Effects of light quality and intensity on growth and bromoform content of the red seaweed Asparagopsis taxiformis

Species of the genus Asparagopsis are rich in halogenated bioactive compounds, particularly bromoform. Its use as a feed additive in ruminant livestock drastically decreases the animal’s methane production, thereby reducing the industry’s environmental impact. Addressing the high demand for Asparagopsis biomass requires the understanding of the culture conditions that promote higher growth rates and bromoform content. Here we evaluated how different light quality combinations (High-Blue:Red, Medium Blue:Red, High-Blue:Green:Red, and White) and four light intensities (30, 60, 90 and 120 μmol photons m −2 s −1 ) affect the growth and bromoform content of the Asparagopsis taxiformis tetrasporophyte in indoor tumbling cultures at two biomass densities. We also assessed the effect of light intensity on the photosynthetic response by measuring oxygen evolution rates. Light spectra containing intermediate wavelengths promoted higher growth, regardless of biomass density. Of the different light qualities tested, white light promoted the highest bromoform content. Increasing light intensity led to a positive response in A. taxiformis growth. However, the photosynthetic parameters estimated showed that the two higher light intensity treatments were above the saturation irradiance, for both culture densities. This, along with the observed development of contamination, suggests that long-term cultures of A. taxiformis should be maintained at light intensities no higher than 60 μmol photons m −2 s −1 . In addition, we found that exposing cultures to higher irradiances does not guarantee a bromoform-richer biomass. These results offer valuable insights for optimizing biomass and bioactive compound production in indoor cultures of the Asparagopsis genus.