
a clade that comprised primarily toxic taxa (C. polylepis, P.
parvum, P. patelliferum and P. calathiferum)
and that recognized C. polylepis alone.
Oligonucleotide probes complementary to these regions
were designed, and their specificity tested using dot-blot
hybridization on PCR products of the SSU rRNA gene from 28 strains of
Chrysochromulina and Prymnesium. Whole-cell
hybridizations were performed with FLUOS- as well as Cy3-labelled probes
on cultured
species from both genera, and were detected with both epifluorescence
microscopy and flow cytometry. The probes afforded easy
identification of clonal isolates of C. polylepis and a
cluster of closely related species including C. polylepis and
Prymnesium spp. The
feasibility of using these probes for species identification and
studies of population dynamics in the field is discussed.