| Summary: | The dinoflagellate <i>Alexandrium minutum</i> (<i>A. minutum</i>) which can produce paralytic shellfish toxins (PSTs) is often used as a model to study the migration, biotransformation, accumulation, and removal of PSTs. However, the mechanism is still unclear. To provide a new tool for related studies, we tried to label PSTs metabolically with <sup>15</sup>N stable isotope to obtain <sup>15</sup>N-PSTs instead of original <sup>14</sup>N, which could be treated as biomarker on PSTs metabolism. We then cultured the <i>A. minutum</i> AGY-H46 which produces toxins GTX1-4 in f/2 medium of different <sup>15</sup>N/P concentrations. The <sup>15</sup>N-PSTs’ toxicity and toxin profile were detected. Meanwhile, the <sup>15</sup>N labeling abundance and <sup>15</sup>N atom number of <sup>15</sup>N-PSTs were identified. The <sup>14</sup>N of PSTs produced by <i>A. minutum</i> can be successfully replaced by <sup>15</sup>N, and the f/2 medium of standard <sup>15</sup>N/P concentration was the best choice in terms of the species’ growth, PST profile, <sup>15</sup>N labeling result and experiment cost. After many (>15) generations, the <sup>15</sup>N abundance in PSTs extract reached 82.36%, and the <sup>15</sup>N atom number introduced into GTX1-4 might be 4–6. This paper innovatively provided the initial evidence that <sup>15</sup>N isotope application of labeling PSTs in <i>A. minutum</i> is feasible. The <sup>15</sup>N-PSTs as biomarker can be applied and provide further information on PSTs metabolism.
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