Light spectra shape population structure and the allocation of fucoxanthin and fatty acids with secondary phytohormone modulation in Tisochrysis lutea

초록

Fucoxanthin and long-chain omega-3 fatty acids, particularly docosahexaenoic acid, are valuable microalgal products for nutraceutical and aquaculture applications. We investigated how light spectrum and phytohormone treatment affected growth, photosynthetic traits, population structure, and metabolite allocation in Tisochrysis lutea KCTC AG61399. Cultures were grown under white, red, or blue light-emitting diodes and four phytohormone regimes (control, abscisic acid, gibberellic acid, and indole-3-acetic acid) under continuous light at 100 mu mol photons m-2 s-1. Growth, chlorophyll a, Fv/Fm, fucoxanthin, total fatty acids, fatty acid composition, and image-based single-cell cytometry profiles were quantified. Light spectrum was the dominant factor structuring the response. By day 8, red light produced the highest cell density (9.21 & times; 106 cells mL-1) and endpoint cell productivity, approximately 1.5-fold and 1.4-fold higher than under white and blue light, respectively. Red light also yielded the highest fucoxanthin content (1.43-1.62% DW), total fatty acid content (maximum 14.60% DW), and strongly single-cell-dominant populations (96.72-98.46%) with minimal aggregation. Auxiliary morphometric analysis showed that red-light cultures converged toward a smaller-cell, lower-biovolume single-cell state, whereas white and blue light retained larger dividing and aggregated fractions. Fatty acid class composition shifted with light spectrum, indicating altered lipid allocation and omega-3 partitioning rather than uniform expansion of the fatty acid pool. Phytohormones modified selected endpoints within each spectral regime but did not override the spectrum-driven pattern. These results show that biochemical measurements combined with event-based phenotyping improve interpretation of cultivation responses and support condition screening for coordinated fucoxanthin and fatty acid production in T. lutea.

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