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The dinoflagellate Amphidinium carterae produces valuable fatty acids, pigments, and bioactive polyketides (e.g., amphidinols). Despite recent advances in its intensive cultivation, challenges remain that justify further work. This study explored the effects of phytohormone supplementation on growth and metabolism using a One Strain Many Compounds (OSMAC) approach. Auxins, cytokinins, jasmonates, amines, abscisic acid, gibberellic acid, and other signaling molecules were screened in batch cultures. Synthetic auxin 2-naphthoxyacetic acid (BNOA) at a final concentration of 14.84 μM (3 mg·L−1) emerged as the most stimulant. On a small scale, BNOA increased biomass productivity by up to 32 % and hemolytic activity in terms of productivity by 50 %. Scaling up in 10 L bubble column photobioreactor cultures with the addition of BNOA, but without CO 2 supplementation, resulted in levels of amphidinol production comparable to those achieved with CO 2 addition. Compared to the control without BNOA, BNOA cultures generated 2.2-fold more biomass during the stationary growth phase, and amphidinol production increased fourfold per unit of biomass. This work reveals that the addition of exogenous phytohormones such as BNOA can sustain the production of valuable metabolites in A. carterae, eliminating the need for additional CO 2 and its associated costs. This promising approach highlights the potential of hormone supplementation as a cost-effective and efficient cultivation strategy for dinoflagellate bioprocesses. • 12 hormones from 8 different groups were evaluated. • 2-Naphthoxyacetic acid (BNOA) the most potent growth enhancer. • Scaled up cultures with BNOA without CO 2 addition maintained amphidinol production levels. • Scaled up cultures with BNOA without CO 2 addition generated 2.2-fold more biomass. • First time addition of exogenous phytohormones sustains the production of the valuable metabolites in A. carterae cultures. [ABSTRACT FROM AUTHOR]

The dinoflagellate Amphidinium carterae is a promising source of unique bioactive compounds with potential applications in diverse industries. Abiotic strategies for increasing bioactive cell quota have been preferred for cost-effectiveness, controllability, and existing knowledge. The supernatants of Heterosigma akashiwo and Pavlova sp. enhanced haemolytic activity of A. carterae by 2.3 times and improved its final biomass by 10 % when added to the growth medium. Prymnesium parvum supernatant increased the total lipid content of A. carterae by 50 %, while Pleurochrysis roscoffensis supernatant boosted its total carotenoid content by 40 %. This study demonstrated a rapid screening strategy for evaluating growth responses and highlights the potential of using allelopathic strategies to enhance bioactive metabolite production. Utilizing supernatants for the formulation of growth media fosters a circular economy by repurposing resources, minimizing waste, and promoting sustainability in the microalgal biotechnological industry. [Display omitted] • 38 microalgal supernatants were evaluated for stimulating A. carterae. • Quorum sensing allowed increasing total lipid and carotenoid content. • Evidence of amphidinols overproduction was found for many species. • Repurposing supernatants as a biostimulant enhances circularity. [ABSTRACT FROM AUTHOR]

Cells of five unarmoured kleptoplastidic dinoflagellates, Amphidinium latum , Amphidinium poecilochroum , Gymnodinium amphidinioides, Gymnodinium acidotum and Gymnodinium aeruginosum were observed under light and/or scanning electron microscopy and subjected to single-cell PCR. The SSU rDNA and the partial LSU rDNA of all the examined species were sequenced, and the SSU rDNA of G. myriopyrenoides was sequenced. Phylogenetic analyses revealed that the unarmoured kleptoplastidic species formed a monophyletic clade within the Gymnodinium -clade sensu Daugbjerg et al. (2000) . The sister taxa for this clade were Gymnodinium palustre and Spiniferodinium galeiforme , both of which possess brown-coloured chloroplasts. The results indicated that acquisition of kleptoplastidy in these unarmoured dinoflagellates was a single event and that these unarmoured kleptoplastidic dinoflagellates may have evolved from a form with permanent chloroplasts. Molecular trees suggested that the acquisition of kleptoplastidy took place in a marine habitat and later some species colonized the freshwater habitat. Because these unarmoured kleptoplastidic dinoflagellates are monophyletic and characterized by distinct morphological and cytological features (including the presence of the same type of apical groove, absence of nuclear chambers in the nuclear envelope, absence of genuine chloroplasts, and the possession of kleptochloroplasts), we propose the establishment of a new genus, Nusuttodinium , to accommodate all these dinoflagellates. [ABSTRACT FROM AUTHOR]