Abstract
Chromochloris zofingiensis has obtained particular interest as a promising candidate for natural astaxanthin production. In this study, we established a two-stage heterotrophic cultivation process, by using which both the growth of C. zofingiensis and astaxanthin accumulation are substantially enhanced. Specifically, the ultrahigh biomass concentration of 221.3 g L−1 was achieved under the optimum culture conditions in 7.5 L fermenter during 12 days. When scaled-up in the 500 L fermentor, the biomass yield reached 182.3 g L−1 in 9 days, while the astaxanthin content was 0.068% of DW. To further promote astaxanthin accumulation, gibberellic Acid-3 (GA3) was screened from a variety of phytohormones and was combined with increased C/N ratio and NaCl concentration for induction. When C. zofingiensis was grown with the two-stage cultivation strategy, the astaxanthin yield reached 0.318 g L−1, of which the biomass yield was 235.4 g L−1 and astaxanthin content was 0.144% of DW. The content of the total fatty acids increased from 23 to 42% of DW simultaneously. Such an astaxanthin yield was 5.4-fold higher than the reported highest record and surpassed the level of Haematococcus pluvialis. This study demonstrated that heterotrophic cultivation of C. zofingiensis is competitive for industrial astaxanthin production.
Highlights
Astaxanthin (3, 3′-dihydroxy-β, β-carotene-4, 4′-dione) is a high-value red ketocarotenoid and possesses a wide range of commercial applications in food, feed, cosmetics, pharmaceuticals, and nutraceuticals due to its powerful antioxidative activity, pigmentation function, and many other bioactivities (Ambati et al, 2014; Liu et al, 2014)
An ultrahigh biomass concentration of 153 g L−1 was achieved in the modified Endo culture medium containing NH4Cl as the nitrogen source
Within the temperature range of 24–28°C, C. zofingiensis showed a rapid growth trend, and the highest biomass concentration of 149.5 g L−1 was achieved at 26°C after 9 days of cultivation (Figure 2B)
Summary
Astaxanthin (3, 3′-dihydroxy-β, β-carotene-4, 4′-dione) is a high-value red ketocarotenoid and possesses a wide range of commercial applications in food, feed, cosmetics, pharmaceuticals, and nutraceuticals due to its powerful antioxidative activity, pigmentation function, and many other bioactivities (Ambati et al, 2014; Liu et al, 2014). Astaxanthin can be synthesized artificially or produced by organisms such as green microalgae. The (3S, 3′S) isoform is the most abundant stereoisomer of the natural astaxanthin produced by green microalgae, whereas the artificially synthesized astaxanthin contains a mixture of isomers (3S, 3′S), (3R, 3S), and (3R, 3′R) at the ratio of 1:2:1 (Li et al, 2020). The antioxidant activity of artificially synthesized astaxanthin is 20 times lower than its natural counterpart and is not allowed to apply in human foods in many countries (Rodríguez-Sáiz et al, 2010; Shah et al, 2016). H. pluvialis is the major resource of natural astaxanthin production strain in the industry, as they can accumulate up to 5–6% of astaxanthin on dry weight (Yang et al, 2016). Astaxanthin production by using H. pluvialis is faced with technical bottlenecks such as high cost, low production efficiency, and inevitable contamination by the pathogenic fungus in outdoor mass cultivation (Liu et al, 2013)
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