Toxin Dynamics and Genomic Diversity in Pyrodinium bahamense Populations from the Indian River Lagoon, Florida

Pyrodinium bahamense is a saxitoxin-producing bioluminescent dinoflagellate that forms annual recurring blooms in the Indian River Lagoon (IRL), FL. Little information exists as to the extent of bloom toxicity. This study examined toxin dynamics in P. bahamense IRL field populations from two sites in the northern IRL (NIRL). Additionally, genomic diversity and transcription were assessed using quantitative molecular assays targeting key functional genes in P. bahamense ecology: sxtA4 (toxin biosynthesis), rbcL (photosynthesis), and lcf (bioluminescence). A positive correlation was found between sxtA4 transcript copy number and toxicity, mirroring the trend recorded in previous seasons and indicating that sxtA4 transcripts can serve as a molecular proxy for bloom toxicity. Lab experiments with 32 strains isolated from the NIRL showed a large variation in copy number for both sxtA4 (42–318 copies cell−1, dependent on strain) and rbcL (1385 to 4911 copies cell−1). An lcf qPCR assay developed here showed substantial variation among isolates as well. These results are indicative of the underlying diversity in field populations, as genome copy number variation is a major driver of genome evolution and diversity. A negative correlation was found between cell abundance and toxin quota in field populations. Growth and toxin quota were also found to have a negative correlation in the 32 isolates. Based on these collective lab and field results, a model is presented in which P. bahamense populations utilize both their toxicity and bioluminescence in bloom development and persistence.