Biosynthesis of insect sex pheromone precursors via engineered ß-oxidation in yeast.

Mating disruption with insect sex pheromones is an attractive and environmentally friendly technique for pest management. Several Lepidoptera sex pheromones have been produced in yeast, where biosynthesis could be accomplished by the expression of fatty acyl-CoA desaturases and fatty acyl-CoA reductases. In this study, we aimed to develop yeast Yarrowia lipolytica cell factories for producing Lepidoptera pheromones which biosynthesis additionally requires ß-oxidation, such as (Z)-7-dodecenol (Z7-12:OH), (Z)-9-dodecenol (Z9-12:OH), and (Z)-7-tetradecenol (Z7-14:OH). We expressed fatty acyl-CoA desaturases from Drosophila melanogaster (Dmd9) or Lobesia botrana (Lbo_PPTQ) and fatty acyl-CoA reductase from Helicoverpa armigera (HarFAR) in combinations with 11 peroxisomal oxidases of different origins. Yeast cultivations were performed with supplementation of methyl myristate (14:Me). The oxidase Lbo_31670 from L. botrana provided the highest titers of (Z)-7-dodecenoate, (Z)-9-dodecenoate, and (Z)-7-tetradecenoate. However, no chain-shortened fatty alcohols were produced. The mutation of fatty acid synthase (Fas2pI1220F) to increase myristate production did not lead to targeted fatty alcohol production. The problem was solved by directing the reductase into peroxisomes, where the strain with Dmd9 produced 0.10 ± 0.02 mg/l of Z7-12:OH and 0.48 ± 0.03 mg/l of Z7-14:OH, while the strain with Lbo_PPTQ produced 0.21 ± 0.03 mg/l of Z9-12:OH and 0.40 ± 0.07 mg/l of Z7-14:OH. In summary, the engineering of ß-oxidation in Y. lipolytica allowed expanding the portfolio of microbially produced insect sex pheromones.

Tailored biosynthesis of gibberellin plant hormones in yeast.

The application of small amounts of natural plant growth hormones, such as gibberellins (GAs), can increase the productivity and quality of many vegetable and fruit crops. However, gibberellin growth hormones usage is limited by the high cost of their production, which is currently based on fermentation of a natural fungal producer Fusarium fujikuroi that produces a mix of several GAs. We explored the potential of the oleaginous yeast Yarrowia lipolytica to produce specific profiles of GAs. Firstly, the production of the GA-precursor ent-kaurenoic acid (KA) at 3.75 mg/L was achieved by expression of biosynthetic enzymes from the plant Arabidopsis thaliana and upregulation of the mevalonate (MVA) pathway. We then built a GA4-producing strain by extending the GA-biosynthetic pathway and upregulating the MVA-pathway further, resulting in 17.29 mg/L GA4. Additional expression of the F. fujikoroi GA-biosynthetic enzymes resulted in the production of GA7 (trace amounts) and GA3 (2.93 mg/L). Lastly, through protein engineering and the expression of additional KA-biosynthetic genes, we increased the GA3-production 4.4-fold resulting in 12.81 mg/L. The developed system presents a promising resource for the recombinant production of specific gibberellins, identifying bottlenecks in GA biosynthesis, and discovering new GA biosynthetic genes. CLASSIFICATION: Biological Sciences, Applied Biological Sciences.

Glucose-Dependent Promoters for Dynamic Regulation of Metabolic Pathways.

For an industrial fermentation process, it can be advantageous to decouple cell growth from product formation. This decoupling would allow for the rapid accumulation of biomass without inhibition from product formation, after which the fermentation can be switched to a mode where cells would grow minimally and primarily act as catalysts to convert substrate into desired product. The switch in fermentation mode should preferably be accomplished without the addition of expensive inducers. A common cell factory Saccharomyces cerevisiae is a Crabtree-positive yeast and is typically fermented at industrial scale under glucose-limited conditions to avoid the formation of ethanol. In this work, we aimed to identify and characterize promoters that depend on glucose concentration for use as dynamic control elements. Through analysis of mRNA data of S. cerevisiae grown in chemostats under glucose excess or limitation, we identified 34 candidate promoters that strongly responded to glucose presence or absence. These promoters were characterized in small-scale batch and fed-batch cultivations using a quickly maturing rapidly degrading green fluorescent protein yEGFP3-Cln2PEST as a reporter. Expressing 3-hydroxypropionic acid (3HP) pathway from a set of selected regulated promoters allowed for suppression of 3HP production during glucose-excess phase of a batch cultivation with subsequent activation in glucose-limiting conditions. Regulating the 3HP pathway by the ICL1 promoter resulted in 70% improvement of 3HP titer in comparison to PGK1 promoter.

