Microbial nano-selenium biotransformation modulates growth and toxin homeostasis in PST-producing dinoflagellates
Harmful algal blooms caused by paralytic shellfish toxin (PST)-producing dinoflagellates represent a major ecological and public-health concern. Recent evidence indicates that phycosphere bacteria can biotransform inorganic selenium into bioavailable nano-selenium (SeNPs), yet the effects of this microbial process on dinoflagellate physiology remain largely unknown. In this study, we performed RNA-seq analyses on three PST-producing species—Alexandrium pacificum, A. catenella, and Centrodinium punctatum—to examine transcriptional responses to bacterially synthesized SeNPs.  Exposure to nano-selenium markedly enhanced growth rates and prolonged the exponential growth phase across all three species, suggesting a strong antioxidant and growth-stabilizing effect. Moreover, SeNP-treated cultures maintained relatively stable PST toxin profiles throughout 30 days, whereas control groups exhibited clear shifts in toxin composition over time. These results indicate that nano-selenium contributes to both high-density bloom maintenance and toxin homeostasis in harmful dinoflagellates.  This dataset provides a mechanistic framework for understanding how nutrient-driven bacterial selenium bioconversion may influence bloom dynamics, host cellular processes, and toxin regulation. The RNA-seq data generated here support future investigations into host–microbe–elemental cycling interactions that shape harmful algal bloom formation.