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

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.

Seasonal Variation of Plant Defense Inductor Ellagitannins in Strawberry Leaves under Field Conditions for Phytosanitary Technological Applications

Many natural compounds can activate the plant immunity, and for this reason, they have attracted special interest in crop disease management. Previously, we isolated from strawberry leaves an ellagitannin (HeT), which elicits plant defense responses. In this research, we investigated bioactive compounds from field-collected strawberry leaves capable of inducing defense responses in Arabidopsis thaliana against a bacterial pathogen. Methanolic extracts of strawberry leaves sampled at different months were obtained and compared. The highest content of total soluble phenolic compounds was found in the methanolic extracts of leaves sampled in December (DME). The defense response induced in A. thaliana by DME was attributed to two ellagitannins, the HeT and galloyl-HHDP-glucose. Both compounds exhibited phytoprotective effects against Pseudomonas viridiflava and induced the expression of PDF1.2 and PR1 genes. These results provide an economic value to strawberry leaves, normally discarded at the end of the harvest stage of the crop, as a raw material for plant health enhancer bioinputs.