EasyCloneYALI: CRISPR/Cas9-Based Synthetic Toolbox for Engineering of the Yeast Yarrowia lipolytica.

The oleaginous yeast Yarrowia lipolytica is an emerging host for production of fatty acid-derived chemicals. To enable rapid iterative metabolic engineering of this yeast, there is a need for well-characterized genetic parts and convenient and reliable methods for their incorporation into yeast. Here, the EasyCloneYALI genetic toolbox, which allows streamlined strain construction with high genome editing efficiencies in Y. lipolytica via the CRISPR/Cas9 technology is presented. The toolbox allows marker-free integration of gene expression vectors into characterized genome sites as well as marker-free deletion of genes with the help of CRISPR/Cas9. Genome editing efficiencies above 80% were achieved with transformation protocols using non-replicating DNA repair fragments (such as DNA oligos). Furthermore, the toolbox includes a set of integrative gene expression vectors with prototrophic markers conferring resistance to hygromycin and nourseothricin.

Engineering prokaryotic transcriptional activators as metabolite biosensors in yeast.

Whole-cell biocatalysts have proven a tractable path toward sustainable production of bulk and fine chemicals. Yet the screening of libraries of cellular designs to identify best-performing biocatalysts is most often a low-throughput endeavor. For this reason, the development of biosensors enabling real-time monitoring of production has attracted attention. Here we applied systematic engineering of multiple parameters to search for a general biosensor design in the budding yeast Saccharomyces cerevisiae based on small-molecule binding transcriptional activators from the prokaryote superfamily of LysR-type transcriptional regulators (LTTRs). We identified a design supporting LTTR-dependent activation of reporter gene expression in the presence of cognate small-molecule inducers. As proof of principle, we applied the biosensors for in vivo screening of cells producing naringenin or cis,cis-muconic acid at different levels, and found that reporter gene output correlated with production. The transplantation of prokaryotic transcriptional activators into the eukaryotic chassis illustrates the potential of a hitherto untapped biosensor resource useful for biotechnological applications.

EasyCloneMulti: A Set of Vectors for Simultaneous and Multiple Genomic Integrations in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is widely used in the biotechnology industry for production of ethanol, recombinant proteins, food ingredients and other chemicals. In order to generate highly producing and stable strains, genome integration of genes encoding metabolic pathway enzymes is the preferred option. However, integration of pathway genes in single or few copies, especially those encoding rate-controlling steps, is often not sufficient to sustain high metabolic fluxes. By exploiting the sequence diversity in the long terminal repeats (LTR) of Ty retrotransposons, we developed a new set of integrative vectors, EasyCloneMulti, that enables multiple and simultaneous integration of genes in S. cerevisiae. By creating vector backbones that combine consensus sequences that aim at targeting subsets of Ty sequences and a quickly degrading selective marker, integrations at multiple genomic loci and a range of expression levels were obtained, as assessed with the green fluorescent protein (GFP) reporter system. The EasyCloneMulti vector set was applied to balance the expression of the rate-controlling step in the ß-alanine pathway for biosynthesis of 3-hydroxypropionic acid (3HP). The best 3HP producing clone, with 5.45 g.L(-1) of 3HP, produced 11 times more 3HP than the lowest producing clone, which demonstrates the capability of EasyCloneMulti vectors to impact metabolic pathway enzyme activity.

Engineering and systems-level analysis of Saccharomyces cerevisiae for production of 3-hydroxypropionic acid via malonyl-CoA reductase-dependent pathway.

