Evolutionary Engineering Improved d-Glucose/Xylose Cofermentation of Yarrowia lipolytica

Engineering Xylose Isomerase and Reductase Pathways in Yarrowia lipolytica for Efficient Lipid Production

Xylose is a common monosaccharide in lignocellulosic residues that Yarrowia lipolytica cannot naturally metabolise for lipid production and therefore, heterologous xylose metabolic pathways must be engineered in this yeast to facilitate its consumption. We have compared the metabolic efficiency of two xylose metabolic pathways by developing three recombinant Y. lipolytica strains: one harbouring a xylose reductase pathway, one with a xylose isomerase pathway, and one combining both pathways, and the strains were tested for xylose consumption and lipid production at different scales. The recombinant strain with the reductase pathway that was directly isolated in selective xylose medium showed the highest lipid yield, producing up to 12.8 g/L of lipids, or 43% of the biomass dry weight, without requiring any other xylose consumption adaptive evolution process. This strain achieved a lipid yield of 0.13 g lipids/g xylose, one of the highest yields in yeast reported so far using xylose as the sole carbon and energy source. Although the strain harbouring the isomerase pathway performed better under oxygen-limiting conditions and led to higher lipid intracellular accumulation, it showed a lower xylose uptake and biomass production, rendering a lower yield under non-limiting oxygen conditions. Unexpectedly, the combination of both pathways in the same strain was less effective than the use of the reductase pathway alone.

Characterization of cotton stalk as a lignocellulosic feedstock for single-cell protein production

Cotton stalk, an important by-product of cotton farming, is challenging in lignocellulosic feedstock application due to the limited understanding of their compositional and lignin structural characteristics. This study elucidates the composition of lignocellulose components and fundamental lignin structural features of cotton stalk. Lignocellulosic hydrolysates were prepared from various cotton stalk parts and used for single-cell protein production. As a proof of concept, cotton stalk hydrolysates were successfully converted into single-cell protein using the superior microbial host, Candida utilis ACCC20060, owing to its favorable sugar consumption efficiency and high protein quality. The highest SCP concentration of 5.74 g/L was obtained, yielding 0.23 g/g from the lignocellulose-derived sugars released from cotton stalk roots. This study provides valuable references for cotton stalk utilization toward lignocellulosic feedstock application and introduces a promising microbial host for single-cell protein production from such feedstocks.

Toward rapid and efficient utilization of nonconventional substrates by nonconventional yeast strains

Economic and sustainable production of biofuels and chemicals necessitates utilizing abundant and inexpensive lignocellulosic biomass. Yet, Saccharomyces cerevisiae, a workhorse strain for industrial biotechnology based on starch and sugarcane-derived sugars, is not suitable for lignocellulosic bioconversion due to a lack of pentose metabolic pathways and severe inhibition by toxic inhibitors in cellulosic hydrolysates. This review underscores the potential of nonconventional yeast strains, specifically Yarrowia lipolytica and Rhodotorula toruloides, for converting underutilized carbon sources, such as xylose and acetate, into high-value products. Multi-omics studies with nonconventional yeast have elucidated the structure and regulation of metabolic pathways for efficient and rapid utilization of xylose and acetate. The review delves into the advantages of using xylose and acetate for producing biofuels and chemicals. Collectively, value-added biotransformation of nonconventional substrates by nonconventional yeast strains is a promising strategy to improve both economics and sustainability of bioproduction.

Efficient production of mycosporine-like amino acids, natural sunscreens, in Yarrowia lipolytica

BACKGROUND

Mycosporine-like amino acids (MAAs), including shinorine and porphyra-334, are gaining attention as safe natural sunscreens. The production of MAAs has been achieved in diverse microbial hosts, including Saccharomyces cerevisiae. While S. cerevisiae is the most extensively studied model yeast, the oleaginous yeast Yarrowia lipolytica has emerged as a promising candidate for the synthesis of valuable products. In this study, we explored the potential of Y. lipolytica as a host for producing MAAs, utilizing its advantages such as a robust pentose phosphate pathway flux and versatile carbon source utilization.

RESULTS

We produced MAAs in Y. lipolytica by introducing the MAA biosynthetic genes from cyanobacteria Nostoc punctiforme and Anabaena variabilis. These genes include mysA, mysB, and mysC responsible for producing mycosporine-glycine (MG) from sedoheptulose 7-phosphate (S7P). The two strains utilize different enzymes, D-Ala-D-Ala ligase homologue (MysD) in N. punctiforme and NRPS-like enzyme (MysE) in A. variabilis, for amino acid conjugation to MG. MysE specifically generated shinorine, a serine conjugate of MG, while MysD exhibited substrate promiscuity, yielding both shinorine and a small amount of porphyra-334, a threonine conjugate of MG. We enhanced MAAs production by selecting mysA, mysB, and mysC from A. variabilis and mysD from N. punctiforme based on their activities. We further improved production by strengthening promoters, increasing gene copies, and introducing the xylose utilization pathway. Co-utilization of xylose with glucose or glycerol increased MAAs production by boosting the S7P pool through the pentose phosphate pathway. Overexpressing GND1 and ZWF1, key genes in the pentose phosphate pathway, further enhanced MAAs production. The highest achieved MAAs level was 249.0 mg/L (207.4 mg/L shinorine and 41.6 mg/L of porphyra-334) in YP medium containing 10 g/L glucose and 10 g/L xylose.

