Enhanced Coproduction of Cell-Bound Zeaxanthin and Secreted Exopolysaccharides by Sphingobium sp. via Metabolic Engineering and Optimized Fermentation

Abstract

Zeaxanthin is a value-added carotenoid with wide applications. This study aims to manipulate a generally recognized as safe and carotenoid-producing bacterium, Sphingobium sp., for enhanced production of zeaxanthin and exopolysaccharides. First, whole-genome sequencing and analysis of pathway genes were applied to define the carotenoid pathway in Sphingobium sp. Second, a Sphingobium transformation system was established to engineer metabolite flux into zeaxanthin. By a combination of chemical mutagenesis and removal of bottlenecks of carotenoid biosynthesis via overexpression of three rate-limiting enzymes, the genetically modified Sphingobium DIZ strain produced 21.26 mg/g dry cell weight of zeaxanthin, which was about 4-fold higher than the wild type. Upon optimization of culture conditions, the DIZ strain produced 479.5 mg/L of zeaxanthin with the productivity of 4.99 mg/L/h and 21.9 g/L of exopolysaccharides using a fed-batch fermentation strategy. This study represents the first genetic manipulation of Sphingobium sp., a biotechnologically important bacterium, for high-yield production of value-added metabolites.

Engineering Sphingobium sp. to Accumulate Various Carotenoids Using Agro-Industrial Byproducts

“…Sphingobium sp. KIB was stored in the China General Microbiological Culture Collection Center (CGMCC No.12394), which was isolated from Kunming Institute of Botany ( Liu et al, 2019 ). Sphingobium sp.…”

“…Then these four plasmids were transformed using electrotransformation into Sphingobium sp. KIB-zea ( Liu et al, 2019 ).…”

“…Carotenoid analysis was performed according to Liu et al (2019) . Acetone was used to extract carotenoids.…”

“…Currently, commercial natural carotenoids (e.g., β-carotene, astaxanthin, and zeaxanthin) are extracted from a small number of specific plant tissues and a few microbes ( Liu et al, 2019 ). Microbial production is the major source of natural-origin carotenoids, such as β-carotene and astaxanthin, because of higher growth rates and contents ( Zhang et al, 2018 ).…”

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“…Hence, Sphingobium sp. KIB could serve as a starting strain for the efficient production of zeaxanthin (Liu et al, 2019) and possibly other carotenoids using…”