Growth and fatty acid composition of Acutodesmus obliquus under different light spectra and temperatures

Abstract

The combined impact of temperature and light spectra on the fatty acid (FA) composition in microalgae has been sparsely investigated. The aim of this study was to investigate the interactions of light and temperature on the FA composition in Acutodesmus obliquus. For this purpose, A. obliquus was cultivated with different temperatures (20, 30, and 35 C), as well as broad light spectra (blue, green, and red light). Growth and FA composition were monitored daily. Microalgal FA were extracted, and a qualitative characterization was done by gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Compared to red light, green and blue light caused a higher percentage of the polyunsaturated fatty acids (PUFA) 16:4, 18:3, and 18:4, at all temperatures. The highest total percentage of these PUFA were observed at the lowest cultivation temperature and blue and green light. These data imply that a combination of lower temperatures and blue-green light (450-550 nm) positively influences the activity of specific FA-desaturases in A. obliquus. Additionally, a lower 16:1 trans/cis ratio was observed upon green and blue light treatment and lower cultivation temperatures. Remarkably, green light treatment resulted in a comparably high growth under all tested conditions. Therefore, a higher content of green light, compared to blue light might additionally lead to a higher biomass concentration. Microalgae cultivation with low temperatures and green light might therefore result in a suitable FA composition for the food industry and a comparably high biomass production.

Blue‐green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus

“…It was shown that wavelengths below 500 nm combined with red light (600-700 nm) lead to higher photosynthetic efficiency and growth in A. obliquus, compared to monochromatic red light (600-700 nm) (Osterthun, Helamieh, et al, 2021). The FA composition is in accordance with several published data on the same microalgal strain (Abomohra et al, 2013;Helamieh et al, 2021). However, due to the lower cultivation temperature, a higher relative percentage of PUFA, such as 18:3 and 16:4 was observed in this study.…”

“…The elevation of the FA16:1 in the heterotrophic dark treated samples is remarkable, even though no immediate explanation for it can be found in the literature. In addition, different from (Helamieh et al, 2021), no impact of the light conditions on the relative percentage of 18:4 in A. obliquus was observed (data not shown).…”

“…However, the used cultivation temperature is lower than the optimum temperature of this species, which is around 30 C (Hindersin et al, 2012). Therefore, the biomass production was lower than in previous studies with the same strain, which were performed around the optimum temperature of this species (Admirasari et al, 2022;Helamieh et al, 2021;Reymann et al, 2020). In addition, the growth under monochromatic red light was significantly lower compared to all other tested light spectra (Figure 2).…”

“…Details of the analytical method can be found elsewhere (Helamieh et al, 2021). FA extraction: The frozen samples were thawed and 0.0025 g CDW was used for the FA-extractions.…”

“…A modified Folch extraction was employed to extract the FA (Ichihara & Fukubayashi, 2010;Reich et al, 2012Reich et al, , 2013. The solvents of the extraction were evaporated under a constant and gentle stream of nitrogen and the transesterification was done according to (Helamieh et al, 2021).…”