The Role of Hexokinase and Hexose Transporters in Preferential Use of Glucose over Fructose and Downstream Metabolic Pathways in the Yeast Yarrowia lipolytica

Research progress on biosynthesis of erythritol and multi-dimensional optimization of production strategies

Erythritol, as a new type of natural sweetener, has been widely used in food, medical, cosmetics, pharmaceutical and other fields due to its unique physical and chemical properties and physiological functions. In recent years, with the continuous development of strategies such as synthetic biology, metabolic engineering, omics-based systems biology and high-throughput screening technology, people's understanding of the erythritol biosynthesis pathway has gradually deepened, and microbial cell factories with independent modification capabilities have been successfully constructed. In this review, the cheap feedstocks for erythritol synthesis are introduced in detail, the environmental factors affecting the synthesis of erythritol and its regulatory mechanism are described, and the tools and strategies of metabolic engineering involved in erythritol synthesis are summarized. In addition, the study of erythritol derivatives is helpful in expanding its application field. Finally, the challenges that hinder the effective production of erythritol are discussed, which lay a foundation for the green, efficient and sustainable production of erythritol in the future and breaking through the bottleneck of production.

Virtually identical does not mean exactly identical: Discrepancy in energy metabolism between glucose and fructose fermentation influences the reproductive potential of yeast cells

The physiological efficiency of cells largely depends on the possibility of metabolic adaptations to changing conditions, especially on the availability of nutrients. Central carbon metabolism has an essential role in cellular function. In most cells is based on glucose, which is the primary energy source, provides the carbon skeleton for the biosynthesis of important cell macromolecules, and acts as a signaling molecule. The metabolic flux between pathways of carbon metabolism such as glycolysis, pentose phosphate pathway, and mitochondrial oxidative phosphorylation is dynamically adjusted by specific cellular economics responding to extracellular conditions and intracellular demands. Using Saccharomyces cerevisiae yeast cells and potentially similar fermentable carbon sources i.e. glucose and fructose we analyzed the parameters concerning the metabolic status of the cells and connected with them alteration in cell reproductive potential. Those parameters were related to the specific metabolic network: the hexose uptake - glycolysis and activity of the cAMP/PKA pathway - pentose phosphate pathway and biosynthetic capacities - the oxidative respiration and energy generation. The results showed that yeast cells growing in a fructose medium slightly increased metabolism redirection toward respiratory activity, which decreased pentose phosphate pathway activity and cellular biosynthetic capabilities. These differences between the fermentative metabolism of glucose and fructose, lead to long-term effects, manifested by changes in the maximum reproductive potential of cells.

Boosting Geranyl Diphosphate Synthesis for Linalool Production in Engineered Yarrowia lipolytica

Linalool is a pleasant-smelling monoterpenoid widely found in the essential oils of most flowers. Due to its biologically active properties, linalool has considerable commercial potential, especially in the food and perfume industries. In this study, the oleaginous yeast Yarrowia lipolytica was successfully engineered to produce linalool de novo. The (S)-linalool synthase (LIS) gene from Actinidia argute was overexpressed to convert geranyl diphosphate (GPP) into linalool. Flux was diverted from farnesyl diphosphate (FPP) synthesis to GPP by introducing a mutated copy of the native ERG20F88W-N119W gene, and CrGPPS gene from Catharanthus roseus on its own and as part of a fusion with LIS. Disruption of native diacylglycerol kinase enzyme, DGK1, by oligo-mediated CRISPR-Cas9 inactivation further increased linalool production. The resulting strain accumulated 109.6 mg/L of linalool during cultivation in shake flasks with sucrose as a carbon source. CrGPPS expression in Yarrowia lipolytica increased linalool accumulation more efficiently than the ERG20F88W-N119W expression, suggesting that the increase in linalool production was predominantly influenced by the level of GPP precursor supply.

Application of New Yarrowia lipolytica Transformants in Production of Citrates and Erythritol from Glycerol

Citric acid and erythritol are obtained on an industrial scale using biotechnological methods. Due to the growing market demand for these products, research is underway to improve the process economics by introducing new microorganisms, in particular of the species Yarrowia lipolytica. The aim of this study was to evaluate transformants of Y. lipolytica for growth and ability to overproduce citric acids and erythritol from glycerol. The transformants were constructed by overexpressing glycerol kinase, methylcitrate synthase and mitochondrial succinate-fumarate transporter in the mutant Wratislavia 1.31. Next, strains were assessed for biosynthesis of citrate (pH 5.5; nitrogen limitation) and erythritol (pH 3.0; high osmotic pressure) from glycerol. Regardless of culture conditions strains, 1.31.GUT1/6 and 1.31.GUT1/6.CIT1/3 exhibited high rates of substrate utilization. Under conditions favoring citrate biosynthesis, both strains produced several percent more citrates, accompanied by higher erythritol production compared to the parental strain. During erythritol biosynthesis, the strain 1.31.GUT1/6.CIT1/3.E34672g obtained as a result of co-expression of all three genes stood out, producing 84.0 g/L of erythritol with yield and productivity of 0.54 g/g and 0.72 g/Lh, respectively, which places it in the group of the highest-ranked producers of erythritol among Y. lipolytica species.