BACKGROUND: In the future, oil- and gas-derived polymers may be replaced with bio-based polymers, produced from renewable feedstocks using engineered cell factories. Acrylic acid and acrylic esters with an estimated world annual production of approximately 6 million tons by 2017 can be derived from 3-hydroxypropionic acid (3HP), which can be produced by microbial fermentation. For an economically viable process 3HP must be produced at high titer, rate and yield and preferably at low pH to minimize downstream processing costs. RESULTS: Here we describe the metabolic engineering of baker's yeast Saccharomyces cerevisiae for biosynthesis of 3HP via a malonyl-CoA reductase (MCR)-dependent pathway. Integration of multiple copies of MCR from Chloroflexus aurantiacus and of phosphorylation-deficient acetyl-CoA carboxylase ACC1 genes into the genome of yeast increased 3HP titer fivefold in comparison with single integration. Furthermore we optimized the supply of acetyl-CoA by overexpressing native pyruvate decarboxylase PDC1, aldehyde dehydrogenase ALD6, and acetyl-CoA synthase from Salmonella enterica SEacs (L641P). Finally we engineered the cofactor specificity of the glyceraldehyde-3-phosphate dehydrogenase to increase the intracellular production of NADPH at the expense of NADH and thus improve 3HP production and reduce formation of glycerol as by-product. The final strain produced 9.8 ± 0.4 g L(-1) 3HP with a yield of 13% C-mol C-mol(-1) glucose after 100 h in carbon-limited fed-batch cultivation at pH 5. The 3HP-producing strain was characterized by (13)C metabolic flux analysis and by transcriptome analysis, which revealed some unexpected consequences of the undertaken metabolic engineering strategy, and based on this data, future metabolic engineering directions are proposed. CONCLUSIONS: In this study, S. cerevisiae was engineered for high-level production of 3HP by increasing the copy numbers of biosynthetic genes and improving flux towards precursors and redox cofactors. This strain represents a good platform for further optimization of 3HP production and hence an important step towards potential commercial bio-based production of 3HP.

De novo production of resveratrol from glucose or ethanol by engineered Saccharomyces cerevisiae.

Resveratrol is a natural antioxidant compound, used as food supplement and cosmetic ingredient. Microbial production of resveratrol has until now been achieved by supplementation of expensive substrates, p-coumaric acid or aromatic amino acids. Here we engineered the yeast Saccharomyces cerevisiae to produce resveratrol directly from glucose or ethanol via tyrosine intermediate. First we introduced the biosynthetic pathway, consisting of tyrosine ammonia-lyase from Herpetosiphon aurantiacus, 4-coumaryl-CoA ligase from Arabidopsis thaliana and resveratrol synthase from Vitis vinifera, and obtained 2.73 ± 0.05 mg L(-1) resveratrol from glucose. Then we over-expressed feedback-insensitive alleles of ARO4 encoding 3-deoxy-D-arabino-heptulosonate-7-phosphate and ARO7 encoding chorismate mutase, resulting in production of 4.85 ± 0.31 mg L(-1) resveratrol from glucose as the sole carbon source. Next we improved the supply of the precursor malonyl-CoA by over-expressing a post-translational de-regulated version of the acetyl-CoA carboxylase encoding gene ACC1; this strategy further increased resveratrol production to 6.39 ± 0.03 mg L(-1). Subsequently, we improved the strain by performing multiple-integration of pathway genes resulting in resveratrol production of 235.57 ± 7.00 mg L(-1). Finally, fed-batch fermentation of the final strain with glucose or ethanol as carbon source resulted in a resveratrol titer of 415.65 and 531.41 mg L(-1), respectively.

Establishment of a yeast platform strain for production of p-coumaric acid through metabolic engineering of aromatic amino acid biosynthesis.

Aromatic amino acids are precursors of numerous plant secondary metabolites with diverse biological functions. Many of these secondary metabolites are already being used as active pharmaceutical or nutraceutical ingredients, and there are numerous exploratory studies of other compounds with promising applications. p-Coumaric acid is derived from aromatic amino acids and, besides being a valuable chemical building block, it serves as precursor for biosynthesis of many secondary metabolites, such as polyphenols, flavonoids, and some polyketides. Here we developed a p-coumaric acid-overproducing Saccharomyces cerevisiae platform strain. First, we reduced by-product formation by knocking out phenylpyruvate decarboxylase ARO10 and pyruvate decarboxylase PDC5. Second, different versions of feedback-resistant DAHP synthase and chorismate mutase were overexpressed. Finally, we identified shikimate kinase as another important flux-controlling step in the aromatic amino acid pathway by overexpressing enzymes from Escherichia coli, homologous to the pentafunctional enzyme Aro1p and to the bifunctional chorismate synthase-flavin reductase Aro2p. The highest titer of p-coumaric acid of 1.93 ± 0.26 g L(-1) was obtained, when overexpressing tyrosine ammonia-lyase TAL from Flavobacterium johnsoniaeu, DAHP synthase ARO4(K229L), chorismate mutase ARO7(G141S) and E. coli shikimate kinase II (aroL) in Δpdc5Δaro10 strain background. To our knowledge this is the highest reported titer of an aromatic compound produced by yeast. The developed S. cerevisiae strain represents an attractive platform host for production of p-coumaric-acid derived secondary metabolites, such as flavonoids, polyphenols, and polyketides.

