Physiological changes and gene expression in the mixotrophic haptophyte, Prymnesium parvum, respond to mixed nitrogen sources

Prymnesium parvum is a toxin-producing haptophyte that adapts to various conditions in aquaculture wastewater, using strategies like allelopathy, toxicity, and predation to survive. However, knowledge about physiological and genetic responses of P. parvum to mixed nitrogen sources in aquaculture wastewater is still limited. Here, we cultured P. parvum in simulated aquaculture wastewater nitrogen composition, and revealed physiological and gene expression responses of P. parvum to mixed nitrogen sources. Under high concentrations mixed nitrogen sources (8.83 × 10³ μmol/L), P. parvum shows strong adaptability and competitiveness, predisposing it to harmful algal blooms (HABs) outbreaks. At low concentrations 8.83 × 10¹ μmol/L), it compensates by consuming other algae and producing toxins for defense. Transcriptomic data indicate that P. parvum upregulates nitrogen-related genes when transitioning from nitrate to mixed nitrogen, and downregulates them with increasing concentrations, significantly impacting glutamate metabolism and potentially enhancing direct ammonia conversion to L-glutamate, bypassing L-glutamine. Metabolic reprogramming in P. parvum may drive cell proliferation and HABs formation, with ecological consequences for aquaculture nitrogen dynamics.