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

Abstract

Blue‐green light is known to maximize the degree of fatty acid (FA) unsaturation in microalgae. However, knowledge on the particular waveband responsible for this stimulation of FA desaturation and its impact on the pigment composition in microalgae remains limited. In this study, Acutodesmus obliquus was cultivated for 96 h at 15°C with different light spectra (380–700 nm, 470–700 nm, 520–700 nm, 600–700 nm, and dark controls). Growth was monitored daily, and qualitative characterization of the microalgal FA composition was achieved via gas chromatography coupled with electron impact ionization mass spectrometry (GC‐EI/MS). Additionally, a quantitative analysis of microalgal pigments was performed using high‐performance liquid chromatography with diode array detection (HPLC‐DAD). Spectra that included wavelengths between 470 and 520 nm led to a significantly higher percentage of the polyunsaturated fatty acids (PUFA) 18:3 and 16:4, compared to all other light conditions. However, no significant differences between the red light cultivations and the heterotrophic dark controls were observed for the FA 18:3 and 16:4. These results indicate, that exclusively the blue‐green light waveband between 470 and 520 nm is responsible for a maximized FA unsaturation in A. obliquus. Furthermore, the growth and production of pigments were impaired if blue‐green light (380–520 nm) was absent in the light spectrum. This knowledge can contribute to achieving a suitable microalgal pigment and FA composition for industrial purposes and must be considered in spectrally selective microalgae cultivation systems.

Impact of green and blue‐green light on the growth, pigment concentration, and fatty acid unsaturation in the microalga Monoraphidium braunii

“…This was also observed in our recent study on the microalgae A. obliquus and might explain the high biomass production under white light, which contains red light and blue light (Figure 1). 18 …”

“…The cultivations were performed in triplicates for each tested condition in two independent experiments, and the means ± standard errors were calculated from the values obtained. All statistical tests were done according to Helamieh et al 18 …”

“…The pre-cultivation and determination of cell dry weight (CDW) were performed according to Ref. [5,18].…”

“…Furthermore, blue and green light can influence the composition of photosynthetic pigments and fatty acids (FA). Recently, we have reported that blue‐green light between 450 and 550 nm is required for a maximized FA unsaturation and a maximized pigment concentration in the green microalga Acutodesmus obliquus 18 . These blue‐green light‐triggered physiological reactions might be related to a light activation of FA desaturase enzymes and the rearrangement processes of thylakoid membranes of chloroplasts 5,19–21 .…”

“…Recently, we have reported that blue-green light between 450 and 550 nm is required for a maximized FA unsaturation and a maximized pigment concentration in the green microalga Acutodesmus obliquus. 18 These blue-green light-triggered physiological reactions might be related to a light activation of FA desaturase enzymes and the rearrangement processes of thylakoid membranes of chloroplasts. 5,[19][20][21] Many of such light-triggered processes in organisms are highly conserved in the evolution of organisms.…”