Establishing a synthetic pathway for high-level production of 3-hydroxypropionic acid in Saccharomyces cerevisiae via ß-alanine.

Microbial fermentation of renewable feedstocks into plastic monomers can decrease our fossil dependence and reduce global CO2 emissions. 3-Hydroxypropionic acid (3HP) is a potential chemical building block for sustainable production of superabsorbent polymers and acrylic plastics. With the objective of developing Saccharomyces cerevisiae as an efficient cell factory for high-level production of 3HP, we identified the ß-alanine biosynthetic route as the most economically attractive according to the metabolic modeling. We engineered and optimized a synthetic pathway for de novo biosynthesis of ß-alanine and its subsequent conversion into 3HP using a novel ß-alanine-pyruvate aminotransferase discovered in Bacillus cereus. The final strain produced 3HP at a titer of 13.7±0.3gL(-1) with a 0.14±0.0C-molC-mol(-1) yield on glucose in 80h in controlled fed-batch fermentation in mineral medium at pH 5, and this work therefore lays the basis for developing a process for biological 3HP production.

Production of 3-hydroxypropionic acid from glucose and xylose by metabolically engineered Saccharomyces cerevisiae.

Biomass, the most abundant carbon source on the planet, may in the future become the primary feedstock for production of fuels and chemicals, replacing fossil feedstocks. This will, however, require development of cell factories that can convert both C6 and C5 sugars present in lignocellulosic biomass into the products of interest. We engineered Saccharomyces cerevisiae for production of 3-hydroxypropionic acid (3HP), a potential building block for acrylates, from glucose and xylose. We introduced the 3HP biosynthetic pathways via malonyl-CoA or ß-alanine intermediates into a xylose-consuming yeast. Using controlled fed-batch cultivation, we obtained 7.37±0.17 g 3HP L-1 in 120 hours with an overall yield of 29±1% Cmol 3HP Cmol-1 xylose. This study is the first demonstration of the potential of using S. cerevisiae for production of 3HP from the biomass sugar xylose.

Evolution reveals a glutathione-dependent mechanism of 3-hydroxypropionic acid tolerance.

Biologically produced 3-hydroxypropionic acid (3 HP) is a potential source for sustainable acrylates and can also find direct use as monomer in the production of biodegradable polymers. For industrial-scale production there is a need for robust cell factories tolerant to high concentration of 3 HP, preferably at low pH. Through adaptive laboratory evolution we selected S. cerevisiae strains with improved tolerance to 3 HP at pH 3.5. Genome sequencing followed by functional analysis identified the causal mutation in SFA1 gene encoding S-(hydroxymethyl)glutathione dehydrogenase. Based on our findings, we propose that 3 HP toxicity is mediated by 3-hydroxypropionic aldehyde (reuterin) and that glutathione-dependent reactions are used for reuterin detoxification. The identified molecular response to 3 HP and reuterin may well be a general mechanism for handling resistance to organic acid and aldehydes by living cells.

EasyClone: method for iterative chromosomal integration of multiple genes in Saccharomyces cerevisiae.

Development of strains for efficient production of chemicals and pharmaceuticals requires multiple rounds of genetic engineering. In this study, we describe construction and characterization of EasyClone vector set for baker's yeast Saccharomyces cerevisiae, which enables simultaneous expression of multiple genes with an option of recycling selection markers. The vectors combine the advantage of efficient uracil excision reaction-based cloning and Cre-LoxP-mediated marker recycling system. The episomal and integrative vector sets were tested by inserting genes encoding cyan, yellow, and red fluorescent proteins into separate vectors and analyzing for co-expression of proteins by flow cytometry. Cells expressing genes encoding for the three fluorescent proteins from three integrations exhibited a much higher level of simultaneous expression than cells producing fluorescent proteins encoded on episomal plasmids, where correspondingly 95% and 6% of the cells were within a fluorescence interval of Log10 mean ± 15% for all three colors. We demonstrate that selective markers can be simultaneously removed using Cre-mediated recombination and all the integrated heterologous genes remain in the chromosome and show unchanged expression levels. Hence, this system is suitable for metabolic engineering in yeast where multiple rounds of gene introduction and marker recycling can be carried out.