Pyrodinium bahamense is a saxitoxin (STX)-producing bioluminescent dinoflagellate that blooms in the Indian River Lagoon (IRL), Florida, the bioluminescent bays in Puerto Rico, and the Indo-Pacific. STX is a potent neurotoxin that binds with high affinity to the voltage-gated sodium channel in humans and causes Paralytic Shellfish Poisoning. Its role in the ecology of P. bahamense remains unknown. While P. bahamense previously existed in Florida with no known record of toxicity, toxic blooms have emerged in the IRL over the past 20 years. The core STX biosynthetic pathway genes have been identified. SxtA4 is essential for toxin synthesis and so serves as a molecular proxy for toxicity. Our lab developed a single-cell multiplex PCR assay targeting the 18S rRNA and sxtA4 genes in P. bahamense and found that some cells within the same sub-populations lack sxtA4. In this work, we examine these genotype dynamics in relation to cell abundance and toxicity in spatially and temporally separate populations in the IRL. Our toxin data, normalized as toxin quota per cell, show that toxin content changes substantially both (1) temporally within the same sub-populations and (2) among sub-populations. Assimilating the collective data among sites revealed a significant negative correlation (Spearman Correlation, -0.434; p = 0.02) between toxin quota per cell and cell abundance: toxin quota decreased with increased cell abundance. The potential ecological link between toxicity and bioluminescence is discussed based on these findings.
Cusick et al. (Fri,) studied this question.