Carotenoids are yellow to red pigments synthesized by all photosynthetic organisms. Lutein, β-carotene, and zeaxanthin are essential carotenoids for human health, serving as provitamin A or retina pigments.
Human and animals have to obtain these carotenoids from their diets that commonly consist of quite low levels of the pigments. As a result, vitamin A deficiency is a public health problem in developing countries.
High dietary intake of zeaxanthin and lutein proved to decrease the risk of age-related macular degeneration, the main cause of blindness of elder people.
In contrast to lutein and β-carotene that can derive from marigold flowers and the green alga Dunelialla salina respectively on large scales, no commercial sources of natural zeaxanthin are available up to date.
Recently, the research team led by professor HUANG Junchao from Kunming Institute of Botany, Chinese Academy of Sciences (KIB/CAS) established a mutant of Chlorella zofingiensis (CZ-bkt1), which could accumulate high amounts of zeaxanthin as well as lutein and β-carotene.
CZ-bkt1 was achieved by treating the algal cells with a chemical mutagen followed by a colour-based colony screening approach. CZ-bkt1 was found to consist of a dysfunctional carotenoid ketolase, leading to the accumulation of zeaxanthin rather than its downstream ketocarotenoid astaxanthin.
Light irradiation, glucose, NaCl, and nitrogen deficiency all induced CZ-bkt1 to accumulate zeaxanthin. CZ-bkt1 accumulated zeaxanthin up to 7.00 mg/g when induced by high light irradiation and nitrogen deficiency, and 36.79 mg/L by additional feeding with glucose. Furthermore, in addition to zeaxanthin, CZ-bkt1 also accumulated high amounts of β-carotene (7.18 mg/g or 34.64±1.39 mg/L) and lutein (13.81 mg/g or 33.97mg/L). CZ-bkt1 is the sole species up to date with the ability to accumulate high amounts of the three carotenoids that are important for human health.
The results were published in Journal of Agricultural and Food Chemistry with the title “Induced high-yield production of zeaxanthin, lutein, and β-carotene by a mutant of Chlorella zofingiensis”.
This study was funded by research grants from Yunnan Provincial Science and Technology Department (2014FA041 and 2010BB008).
Figure 1. Phenotype of WT and CZ-bkt1 cultured (A) without or (B) with glucose and (C, D) their pigment profiles. Pigments in UHPLC traces of WT (red) and CZ-bkt1 (blue) are as follows: 1, free astaxanthin; 2, keto-lutein; 3, lutein + zeaxanthin; 4, canthaxanthin; 5, chlorophyll b; 6, astaxanthin monoester; 7, keto-lutein monoester; 8, adonixanthin monoester; 9, β-carotene; 10, astaxanthin diester. (Image by KIB)
Contact:
YANG Mei
General Office
Kunming Institute of Botany, CAS
Email: yangmei@mail.kib.ac.cn
(Editor: YANG Mei)
