Construction of a Microbial Consortium for the De Novo Synthesis of Butyl Butyrate from Renewable Resources

Microbial Astaxanthin Synthesis by Komagataella phaffii through Metabolic and Fermentation Engineering

Astaxanthin is a kind of carotenoid with a strong antioxidant ability, which has shown broad applications in the areas of healthcare, medicine, cosmetics, food additives, and aquaculture. With the increasing demand for natural products, the microbial production of astaxanthin has become a new hot spot. In this study, the astaxanthin synthesis pathway was first metabolically constructed in Komagataella phaffii (K. phaffii)(Pichia pastoris). By exploring the combination of different promoters, astaxanthin producers were obtained. Then, the key enzymes in the astaxanthin synthesis pathway were explored, and different enzyme assembly strategies and an increase in NADPH supply were used to improve the astaxanthin production. Furthermore, fermentation parameters including temperature, the concentration of the carbon source, nitrogen sources, metal ions, BHT (2,6-di-tert-butyl-4-methylphenol), and Tween-80 were comprehensively investigated for the microbial growth and astaxanthin synthesis. Finally, the astaxanthin production reached 716.13 mg/L by fed-batch fermentation in a 5 L bioreactor, which was the highest production of astaxanthin synthesized by K. phaffii.

Screening and engineering of lycopene-producing strain Rhodococcus jostii for bio-upcycling of poly(ethylene terephthalate) waste

Poly(ethylene terephthalate) (PET) is a widely used plastic, but its improper disposal has caused serious environmental pollution. The development of bioconversion for PET waste into high-value chemicals has gained significant attention as an innovative solution. In this study, a novel guided screening strategy involving mixed-bacteria fermentation and partitioned purification (MBF) was proposed to first successful isolate Rhodococcus jostii LETBE 8896, a strain capable of naturally producing 4 μg/L of lycopene from PET hydrolysate. Transcriptomic analysis identified the methylerythritol 4-phosphate (MEP) pathway as key to lycopene biosynthesis, with IspG identified as a critical regulatory enzyme. R. jostii with ispG overexpression enhanced lycopene production, with 819 μg/L in the simulated PET hydrolysate and 650 μg/L in the PET hydrolysate. Additionally, the use of butylated hydroxytoluene (BHT) as an antioxidant significantly improved lycopene production at 1 L scale level, achieving a maximum yield of 1865 μg/L with a molar conversion rate of 50.36 % from the PET hydrolysate, the highest reported for PET hydrolysate to date. These findings highlight the dual potential of R. jostii as a chassis strain for high-value chemical production and as a sustainable solution for PET upcycling. This study provides a novel approach to plastic waste management, contributing to the circular economy and global sustainability goals.

Strategies and tools to construct stable and efficient artificial coculture systems as biosynthetic platforms for biomass conversion

Inspired by the natural symbiotic relationships between diverse microbial members, researchers recently focused on modifying microbial chassis to create artificial coculture systems using synthetic biology tools. An increasing number of scientists are now exploring these systems as innovative biosynthetic platforms for biomass conversion. While significant advancements have been achieved, challenges remain in maintaining the stability and productivity of these systems. Sustaining an optimal population ratio over a long time period and balancing anabolism and catabolism during cultivation have proven difficult. Key issues, such as competitive or antagonistic relationships between microbial members, as well as metabolic imbalances and maladaptation, are critical factors affecting the stability and productivity of artificial coculture systems. In this article, we critically review current strategies and methods for improving the stability and productivity of these systems, with a focus on recent progress in biomass conversion. We also provide insights into future research directions, laying the groundwork for further development of artificial coculture biosynthetic platforms.

Bioproduction of Geranyl Esters by Integrating Microbial Biosynthesis and Enzymatic Conversion

Geranyl esters (GEs) are valuable monoterpene esters derived from the esterification of geraniol and various carboxylic acids with a range of unique aromas and properties, making them valuable in perfumery, pharmaceutical, and cosmetic applications. Lipase-mediated esterification is considered to be a sustainable process but is challenged by the lack of a compatible catalytic method in conjunction with a customized microbial biosynthesis of geraniol. In this study, we developed an integrated process to convert glycerol and various carboxylates into GEs. The process includes microbial biosynthesis of geraniol using metabolically engineered Escherichia coli and enzymatic conversion of geraniol into GEs in a fermentation medium-organic biphasic system using an immobilized lipase. The enzymatic step for esterifying the target carboxylates with geraniol achieved >90% conversion under the optimized condition. Coupled with the geraniol from microbial fermentation, 0.59 g/L geranyl butyrate and 1.04 g/L geranyl hexanoate were produced subsequently, demonstrating the feasibility of converting renewable source into monoterpene esters through this integrated process, which bypassed feeding extra geraniol in the conventional lipase-mediated GE synthesis.

