Exogenous prolinebooststheco-accumulation ofastaxanthin and biomassin stress-induced Haematococcus pluvialis.

This paper aims to explore the role of proline (Pro) in the production of biomass and astaxanthin (AST) in stress-induced Haematococcus pluvialis. The astaxanthin content and productivity were 24.02 mg g-1 and 2.22 mg/L d-1 under abiotic stresses, respectively. After 100 µM Pro supplementation, the biomass, AST and lipid contents reached 1.43 g/L, 29.91 mg g-1 and 56.79 %, which were enhanced by 19.16 %, 33.52 % and 11.08 %, respectively, compared to the control. Pro-treated regulated chlorophyll, carbohydrate and protein accumulation and upregulated carotenogenic, lipogenic and antioxidant enzymes-associated gene levels; as well as increased endogenous Pro content, but reduced ROS (Reactive oxygen species) and MDA (Malondialdehyde) levels and alleviated oxidative stress, which might be involved in AST biosynthesis. Further data showed Pro has a positive role in biomass and AST coaccumulation in different H. pluvialis species, suggesting application of Pro was an effective strategy to improve AST productivity of H. pluvialis.

Myo-inositol facilitates astaxanthin and lipid coproduction in Haematococcus pluvialis by regulating oxidative stress and ethylene signalling.

In the present study, exogenous myo-inositol (MI) was applied to induce natural astaxanthin and biolipid accumulation in Haematococcus pluvialis. Under 200 µM MI, algal cells exhibited 62.11 % and 34.67 % increases in astaxanthin and lipid content, respectively, compared to the control. The carotenogenesis and lipogenesis genes were upregulated by induction of MI. Interestingly, MI addition elevated the ethylene (ETH) content and activated antioxidant enzyme-associated gene levels, which could be involved in alleviating oxidative stress. Further data showed that the ETH signal played a positive function in stimulating astaxanthin biosynthesis under MI induction. Supplementation with ethephon plus MI boosted the astaxanthin content to 33.08 ± 0.03 mg g-1 by further upregulating astaxanthin biosynthesis genes and blocking reactive oxidative species (ROS) levels, and vice versa under ETH inhibition. This study provides a potential induction approach for natural astaxanthin production and explains the role of ethylene signalling in regulating astaxanthin synthesis by H. pluvialis.

Promoting lutein production from the novel alga Acutodesmus sp. by melatonin induction.

In the current research, a novel microalgae strain was isolated from Yajiageng Red Rock Beach and identified as Acutodesmus sp. HLGY. To obtain high-efficiency production of lutein from algae, the feasibility of using melatonin (MT) to increase lutein yield of Acutodesmus sp. HLGY was evaluated. Under the 7.5 µM MT treatment, the lutein content and lutein productivity were 17.44 mg g-1 and 46.50 mg L-1 d-1, which were 1.53 times those of the control. Furthermore, exogenous MT increased the transcripts of key lutein synthesis- and antioxidant enzyme-related genes. Simultaneously, the carbohydrate, protein, and cellular reactive oxygen species (ROS) levels and lipid content were suppressed. More importantly, the ethylene and γ-aminobutyric acid contents were markedly increased by MT, which may be linked to the increase in lutein biosynthesis. This study proposes a valuable biotechnological approach for lutein production via a novel Acutodesmus sp. strain using MT induction and provides insights into the role of MT in promoting lutein biosynthesis.