Enhancing Fatty Acid Production of Saccharomyces cerevisiae as an Animal Feed Supplement

Increased accumulation of fatty acids in engineered Saccharomyces cerevisiae by co-overexpression of interorganelle tethering protein and lipases

Fatty acids (FAs) and their derivatives are versatile chemicals widely used in various industries. Synthetic biology, using microbial cell factories, emerges as a promising alternative technology for FA production. To enhance the production capacity of these microbial chassis, additional engineering strategies are imperative. Based on the comparison of the morphological changes of lipid droplets (LDs) between oleaginous and non-oleaginous yeasts, we developed a new engineering strategy to increase the accumulation of FAs in Saccharomyces cerevisiae through manipulation of regulation factor and lipases related to LD. The increased biogenesis of LDs, achieved by overexpressing the interorganelle tethering protein Mdm1, coupled with the accelerated degradation of LDs through upregulated lipases, resulted in a 10.70-fold increase in total FAs production. Co-overexpression of Mdm1 and selected lipases significantly improved the biosynthesis of FAs and linoleic acid in the engineered S. cerevisiae. The efficient LD-based metabolic engineering strategy presented in this study holds the potential to advance the high-level production of FAs and their derivatives in microbial cell factories.

Metabolic engineering of Saccharomyces cerevisiae for the synthesis of valuable chemicals

In the twenty first century, biotechnology offers great opportunities and solutions to climate change mitigation, energy and food security and resource efficiency. The use of metabolic engineering to modify microorganisms for producing industrially significant chemicals is developing and becoming a trend. As a famous, generally recognized as a safe (GRAS) model microorganism, Saccharomyces cerevisiae is widely used due to its excellent operational convenience and high fermentation efficiency. This review summarizes recent advancements in the field of using metabolic engineering strategies to construct engineered S. cerevisiae over the past ten years. Five different types of compounds are classified by their metabolites, and the modified metabolic pathways and strategies are summarized and discussed independently. This review may provide guidance for future metabolic engineering efforts toward such compounds and analogues. Additionally, the limitations of S. cerevisiae as a cell factory and its future trends are comprehensively discussed.

De Novo Biosynthesis of Free Vaccenic Acid with a Low Content of Oleic Acid in Saccharomyces cerevisiae

Omega-7 (ω-7) fatty acids have potential application in the fields of nutraceutical, agricultural, and food industry. The natural ω-7 fatty acids are currently from plants or vegetable oils, which are unsustainable and limited by the availability of plant sources. Here, we developed an innovative biosynthetic route to produce vaccenic acid (C18:1 ω-7) while minimizing oleic acid (C18:1 ω-9) content in Saccharomyces cerevisiae. We have engineered S. cerevisiaeto produce C18:1 ω-7 by expressing a fatty acid elongase from Rattus norvegicus. To reduce the content of C18:1 ω-9, the endogenous desaturase Ole1 was replaced by the desaturase, which has specific activity on palmitoyl-coenzyme A (C16:0-CoA). Finally, the production of free C18:1 ω-7 was improved by optimizing the source of cytochrome b5 and overexpressing endoplasmic reticulum chaperones. After combining these strategies, the yield of C18:1 ω-7 was increased from 0 to 9.3 mg/g DCW and C18:1 ω-9 was decreased from 25.2 mg/g DCW to 1.6 mg/g DCW. This work shows a de novo synthetic pathway to produce the highest amount of free C18:1 ω-7 with a low content of C18:1 ω-9 in S. cerevisiae.

Studying the impact of cell age on the yeast growth behaviour of Saccharomyces pastorianus var. carlsbergensis by magnetic separation

Despite the fact that yeast is a widely used microorganism in the food, beverage, and pharmaceutical industries, the impact of viability and age distribution on cultivation performance has yet to be fully understood. For a detailed analysis of fermentation performance and physiological state, we introduced a method of magnetic batch separation to isolate daughter and mother cells from a heterogeneous culture. By binding functionalised iron oxide nanoparticles, it is possible to separate the chitin-enriched bud scars by way of a linker protein. This reveals that low viability cultures with a high daughter cell content perform similarly to a high viability culture with a low daughter cell content. Magnetic separation results in the daughter cell fraction (>95%) showing a 21% higher growth rate in aerobic conditions than mother cells and a 52% higher rate under anaerobic conditions. These findings emphasise the importance of viability and age during cultivation and are the first step towards improving the efficiency of yeast-based processes.

Expression of Yarrowia lipolytica acetyl-CoA carboxylase in Saccharomyces cerevisiae and its effect on in-vivo accumulation of Malonyl-CoA

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Novel S. cerevisiae strain with tetracycline repressible ACC1 promoter.

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Functional expression of Y. lipolytica ACC1 in S. cerevisiae.

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Higher malonyl-CoA concentration achieved with Y. lipolytica ACC1 gene.

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S. cerevisiae Acc1p seems to interact with the heterologous Y. lipolytica Acc1p.

