Poly-(3-hydroxybutyrate) (PHB) is a polyester with biodegradable and biocompatible characteristics and has many potential applications. To reduce the raw material costs and microbial energy consumption during PHB production, cheaper carbon sources such as sucrose were evaluated for the synthesis of PHB under anaerobic conditions. In this study, metabolic network analysis was conducted to construct an optimized pathway for PHB production using sucrose as the sole carbon source and to guide the gene knockout to reduce the generation of mixed acid byproducts. The plasmid pMCS-sacC was constructed to utilize sucrose as a sole carbon source, and the cascaded promoter P_3nirB was used to enhance PHB synthesis under anaerobic conditions. The mixed acid fermentation pathway was knocked out in Escherichia coli S17-1 to reduce the synthesis of byproducts. As a result, PHB yield was improved to 80% in 6.21 g/L cell dry weight by the resulted recombinant Escherichia coli in a 5 L bed fermentation, using sucrose as the sole carbon source under anaerobic conditions. As a result, the production costs of PHB will be significantly reduced.

β-Carotene has extensive applications in the food, pharmaceutical, and cosmetics industries. Traditional chemical synthesis methods face challenges such as byproduct residues and high costs, whereas natural extraction is constrained by low yields and complex processes. Recent advancements in synthetic biology and metabolic engineering have paved the way for the heterologous biosynthesis of β-carotene in microorganisms. Owing to its rapid growth, convenience of genetic manipulation, and suitability for producing apocarotenoids, Escherichia coli is an ideal host for the production of β-carotene and its derivatives, as exemplified by the record production of multiple apocarotenoids in engineered E. coli strains. Here, we summarize the metabolic engineering strategies employed to produce β-carotene in E. coli, including manipulation of the endogenous MEP pathway, introduction of the hybrid MVA pathway, modulation of central carbon metabolism, modification of the cell membrane, and fermentation process optimization. As β-carotene acts as a biosynthetic hub for many carotenoids and apocarotenoids, we also highlighted the importance of efficient β-carotene production for the sustainable preparation of these compounds. This review aims to provide theoretical insights for designing talented β-carotene producers and laying the foundation for the sustainable manufacturing of valuable carotenoids and apocarotenoids.