Metabolic engineering of Starmerella bombicola for the production of sophorolipids

Abstract

Sophorolipids (SLs), a class of glycolipid biosurfactants, are naturally synthesized by Starmerella bombicola. Composed of sophorose and fatty acids, SLs exhibit excellent emulsification, reduced surface tension, low toxicity, and high biodegradability, making them promising for applications in food, detergent, and agricultural industries. In this study, we screened a S. bombicola capable of efficiently and stably synthesizing SLs through multiple rounds of rejuvenation as the wild-type strain. First, we knocked out PXA1, a gene critical for fatty acid β-oxidation (a competing pathway for SLs production). This weakened β-oxidation and generated the P1 strain. The SLs titer of the P1 strain reached 66.96 ± 4.29 g/L, representing a 50.5% increase compared to the wild-type strain (48.11 ± 3.50 g/L). Subsequently, by enhancing the expression of CYP52M1, a key enzyme in the fatty acid ω-oxidation pathway, we constructed the PC1 strain, which achieved an SLs titer of 88.50 ± 4.91 g/L, a 98.8% improvement over the wild-type strain. Finally, we scaled up the fermentation of the PC1 strain in a 5 L fermenter, and through fed-batch fermentation, the SLs titer reached 232.27 ± 13.83 g/L on the 7th day. This study shows that engineered S. bombicola strains can efficiently produce high SLs titers, making large-scale biosynthesis feasible.

Keywords

Sophorolipids / Starmerella bombicola / Metabolic engineering / β-oxidation / Uridine glucose diphosphate

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Funding

the Key Research and Development Program of China(2024YFA0917901-05); the Key Research and Development Program of China (2023YFC3402400); Innovative Research Group Project of the National Natural Science Foundation of China(No. 32271533)