Soybean molasses increases subcutaneous fat deposition while reducing lipid oxidation in the meat of castrated lambs

This study aimed to evaluate the effect of including soybean molasses (SM) on performance, blood parameters, carcass traits, meat quality, fatty acid, and muscle (longissimus thoracis) transcriptomic profiles of castrated lambs. Twenty Dorper × Santa Inês lambs (20.06 ± 0.76 kg body weight [BW]) were assigned to a randomized block design, stratified by BW, with the following treatments: CON: 0 g/kg of SM and SM20: 200 g/kg of SM on dry matter basis, allocated in individual pens. The diet consisted of 840 g/kg concentrate and 160 g/kg corn silage for 76 d, with the first 12 d as an adaptation period and the remaining 64 d on the finishing diet. The SM20 diet increased blood urea concentration (P = 0.03) while reduced glucose concentration (P = 0.04). Lambs fed SM showed higher subcutaneous fat deposition (P = 0.04) and higher subcutaneous adipocyte diameter (P < 0.01), in addition to reduced meat lipid oxidation (P < 0.01). SM reduced the quantity of branched-chain fatty acids in longissimus thoracis (P = 0.05) and increased the quantity of saturated fatty acids (P = 0.01). In the transcriptomic analysis, 294 genes were identified as differentially expressed, which belong to pathways such as oxidative phosphorylation, citric acid cycle, and monosaccharide metabolic process. In conclusion, diet with SM increased carcass fat deposition, reduced lipid oxidation, and changed the energy metabolism, supporting its use in ruminant nutrition.

Recent advances in biosynthesis mechanisms and yield enhancement strategies of erythritol

Erythritol is a four-carbon sugar alcohol naturally produced by microorganisms as an osmoprotectant. As a new sugar substitute, erythritol has recently been popular on the ingredient market because of its unique nutritional characteristics. Even though the history of erythritol biosynthesis dates from the turn of the twentieth century, scientific advancement has lagged behind other polyols due to the relative complexity of making it. In recent years, biosynthetic methods for erythritol have been rapidly developed due to an increase in market demand, a better understanding of metabolic pathways, and the rapid development of genetic engineering tools. This paper reviews the history of industrial strain development and focuses on the underlying mechanism of high erythritol production by strains gained through screening or mutagenesis. Meanwhile, we highlight the metabolic pathway knowledge of erythritol biosynthesis in microorganisms and summarize the metabolic engineering and research progress on critical genes involved in different stages of the synthetic pathway. Lastly, we talk about the still-contentious issues and promising future research directions that will help break the erythritol production bottleneck and make erythritol production greener and more sustainable.

Concomitant Production of Erythritol and β-Carotene by Engineered Yarrowia lipolytica

While the expansion of the erythritol production industry has resulted in unprecedented production of yeast cells, it also suffers from a lack of effective utilization. β-Carotene is a value-added compound that can be synthesized by engineered Yarrowia lipolytica. Here, we first evaluated the production performance of erythritol-producing yeast strains under two different morphologies and then successfully constructed a chassis with yeast-like morphology by deleting Mhy1 and Cla4 genes. Subsequently, β-carotene synthesis pathway genes, CarRA and CarB from Blakeslea trispora, were introduced to construct the β-carotene and erythritol coproducing Y. lipolytica strain ylmcc. The rate-limiting genes GGS1 and tHMG1 were overexpressed to increase the β-carotene yield by 45.32-fold compared with the strain ylmcc. However, increased β-carotene accumulation led to prolonged fermentation time; therefore, transporter engineering through overexpression of YTH1 and YTH3 genes was used to alleviate fermentation delays. Using batch fermentation in a 3 L bioreactor, this engineered Y. lipolytica strain produced erythritol with production, yield, and productivity values of 171 g/L, 0.56 g/g glucose, and 2.38 g/(L·h), respectively, with a concomitant β-carotene yield of 47.36 ± 0.06 mg/g DCW. The approach presented here improves the value of erythritol-producing cells and offers a low-cost technique to obtain hydrophobic terpenoids.