+UVA treatment increases the degree of unsaturation in microalgal fatty acids and total carotenoid content in Nitzschia closterium (Bacillariophyceae) and Isochrysis zhangjiangensis (Chrysophyceae).

The production of metabolites by microalgae is affected by environmental conditions in which they are living. The metabolic responses of two marine microalgae, Nitzschia closterium and Isochrysis zhangjiangensis, to a 3-day UVA-stress and 3-day UVA-recovery treatment were compared, based on their growth, fatty acid profiles and content of total carotenoids. When cultured under photosynthetically active radiation, coupled with UVA treatment, both microalgae underwent a significant increase in their growth during the UVA-recovery period compared to the control. The proportions of polyunsaturated fatty acids, including linoleic acid and eicosapentaenoic acid, as well as total carotenoids, were significantly increased in both microalgae, mainly in the UVA-stress period, but not the UVA-recovery period. The metabolic responses of the two microalgae to UVA treatment were species-dependent and could be utilised to produce microalgal biomass rich in polyunsaturated fatty acids and carotenoids for use as functional food ingredients.