Benico, GarryAzanza, Rhodora2025-06-122022-04-01Benico, G., & Azanza, R. (2022). Characterization of <i>Alexandrium tamutum</i> (Dinophyceae) isolated from Philippine waters, with the rare detection of paralytic shellfish toxin. <i>Philippine Journal of Systematic Biology</i>, <i>15</i>(1), 1-13.10.26757/pjsb2021a15009https://hdl.handle.net/20.500.14697/559We acknowledge the Department of Science and Technology Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (DOST PCAARRD) and the University of the Philippines-The Marine Science Institute (UP-MSI) for the funding support. We are grateful for the assistance of Joshua Vacarizas, Keith Pinto and Jenelyn Mendoza for the molecular and toxicity analyses of the cultures. We also acknowledge Estrelita Flores, Emelita Eugenio and Jayson Orpeza for their assistance during the fieldwork and other logistical support.<i>Alexandrium tamutum</i> M.Montressor, A.Beran & U.John is a non-toxic, bloom-forming dinoflagellate species commonly reported in temperate waters. In this study, 8 cultures of <i>A. tamutum</i> established from Bolinao Channel and Manila Bay, Philippines were characterized in terms of their morphology, phylogeny and toxicity. Cells were roundish, measuring 25.5 –29.84 µm long and 26.2–28.45 µm wide. The nucleus is equatorially elongated and located at the center of the cell. The chloroplasts are numerous, golden brown in color and radially arranged. Thecal tabulation is typical of <i>Alexandrium</i>: APC, 4', 6'', 6c, 6s, 5''', 2''''. Shape of the taxonomically informative thecal plates such as sixth precingular plate (6'') and posterior sulcal plate (sp) was similar to <i>A. tamutum</i>, which confirms the species identity. However, the presence of anterior and posterior attachment pores observed in our cultured isolates is the first case in this species. Molecular phylogeny inferred from LSU rDNA and ITS supports our identification by forming a well-supported clade composed of <i>A. tamutum</i> strains from other geographic regions. HPLC analysis showed that <i>A. tamutum</i> is generally non-toxic except for strain ATC9 which has low amount of decarbamoylsaxitoxin (dcSTX), resulting to a toxicity of 0.07 fmole STX eq per cell. The present study reports the first verified occurrence of Philippine <i>A. tamutum</i> with reliable morphological and molecular information, including the first record in Manila Bay and first detection of PST in one strain at a certain culture period.enDinoflagellatesParalytic shellfish poisoningSaxitoxinPhylogenyNucleotide sequenceArticleSDG 14 - Life below waterSDG 3 - Good health and well-beingSDG 12 - Responsible consumption and productionDinophyceaeparalytic shellfish poisoningtoxinsmorphologyphylogenytoxicityDNA sequencesphylogenetic analysistoxicity testsChallenge 1: Understand and beat marine pollutionChallenge 6: Increase community resilience to ocean hazards