CONCLUSIONS

Y. lipolytica was successfully engineered to produce MAAs, primarily shinorine. This achievement involved the introduction of MAA biosynthetic genes from cyanobacteria, establishing xylose utilizing pathway, and overexpressing the pentose phosphate pathway genes. These results highlight the potential of Y. lipolytica as a promising yeast chassis strain for MAAs production, notably attributed to its proficient expression of MysE enzyme, which remains non-functional in S. cerevisiae, and versatile utilization of carbon sources like glycerol.

Application of adaptive laboratory evolution for Yarrowia lipolytica: A comprehensive review

Adaptive laboratory evolution is an innovative approach utilized by researchers to enhance the characteristics of microorganisms in the field of biology. With the advancement of this technology, it is now being extended to non-model strains. Yarrowia lipolytica, an oleaginous yeast with significant industrial potential, stands out among the non-conventional fungi. However, the activity of Yarrowia lipolytica is frequently affected by specific substances and environmental factors, necessitating the development of techniques to address these challenges. This manuscript provides an overview of adaptive laboratory evolution experiments conducted on Yarrowia lipolytica, and categorizes the contents into two aspects including improving lignocellulose utilization and enhancing the production in Yarrowia lipolytica. Additionally, we selected several representative examples to illustrate how adaptive laboratory evolution can be combined with other techniques to elucidate the potential mechanisms underlying strain evolution. Lastly, we anticipate a promising future for adaptive laboratory evolution technology and Yarrowia lipolytica in tandem.

Construction of prokaryotic nanocompartment in Yarrowia lipolytica to assist phloroglucinol production

Phloroglucinol is an important chemical intermediate which has been tentatively produced by engineered bacteria. However, its biosynthesis in industry is limited due to its natural antibacterial activity. Our study firstly selected Yarrowia lipolytica as the chassis strain, which was verified to be tolerable to phloroglucinol. Then the gene of type III polyketone synthase PhlD (the key biosynthetic gene) was overexpressed to facilitate phloroglucinol production with a concentration of 107.4 mg/L. Furthermore, we introduced the prokaryotic nanocompartment to assist the intracellular catalytic activity. The results showed that the concentration of phloroglucinol was increased by about 2.5 times, indicating this multifunctional nanocompartment is orthogonal to the physiological activities of Y. lipolytica. Additionally, fermentations with xylose and lignocellulosic hydrolysates as the carbon source were performed with the engineered Y. lipolytica, resulting in a total concentration of 580.2 mg/L and 328.9 mg/L, respectively. These findings revealed the potential of Y. lipolytica in phloroglucinol production and provided an effective nanocompartment strategy to improve the catalytic activity of the enzyme for boosting phloroglucinol production. KEY POINTS: • The first time to select and use Y. lipolytica to produce phloroglucinol. • Successful construction of prokaryotic nanocompartment in Y. lipolytica to increase production of phloroglucinol. • Lignocellulose hydrolysate is used as a substrate in fermentation.

Adaptive laboratory evolution boost Yarrowia lipolytica tolerance to vanillic acid

Microbial tolerance to lignocellulose-derived inhibitors, such as aromatic acids, is critical for the economical production of biofuels and biochemicals. Here, adaptive laboratory evolution was applied to improve the tolerance of Yarrowia lipolytica to a representative aromatic acid inhibitor vanillic acid. The transcriptome profiling of evolved strain suggested that the tolerance could be related to the up-regulation of RNA processing and multidrug transporting pathways. Further analysis by reverse engineering confirmed that the amplification of YALI0_F13475g coding for transcriptional coactivator and YALI0_E25201g coding for multidrug transporter conferred tolerance not only to vanillic acid but also towards ferulic acid, p-coumaric acid, p-hydroxybenzoic acid and syringic acid. These findings suggested that regulation of RNA processing and multidrug transporting pathways may be important for enhanced aromatic acid tolerance in Y. lipolytica. This study provides valuable genetic information for robust strain construction for lignocellulosic biorefinery.

