Exogenous γ-aminobutyric acid promotes biomass and astaxanthin production in Haematococcus pluvialis

Abstract

Haematococcus pluvialis is one of most efficient organisms of producing astaxanthin. To achieve high astaxanthin yield, one strategy in the microalgae industry is to promote growth and biomass of Haematococcus pluvialis. For this purpose, we applied γ-aminobutyric acid (GABA) in the cultivation system and found it could significantly promote the growth of Haematococcus pluvialis, resulting in higher astaxanthin yields. To explore the mechanism of γ-aminobutyric acid induced increase of biomass and astaxanthin production in Haematococcus pluvialis, we conducted both transcriptome and metabolome analyses. The results suggest that the plant hormone signal pathway played a regulatory role in the algae cells, with the genes related to stress resistance being up-regulated. The expression of RuBisco in carbon fixation pathway was also up-regulated, which improved the utilization efficiency of carbon dioxide and biomass under the high light irradiation. Under high light stress, the expression of Lhca2 was up-regulated, and the expression of PTOX related to light protection was up-regulated, while the expression of genes related to astaxanthin synthesis was down-regulated, showing that γ-aminobutyric acid enhanced the photo-protection and stress resistance. Furthermore, we measured the pigment contents, showing that γ-aminobutyric acid increased the contents of chlorophyll and carotene under the condition of nutrient deficiency in the late stage of green vegetative growth. The photosynthesis evaluation reveals that the electron transfer rate (ETR) and non-photochemical quenching (NPQ) of algae cells increased with γ-aminobutyric acid treatment, confirming that γ-aminobutyric acid enhanced the heat dissipation capacity and reduced the light damage. As such, we have demonstrated that exogenous γ-aminobutyric acid can effectively promote the growth of algae cells and increase the biomass and astaxanthin production through the mechanism of improving the stress resistance and photo-protection ability of Haematococcus pluvialis.