Converted carotenoid production in Dunaliella salina by using cyclization inhibitors 2-methylimidazole and 3-amino-1,2,4-triazole

Abstract

IntroductionCarotenoids are the group of accessory pigments helping photosynthesis by absorbing light energy from sunlight at certain wavelengths. Their colorful feature and antioxidant properties make them commercially attractive for the biotechnology industry. As photosynthetic organisms, microalgae are a valuable natural source for carotenoid production. One of the well-known species of green microalgae is Dunaliella salina, showing the ability to produce high amounts of natural β-carotene in its unicell in stress conditions like high salt, high temperature, or nitrogen starvation. The carotenoid pathway leading to β-carotene production starts from the colorless carotenoid, phytoene, and continues with the production of linear lycopene molecule, which is a substrate for the enzymes lycopene beta-(LCY-b) and lycopene epsilon cyclases (LCY-e). LCY-b is responsible for the addition of beta cyclic groups to the two ends of lycopene, forming β-carotene. On the other hand, the actions of both LCY-e and LCY-b add one epsilon and one beta ring to the ends of lycopene, resulting in alpha-carotene, and hydrolysis of this molecule leads to lutein production (Figure 1).Most of the pigments in the carotenoid pathway including xanthophylls have an industrial value, with β-carotene, astaxanthin, and lutein having the biggest share in the market. Therefore, evaluating natural producer organisms as a source of different pigments is an attractive field of study.Molecules such as imidazoles, pyridines, and nicotine have been shown to inhibit cyclization of the lycopene molecule, therefore; they have been used to regulate carotenoid biosynthesis in different organisms. As a cyclization inhibitor, nicotine was studied to produce lycopene in both Dunaliella bardawil (Shaish et al., 1990) and Dunaliella salina (Fazeli et al., 2009); however, only trace amounts of the final product were observed. Successful inhibition with nicotine was achieved in another unicellular green alga, Chlorella regularis, only under heterotrophic culture conditions (Ishikawa and Abe, 2004). However, in all cases nicotine severely affected the cell growth in high concentrations due to its toxicity. Recently, another lycopene cyclase inhibitor, triethylamine, was evaluated for lycopene accumulation in D. bardawil (Liang et al., 2016). Although it was recorded at 0.5 pg/cell level for this alga, cell growth was negatively affected by the treatment even at the lowest concentrations (10 ppm). Feofilova et al. (2006) used a nontoxic azine 2-amino-6methylpyridine (MAP) to block cyclization of lycopene Abstract: Carotenoids are vital for most photosynthetic organisms because of their crucial role in prevention of the damage caused by excess light or stress conditions like heat or nutrient deprivation. Some of them are also valuable for biotechnology wıth respect to their colorful feature and antioxidant properties. In this study, a natural β-carotene producer, green microalga Dunaliella salina, was evaluated for its potential to produce different valuable caroten...

Marine Microalgae for Potential Lutein Production

“…From the biotechnological perspective, a number of chemical inhibitors have been tested to regulate the carotenoid biosynthetic pathway in microalgae. For examples, Yildirim et al [24] studied the effect of the addition of 2-methylimidazole in Dunaliella salina and found an increase of 1.7-fold lutein content and a related decline in β-carotene content. This study suggested that 2-methylimidazole preferentially alters lycopene β-cyclase (lcy-b) activity and thus, shifts the carotenogenic pathway from β-carotene to the α-carotene branch.…”

The Carotenogenic Dunaliella salina CCAP 19/20 Produces Enhanced Levels of Carotenoid under Specific Nutrients Limitation

“…A recent study however demonstrated the modified carotenoid production pathways in Dunaliella salina by using cyclization inhibitors 2-methylimidazole (2MI) and 3-amino-1,2,4-triazole (Amitrol). The study found that 2MI was effective in lutein accumulation without affecting cell viability of D. salina when grown at high temperature [36]. …”

Microalgal lutein biosynthesis: Recent trends and challenges to enhance the lutein content in microalgal cell factories

“…Certain chemical inhibitors such as imidazole, pyridine, triethylamine, piperidine, nicotinic acid and nicotine, modify the carotenoids pathway to form specific products in microalgae. Yildirim et al, 2017 suggested that lutein biosynthesis in microalga can be enhanced by adding native biosynthetic pathways inhibitors. In this regard, they used 2methylimidazole (2MI) during the cultivation of Dunaliella salina to inhibit the cyclization reactions in the biosynthesis pathway carotenoids (Yildirim et al, 2017).…”

“…Yildirim et al, 2017 suggested that lutein biosynthesis in microalga can be enhanced by adding native biosynthetic pathways inhibitors. In this regard, they used 2methylimidazole (2MI) during the cultivation of Dunaliella salina to inhibit the cyclization reactions in the biosynthesis pathway carotenoids (Yildirim et al, 2017). The addition of 2MI at a concentration of 1 mM enhanced the lutein content by 1.7folds with a simultaneous reduction in b-carotene content, hence proving that 2MI affects the activity of lycopene bcyclase (LCY-b) that is responsible for a-carotene synthesis (Yildirim et al, 2017).…”

“…In this regard, they used 2methylimidazole (2MI) during the cultivation of Dunaliella salina to inhibit the cyclization reactions in the biosynthesis pathway carotenoids (Yildirim et al, 2017). The addition of 2MI at a concentration of 1 mM enhanced the lutein content by 1.7folds with a simultaneous reduction in b-carotene content, hence proving that 2MI affects the activity of lycopene bcyclase (LCY-b) that is responsible for a-carotene synthesis (Yildirim et al, 2017). They suggested that inhibitor 2 MI-1 mM might be more effective on lycopene b-cyclase than lycopene ϵ-cyclase, and it directs the pathway to the acarotene branch followed by lutein synthesis (Yildirim et al, 2017).…”