Diversity of luciferase sequences and bioluminescence production in Baltic Sea <i>Alexandrium ostenfeldii</i>

The toxic dinoflagellate <i>Alexandrium ostenfeldii</i> is the only bioluminescent bloom-forming phytoplankton in coastal waters of the Baltic Sea. We analysed partial luciferase gene (<i>lcf</i>) sequences and bioluminescence production in Baltic <i>A. ostenfeldii</i> bloom populations to assess the distribution and consistency of the trait in the Baltic Sea, and to evaluate applications for early detection of toxic blooms. <i>Lcf</i> was consistently present in 61 Baltic Sea <i>A. ostenfeldii</i> strains isolated from six separate bloom sites. All Baltic Sea strains except one produced bioluminescence. In contrast, the presence of <i>lcf</i> and the ability to produce bioluminescence did vary among strains from other parts of Europe. In phylogenetic analyses, <i>lcf</i> sequences of Baltic Sea strains clustered separately from North Sea strains, but variation between Baltic Sea strains was not sufficient to distinguish between bloom populations. Clustering of the <i>lcf</i> marker was similar to internal transcribed spacer (ITS) sequences with differences being minor and limited to the lowest hierarchical clusters, indicating a similar rate of evolution of the two genes. In relation to monitoring, the consistent presence of <i>lcf</i> and close coupling of <i>lcf</i> with bioluminescence suggests that bioluminescence can be used to reliably monitor toxic bloom-forming <i>A. ostenfeldii</i> in the Baltic Sea.