Malonyl-CoA is an energy-rich molecule formed by the ATP-dependent carboxylation of acetyl coenzyme A catalyzed by acetyl-CoA carboxylase. This molecule is an important precursor for many biotechnologically interesting compounds such as flavonoids, polyketides, and fatty acids. The yeast Saccharomyces cerevisiae remains one of the preferred cell factories, but has a limited capacity to produce malonyl-CoA compared to oleaginous organisms. We developed a new S. cerevisiae strain with a conditional allele of ACC1, the essential acetyl-CoA carboxylase (ACC) gene, as a tool to test heterologous genes for complementation. Yarrowia lipolytica is an oleaginous yeast with a higher capacity for lipid production than S. cerevisiae, possibly due to a higher capacity to produce malonyl-CoA. Measuring relative intracellular malonyl-CoA levels with an in-vivo biosensor confirmed that expression of Y. lipolytica ACC in S. cerevisiae leads to a higher accumulation of malonyl-CoA compared with overexpression of the native gene from an otherwise identical vector. The higher accumulation was generally accompanied by a decreased growth rate. Concomitant expression of both the homologous and heterologous ACC1 genes eliminated the growth defect, with a marginal reduction of malonyl-CoA accumulation.

Enhanced CO2 fixation and lipid production of Chlorella vulgaris through the carbonic anhydrase complex

Photosynthesis of C. vulgaris shows slow growth and low lipid production due to the low solubility of CO₂, and it is thus necessary to increase the dissolved inorganic carbon source to solve this problem. In this study, carbonic anhydrase (CA) was fused with dockerin to form a CA complex by cohesion-dockerin interaction. The CA complex was displayed on the surface of C. vulgaris by a cellulose binding module. The CA complex increased activity and stability compared to those of a single enzyme. Additionally, C. vulgaris showed an average of 1.6-fold rapid growth during log phase through the influence of the CA complex. The bicarbonate produced by the CA complex increased the lipid production about 1.7-fold (23.3%), compared to 13.6% for the control group. The present results suggest that the CA complex successfully enhances the CO₂ fixation, which should be an essential study for 4th generation biofuels.

Antisense RNA-Based Strategy for Enhancing Surfactin Production in Bacillus subtilis TS1726 via Overexpression of the Unconventional Biotin Carboxylase II To Enhance ACCase Activity

The antisense RNA (asRNA) strategy is commonly used to block protein expression and downregulate the contents of metabolites in several microorganisms. Here, we show that the asRNA strategy can also be used to block gfp expression in Bacillus subtilis TS1726, which could further be utilized in the identification of new genes and functions. Via application of this strategy, biotin carboxylase II encoded by yngH (GeneID 939474) was identified to play a more significant role in maintaining acetyl-CoA carboxylase (ACCase) activity and enhancing surfactin synthesis compared to those of other ACCase subunits. The yngH gene was then overexpressed in the engineered strain B. subtilis TS1726(yngH). The surfactin titer of TS1726(yngH) increased to 13.37 g/L in a flask culture, representing a 43% increase compared to that of parental strain TS1726. This strategy opens the door to achieving large-scale production and broad application of surfactin.

Engineered microbial host selection for value-added bioproducts from lignocellulose

Lignocellulose is a rich and sustainable globally available carbon source and is considered a prominent alternative raw material for producing biofuels and valuable chemical compounds. Enzymatic hydrolysis is one of the crucial steps of lignocellulose degradation. Cellulolytic and hemicellulolytic enzyme mixes produced by different microorganisms including filamentous fungi, yeasts and bacteria, are used to degrade the biomass to liberate monosaccharides and other compounds for fermentation or conversion to value-added products. During biomass pretreatment and degradation, toxic compounds are produced, and undesirable carbon catabolic repression (CCR) can occur. In order to solve this problem, microbial metabolic pathways and transcription factors involved have been investigated along with the application of protein engineering to optimize the biorefinery platform. Engineered Microorganisms have been used to produce specific enzymes to breakdown biomass polymers and metabolize sugars to produce ethanol as well other biochemical compounds. Protein engineering strategies have been used for modifying lignocellulolytic enzymes to overcome enzymatic limitations and improving both their production and functionality. Furthermore, promoters and transcription factors, which are key proteins in this process, are modified to promote microbial gene expression that allows a maximum performance of the hydrolytic enzymes for lignocellulosic degradation. The present review will present a critical discussion and highlight the aspects of the use of microorganisms to convert lignocellulose into value-added bioproduct as well combat the bottlenecks to make the biorefinery platform from lignocellulose attractive to the market.

Systems and Synthetic Biology Approaches to Engineer Fungi for Fine Chemical Production

Since the advent of systems and synthetic biology, many studies have sought to harness microbes as cell factories through genetic and metabolic engineering approaches. Yeast and filamentous fungi have been successfully harnessed to produce fine and high value-added chemical products. In this review, we present some of the most promising advances from recent years in the use of fungi for this purpose, focusing on the manipulation of fungal strains using systems and synthetic biology tools to improve metabolic flow and the flow of secondary metabolites by pathway redesign. We also review the roles of bioinformatics analysis and predictions in synthetic circuits, highlighting in silico systemic approaches to improve the efficiency of synthetic modules.