The effect of nutrient and phytohormone supplementation on the growth, pigment yields and biochemical composition of newly isolated microalgae

The selection of cultivation conditions for enhancing the productivity and yields of key metabolites are essential for the economic viability of the microalgae-based biorefinery process. The effects of cultivation parameters on microalgal physiology are often species or strain specific. It is hence critical to establish baseline parameters for newly isolated strains and manipulate the culture conditions to optimise their metabolite yields. In this study, five microalgae strains isolated from the west of Ireland were cultivated under varying macronutrient concentrations (NaNO₃ and NaH₂PO₄) and phytohormones (salicylic acid and methyl jasmonate) supplementation to establish their effects on growth rates, photosynthetic pigments and overall biochemical composition. Increasing the medium nitrate content 3-fold resulted in a significant increase in growth, pigments and lipids for 4 of the 5 strains. Methyl jasmonate supplementation caused an increase in carotenoids and lipids in all strains in a dose- and species-specify manner. Salicylic acid treatment induced an increase in protein content in Rhodella sp. APOT_15 and the two chlorophyta strains, K. aperta DMGFW_21 and B. submarina APSW_11. Overall, tailoring the cultivation conditions for each strain can lead to improved strain performance and the identification of key process parameters for the upscaled production of high-value metabolites.