Abstract
Carotenoids represent the most abundant lipid-soluble phytochemicals that have been shown to exhibit benefits for nutrition and health. The production of natural carotenoids is not yet cost effective to compete with chemically synthetic ones. Therefore, the demand for natural carotenoids and improved efficiency of carotenoid biosynthesis has driven the investigation of metabolic engineering of native carotenoid producers. In this study, a new Sphingobium sp. was isolated, and it was found that it could use a variety of agro-industrial byproducts like soybean meal, okara, and corn steep liquor to accumulate large amounts of nostoxanthin. Then we tailored it into three mutated strains that instead specifically accumulated ∼5 mg/g of CDW of phytoene, lycopene, and zeaxanthin due to the loss-of-function of the specific enzyme. A high-efficiency targeted engineering carotenoid synthesis platform was constructed in Escherichia coli for identifying the functional roles of candidate genes of carotenoid biosynthetic pathway in Sphingobium sp. To further prolong the metabolic pathway, we engineered the Sphingobium sp. to produce high-titer astaxanthin (10 mg/g of DCW) through balance in the key enzymes β-carotene ketolase (BKT) and β-carotene hydroxylase (CHY). Our study provided more biosynthesis components for bioengineering of carotenoids and highlights the potential of the industrially important bacterium for production of various natural carotenoids.
Highlights
Carotenoids play essential roles in light harvesting and photoprotection in photosynthetic organisms (Niyogi et al, 1997; Niyogi et al, 2001)
A yellow pigmented bacterial strain was isolated from tissue culture plates at Kunming Institute of Botany (KIB), which was revealed to be a rod-shaped and Gram-negative bacterium
Phylogenetic analysis based on the 16S rRNA gene sequences showed that the strain had the highest similarity to Sphingobium sp
Summary
Carotenoids play essential roles in light harvesting and photoprotection in photosynthetic organisms (Niyogi et al, 1997; Niyogi et al, 2001). Animals and humans cannot synthesize carotenoids de novo but take them from the diets, serving as precursors to vitamin A and macula pigments (Grumet et al, 2016). Carotenoids have been applied in food, feed, nutraceuticals, cosmetics, and pharmaceuticals (Cezare-Gomes et al, 2019; Ye et al, 2019). The pathway of carotenoid biosynthesis has been extensively studied in various organisms (Shumskaya and Wurtzel, 2013). Lycopene was conferred diverse functional groups via various carotenoid-modifying enzymes, including lycopene cyclase (CrtY), carotene ketolase (CrtW), and carotene hydroxylase (CrtZ). The cyclic carotenoids derived from lycopene have diverse biological properties and functions (Kim et al, 2014)
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