Spectrophotometry can monitor changes in algal metabolism triggered by nutrient deficiency in Nannochloropsis oculata cultured under various light-emitting diode light regimes
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Efficient production of beneficial metabolites by microalgae using light-emitting diodes (LED) is attracting more interest. In batch cultures, metabolic changes that occur with nutrient deficiency over time must be monitored to estimate the metabolite content. Our previous study showed that nutrient deficiency in Nannochloropsis oculata can be briefly evaluated by measuring the absorption ratio at 490 and 680 nm (Abs490/Abs680). However, little is known about the relation with this ratio and metabolic change, particularly in LED light-conditioned cultures. In this study, we investigate if Abs490/Abs680 can be an indicator of the biochemical status of N. oculata cultured under various LED color regimes. Three LED treatments were used: Blue (B), Blue + Red (BR), and Red (R). In all LED treatments, the Abs490/Abs680 decreased for several days and then increased when phosphate was limited or non-existent. The trends in the C16:0 and C20:5ɷ3 proportions and chlorophyll a content commonly changed at the turning points of the Abs490/Abs680. Furthermore, significant correlations were found among the metabolic state and absorption ratio, except in treatment R. We suggest that spectrophotometry can be used for monitoring metabolic changes in N. oculata cultures under various LED irradiance, unless there is excessive 630 nm-red light exposure.
KeywordsFatty acid composition LED Metabolism Nannochloropsis oculata Nutrient deficiency Spectrophotometry
We would like to thank Professor Shunsuke Koshio and Manabu Ishikawa and assistant professor Saichiro Yokoyama for lending us the gas chromatography. We would like to thank associate professor Hikaru Endo for the review and discussion. We are grateful to Iris Ann Borlongan and Viliame Pita Waqalevu for some advice on how to brush up the paper. We would like to thank Enago (www.enago.jp) for the English language review.
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