Efficient production of the β-ionone aroma compound from organic waste hydrolysates using an engineered Yarrowia lipolytica strain

This study demonstrates the feasibility of establishing a natural compound supply chain in a biorefinery. The process starts with the biological or chemical hydrolysis of food and agricultural waste into simple and fermentative sugars, followed by their fermentation into more complex molecules. The yeast strain, Yarrowia lipolytica, was modified by introducing high membrane affinity variants of the carotenoid cleavage dioxygenase enzyme, PhCCD1, to increase the production of the aroma compound, β-ionone. The initial hydrolysis process converted food waste or sugarcane bagasse into nutrient-rich hydrolysates containing 78.4 g/L glucose and 8.3 g/L fructose, or 34.7 g/L glucose and 20.1 g/L xylose, respectively. During the next step, engineered Y. lipolytica strains were used to produce β-ionone from these feedstocks. The yeast strain YLBI3120, carrying a modified PhCCD1 gene was able to produce 4 g/L of β-ionone with a productivity of 13.9 mg/L/h from food waste hydrolysate. This is the highest yield reported for the fermentation of this compound to date. The integrated process described in this study could be scaled up to achieve economical large-scale conversion of inedible food and agricultural waste into valuable aroma compounds for a wide range of potential applications.

Engineering Yarrowia lipolytica to produce fuels and chemicals from xylose: A review

The production of chemicals and fuels from lignocellulosic biomass has great potential industrial applications due to its economic feasibility and environmental attractiveness. However, the utilized microorganisms must be able to use all the sugars present in lignocellulosic hydrolysates, especially xylose, the second most plentiful monosaccharide on earth. Yarrowia lipolytica is a good candidate for producing various valuable products from biomass, but this yeast is unable to catabolize xylose efficiently. The development of metabolic engineering facilitated the application of Y. lipolytica as a platform for the bioconversion of xylose into various value-added products. Here, we reviewed the research progress on natural xylose-utilization pathways and their reconstruction in Y. lipolytica. The progress and emerging trends in metabolic engineering of Y. lipolytica for producing chemicals and fuels are further introduced. Finally, challenges and future perspectives of using lignocellulosic hydrolysate as substrate for Y. lipolytica are discussed.

Combined adaptive evolution and transcriptomic profiles reveal aromatic aldehydes tolerance mechanisms in Yarrowia lipolytica

Yarrowia lipolytica is an efficient oleaginous yeast, whereas its activity is typically reduced by inhibitors present in lignocellulosic hydrolysate. Understanding the response mechanism of Y. lipolytica to hydrolysate inhibitors and developing inhibitor tolerant strains are vital to lignocellulose valorization by this promising species. In this study, through adaptive laboratory evolution on three representative aromatic aldehyde inhibitors, evolved strains were obtained. Fermentation phenotype suggested that aromatic aldehydes conversion was one main reason for high tolerance of adapted strains. Transcriptome profiling analysis and reverse metabolic engineering confirmed that overexpressing the aldehyde ketone reductase gene YALI0_B07117g and aldehyde dehydrogenase gene YALI0_B01298g effectively converted aromatic aldehyde to corresponding alcohols and acids. The potential degradation pathways for aromatic aldehyde inhibitors in Y. lipolytica XYL+ were then discussed. This study provided insights to the aromatic aldehyde degradation in Y. lipolytica and a reliable basis for the development of aromatic aldehyde tolerant strains.

Adaptive laboratory evolution of Yarrowia lipolytica improves ferulic acid tolerance

Yarrowia lipolytica strain is a promising cell factory for the conversion of lignocellulose to biofuels and bioproducts. Despite the inherent robustness of this strain, further improvements to lignocellulose-derived inhibitors toxicity tolerance of Y. lipolytica are also required to achieve industrial application. Here, adaptive laboratory evolution was employed with increasing concentrations of ferulic acid. The adaptive laboratory evolution experiments led to evolve Y. lipolytica strain yl-XYL + *FA*4 with increased tolerance to ferulic acid as compared to the parental strain. Specifically, the evolved strain could tolerate 1.5 g/L ferulic acid, whereas 0.5 g/L ferulic acid could cause about 90% lethality of the parental strain. Transcriptome analysis of the evolved strain revealed several targets underlying toxicity tolerance enhancements. YALI0_E25201g, YALI0_F05984g, YALI0_B18854g, and YALI0_F16731g were among the highest upregulated genes, and the beneficial contributions of these genes were verified via reverse engineering. Recombinant strains with overexpressing each of these four genes obtained enhanced tolerance to ferulic acid as compared to the control strain. Fortunately, recombinant strains with overexpression of YALI0_E25201g, YALI0_B18854g, and YALI0_F16731g individually also obtained enhanced tolerance to vanillic acid. Overall, this work demonstrated a whole strain improvement cycle by "non-rational" metabolic engineering and presented new targets to modify Y. lipolytica for microbial lignocellulose valorization. KEY POINTS: • Adaptive evolution improved the ferulic acid tolerance of Yarrowia lipolytica • Transcriptome sequence was applied to analyze the ferulic acid tolerate strain • Three genes were demonstrated for both ferulic acid and vanillic acid tolerance.