Effects of light quality and nutrient availability on accumulation of mycosporine-like amino acids in Gymnodinium catenatum (Dinophycea)

•Gymnodinium catenatum (Dinophycea) was studied for UV photoprotective pigments.•High culture absorption was observed in both the near- and far-UVA range.•Shinorine and porphyra-334 were the most abundant MAAs in the far-UVA.•The unknown M-370 was the most abundant compound in the near-UVA.•Compounds absorbing in the far- and near-UVA range can be regulated separately.

A Portuguese Gymnodinium catenatum Graham strain was studied for its ultraviolet (UV) photoprotective pigments. This strain presented high absorption in the UVA region, in particular in the near UVA region around 370 nm, followed by the far-UVA region around 340 nm. Absorption in the near-UVA increased when grown under fluorescent when compared to halogen light. This was even more relevant when grown under nutrient-limiting conditions, which even surpassed absorption in the blue region, closely resembling absorption in natural plankton assemblages reported in the literature. HPLC analysis for mycosporine-like amino acids (MAAs), revealed several UV photoprotective pigments common in other marine microalgae from the northwest Atlantic. Amongst the compounds absorbing in the far-UVA region, three were identified by spectra and retention time characteristics: shinorine, porphyra-334, and mycosporine-glycine. In the near-UVA region, the unknown M-370 was usually the most abundant, followed by palythene. The proportional and absolute cellular concentrations of MAAs absorbing in the near-UVA region increased with fluorescent light when compared to halogen light. Additional experiments with light filtration suggest the set of MAAs absorbing in the near-UVA region seem to be regulated separately from the other set of MAAs absorbing in the far-UVA region, and those from the near-UVA region might be stimulated not only by UV but by blue light also. Nutrient availability affected profile: a shift towards MAAs with low nitrogen:carbon ratio (e.g.: mycosporine-glycine) was observed. As G. catenatum requires extensive UV-photoprotection over the entire UVA range, nitrogen availability might strongly restrict blooming, as MAAs are nitrogen-based. This UV sensitivity might help explaining its pronounced autumnal seasonality, tied to a reduced solar exposure.

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