Recent developments in enzymatic and microbial biosynthesis of flavor and fragrance molecules

Flavors and fragrances are an important class of specialty chemicals for which interest in biomanufacturing has risen during recent years. These naturally occurring compounds are often amenable to biosynthesis using purified enzyme catalysts or metabolically engineered microbial cells in fermentation processes. In this review, we provide a brief overview of the categories of molecules that have received the greatest interest, both academically and industrially, by examining scholarly publications as well as patent literature. Overall, we seek to highlight innovations in the key reaction steps and microbial hosts used in flavor and fragrance manufacturing.

Microbial cell factory for butyl butyrate production: Knowledges and perspectives

Butyl butyrate is a short-chain fatty acid ester (C8) with a fruity aroma. It has broad prospects in the fields of foods, cosmetics and biofuels. At present, butyl butyrate is produced by chemical synthesis in the industry, but it is highly dependent on petroleum-based products. The growing concerns regarding the future scarcity of fossil fuels have been strongly promoted the transition from traditional fossil fuels and products to renewable bioenergy and biochemicals. Therefore, it is necessary to develop a green biochemical technology to replace traditional petroleum-based materials. In recent years, microorganisms such as Escherichia coli and Clostridium have been engineered to serve as cell factories for the sustainable one-pot production of short-chain fatty acid esters, including butyl butyrate. This opinion highlights the recent development in the use of lipases and alcohol acyltransferases (AATs) for butyl butyrate production in microbial fermentation, as well as future perspectives.

Metabolic and Bioprocess Engineering of Clostridium tyrobutyricum for Butyl Butyrate Production on Xylose and Shrimp Shell Waste

Microbial conversion of agri-food waste to valuable compounds offers a sustainable route to develop the bioeconomy and contribute to sustainable biorefinery. Clostridium tyrobutyricum displays a series of native traits suitable for high productivity conversion of agri-food waste, which make it a promising host for the production of various compounds, such as the short-chain fatty acids and their derivative esters products. In this study, a butanol synthetic pathway was constructed in C. tyrobutyricum, and then efficient butyl butyrate production through in situ esterification was achieved by the supplementation of lipase into the fermentation. The butyryl-CoA/acyl-CoA transferase (cat1) was overexpressed to balance the ratio between precursors butyrate and butanol. Then, a suitable fermentation medium for butyl butyrate production was obtained with xylose as the sole carbon source and shrimp shell waste as the sole nitrogen source. Ultimately, 5.9 g/L of butyl butyrate with a selectivity of 100%, and a productivity of 0.03 g/L·h was achieved under xylose and shrimp shell waste with batch fermentation in a 5 L bioreactor. Transcriptome analyses exhibited an increase in the expression of genes related to the xylose metabolism, nitrogen metabolism, and amino acid metabolism and transport, which reveal the mechanism for the synergistic utilization of xylose and shrimp shell waste. This study presents a novel approach for utilizing xylose and shrimp shell waste to produce butyl butyrate by using an anaerobic fermentative platform based on C. tyrobutyricum. This innovative fermentation medium could save the cost of nitrogen sources (~97%) and open up possibilities for converting agri-food waste into other high-value products.

Engineering of Clostridium tyrobutyricum for butyric acid and butyl butyrate production from cassava starch

Clostridium tyrobutyricum has been successfully engineered to produce butyrate, butanol, butyl butyrate, and γ-aminobutyric acid. It would be interesting to produce bio-chemicals and bio-fuels directly using starch from non-food crop, e.g., cassava, by engineered C. tyrobutyricum. In this study, heterologous α-amylases were screened and expressed in C. tyrobutyricum, resulting in successfully starch hydrolyzation. Furthermore, α-glucosidase (AgluI) was co-expressed with α-amylases, resulting in enhancement in the capacity of starch hydrolyzation and butyrate production. When increasing the cassava starch concentration to 100 g/L, the engineered strain CTAA05 produced 27.0 g/L butyrate. In addition, when introducing butyl butyrate synthetic pathway, strain MU3-AAV produced 26.8 g/L butyl butyrate with 100 g/L cassava starch as substrate. This study showed a generalizable framework to engineered anaerobes for anaerobic production of bio-chemicals and bio-fuels from starchy biomass.