From K-snack to copolymer: conversion of silkworm pupa oil into poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by engineered Cupriavidus necator H16.

Abstract

Silkworm pupae are continuously generated as a major byproduct of the silk industry and have traditionally been utilized as a food resource in Korea. However, limitations in direct consumption motivate alternative valorization of their lipid-rich composition for value-added bioproducts. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that silkworm pupa oil (SPO) consists of approximately 54% oleic acid, 29% linoleic acid, 17% palmitic acid, and minor amounts of cyclopropane fatty acids. Based on this composition, this study evaluated the feasibility of producing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] using engineered Cupriavidus necator H16 with SPO as a sustainable substrate. Compared with other carbon sources, SPO supported the highest biomass formation, which was 2.64-fold higher than fructose and 1.42-fold higher than bean oil in flask cultures, demonstrating its potential as an efficient substrate. Supplementation with 1.0% fructose as an auxiliary carbon source further increased dry cell weight (DCW) and total PHA accumulation by up to 20%. To improve emulsification, various emulsifiers were screened, and 0.1% Tween 20 enhanced DCW and PHA production by 1.4-fold and 1.55-fold, respectively. The resulting film exhibited a tensile strength of 6.0 ± 0.6 MPa and an elongation at break of 53.4 ± 4.6% and showed approximately 90% degradation after 7 days by Microbulbifer sp. SOL66. Overall, this study demonstrates that SPO is a promising and sustainable carbon source for PHA production, highlighting the valorization of silk industry byproducts into high-value biopolymeric materials.

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