The Discrepancy of Fatty Acid Composition of Astaxanthin Esters and Total Fatty Acids in Photoautotrophic and Heterotrophic Chlorella zofingiensis

Abstract

Chlorella zofingiensis has great potential for astaxanthin and fatty acid production. This study investigated the accumulation of astaxanthin and total fatty acids (TFA), the fatty acid compositions of astaxanthin esters and TFA in photoautotrophic and heterotrophic C. zofingiensis, respectively. The results displayed that in photoautotrophic cells, 18:3 was the most predominant fatty acid, followed by 16:0, 18:2, and 18:1, while astaxanthin mono-esters (mono-AE) contained only 16:0 and 18:0, and astaxanthin di-esters (di-AE) contained 16:0 mostly, followed by 18:1, 18:0, 18:2, and 18:3. C. zofingiensis accumulated the highest level of astaxanthin and TFA under heterotrophic conditions fed with 30 g L −1 glucose. The percentage of 18:1 in TFA, mono-AE, and di-AE increased from 10.05%, 0%, and 17.76% to 35.80%, 14.84%, and 50.12%, respectively; in contrast, the percentages of 18:3 in TFA and di-AE were observed to decrease from 40.42% and 7.59% to 9.56% and 1.30%, respectively, in comparison with those in photoautotrophic ones. The RNA sequencing (RNA-seq) results showed that the expressions of the genes in astaxanthin and fatty acid biosynthetic pathways were increased under this heterotrophic condition. These results indicated differential accumulation of AE and TFA, especially fatty acid compositions of TFA and AE in photoautotrophic and heterotrophic cells, suggesting a positive correlation between astaxanthin and fatty acid biosynthesis.

Progress towards a targeted biorefinery of Chromochloris zofingiensis: a review

“…Heterotrophy allows maximum accumulation of lipids but lower levels of astaxanthin and lutein compared to mixotrophy and phototrophy [ 70 , 124 ]. The higher the glucose concentration the higher the lipid and TFA content in C. zofingiensis [ 74 , 151 ]. Araya et al [ 152 ] grew UTEX 32 phototrophically and found lipid productivity of only 10.95 mg/L/day, whereas Liu et al [ 74 ] obtained 660 mg/L/day and 710 mg/L/day with glucose and molasses respectively.…”

“…The benefits of lipid accumulation by heterotrophic growth are further evidenced by Liu et al [ 112 ]. Fatty acids, especially C18:1, promoted the accumulation of astaxanthin esters and the fatty acid composition of astaxanthin esters was correlated with the TFAs [ 151 ]. C18:1 was promoted by higher sugar concentrations, whereas C18:3 was promoted by lower sugar concentrations [ 74 , 112 ].…”