Heterologous Mevalonate Production inStreptomyces lividansTK23

Metabolic engineering of Halomonas bluephagenesis for high-level mevalonate production from glucose and acetate mixture

Mevalonate (MVA) plays a crucial role as a building block for the biosynthesis of isoprenoids. In this study, we engineered Halomonas bluephagenesis to efficiently produce MVA. Firstly, by screening MVA synthetases from eight different species, the two efficient candidate modules, specifically NADPH-dependent mvaESEfa from Enterococcus faecalis and NADH-dependent mvaESLca from Lactobacillus casei, were integrated into the chromosome, leading to the construction of the H. bluephagenesis MVA11. Through the synergetic utilization of glucose and acetate as mixed carbon sources, MVA11 produced 11.2 g/L MVA with a yield of 0.45 g/g (glucose + acetic acid) in the shake flask. Subsequently, 10 beneficial genes out of 50 targets that could promote MVA production were identified using CRISPR interference. The simultaneous repression of rpoN (encoding RNA polymerase sigma-54 factor) and IldD (encoding L-lactate dehydrogenase) increased MVA titer (13.3 g/L) by 19.23% and yield (0.53 g/g (glucose + acetic acid)) by 17.78%, respectively. Furthermore, introducing the non-oxidative glycolysis (NOG) pathway into MVA11 enhanced MVA yield by 12.20%. Ultimately, by combining these strategies, the resultant H. bluephagenesis MVA13/pli-63 produced 13.9 g/L MVA in the shake flask, and the yield increased to 0.56 g/g (glucose + acetic acid), which was the highest reported so far. Under open fed-batch fermentation conditions, H. bluephagenesis MVA13/pli-63 produced 121 g/L of MVA with a yield of 0.42 g/g (glucose + acetic acid), representing the highest reported titer and yield in the bioreactor to date. This study demonstrates that H. bluephagenesis is one of the most favorable chassis for MVA production.

Microbial Production of Mevalonate

Mevalonate, an important intermediate product of the mevalonate pathway, has a broad spectrum of applications. With the rapid growth of metabolic engineering and synthetic biology, mevalonate biosynthesis by microorganisms is feasible and holds great promise in the future. In this review, we summarize the applications of mevalonate and its derivatives and describe the biosynthesis pathways of mevalonate. The current status of mevalonate biosynthesis is also detailed with an emphasis on metabolic engineering strategies to enhance mevalonate production in typical industrial organisms, including Escherichia coli, Saccharomyces cerevisiae, and Pseudomonas putida, suggesting new insights for the efficient production of biosynthesized mevalonate.

Wine Aroma Characterization of the Two Main Fermentation Yeast Species of the Apiculate Genus Hanseniaspora

Hanseniaspora species are the main yeasts isolated from grapes and grape musts. Regarding genetic and phenotypical characterization, especially fermentative behavior, they can be classified in two technological clusters: the fruit group and the fermentation group. Among the species belonging to the last group, Hanseniaspora osmophila and Hanseniaspora vineae have been previously isolated in spontaneous fermentations of grape must. In this work, the oenological aptitudes of the two species of the fermentation group were compared with Saccharomyces cerevisiae and the main species of the fruit group, Hanseniaspora uvarum. Both H. osmophila and H. vineae conferred a positive aroma to final wines and no sensory defects were detected. Wines fermented with H. vineae presented significantly higher concentrations of 2-phenylethyl, tryptophol and tyrosol acetates, acetoin, mevalonolactone, and benzyl alcohol compared to H. osmophila. Sensorial analysis showed increased intensity of fruity and flowery notes in wines vinificated with H. vineae. In an evolutionary context, the detoxification of alcohols through a highly acetylation capacity might explain an adaption to fermentative environments. It was concluded that, although H. vineae show close alcohol fermentation adaptations to H. osmophila, the increased activation of phenylpropanoid metabolic pathway is a particular characteristic of H. vineae within this important apiculate genus.

Metabolic impact of nutrient starvation in mevalonate-producing Escherichia coli

The aim of this work was to enhance mevalonate yield from glucose in Escherichia coli by essential nutrient starvations and to reveal these effects on the central carbon metabolism. Stationary phase culture without essential nutrients such as nitrogen, sulfur, and magnesium was evaluated using an engineered E. coli introducing mvaE and mvaS genes from Enterococcus faecalis. Sulfur starvation resulted in the highest mevalonate yield of 0.61C-molC-mol^-1 from glucose. The metabolic impacts of nutrient starvation were investigated by ¹³C-metabolic flux analysis. Under nitrogen starvation, the flux of the TCA cycle was large, causing high CO₂ production. This was caused by degradation of mevalonate synthesis pathway enzymes. Under magnesium starvation, NADPH production was decreased, which limited mevalonate synthesis and promoted an overflow of acetate. Sulfur starvation not only suppressed the TCA cycle flux, but also supplied NADPH for mevalonate synthesis.

13C-metabolic flux analysis for mevalonate-producing strain of Escherichia coli

Mevalonate (MVA) is used to produce various useful products such as drugs, cosmetics and food additives. An MVA-producing strain of Escherichia coli (engineered) was constructed by introducing mvaES genes from Enterococcus faecalis. The engineered strain produced 1.84 mmol/gDCW/h yielding 22% (C-mol/C-mol) of MVA from glucose in the aerobic exponential growth phase. The mass balance analysis revealed that the MVA yield of the engineered strain was close to the upper limit at the biomass yield. Since MVA is synthesized from acetyl-CoA using NADPH as a cofactor, the production of MVA affects central metabolism in terms of carbon utilization and NADPH requirements. The reason for this highly efficient MVA production was investigated based on ¹³C-metabolic flux analysis. The estimated flux distributions revealed that the fluxes of acetate formation and the TCA cycle in the engineered strain were lower than those in the control strain. Although the oxidative pentose phosphate pathway is considered as the NADPH generating pathway in E. coli, no difference of the flux was observed between the control and engineered strains. The production/consumption balance of NADPH suggested that additional requirement of NADPH for MVA synthesis was obtained from the transhydrogenase reaction in the engineered strain. Comparison between the measured flux distribution and the ideal values for MVA production proposes a strategy for further engineering to improve the MVA production in E. coli.

The potential of the mevalonate pathway for enhanced isoprenoid production

The cytosol-localised mevalonic acid (MVA) pathway delivers the basic isoprene unit isopentenyl diphosphate (IPP). In higher plants, this central metabolic intermediate is also synthesised by the plastid-localised methylerythritol phosphate (MEP) pathway. Both MVA and MEP pathways conspire through exchange of intermediates and regulatory interactions. Products downstream of IPP such as phytosterols, carotenoids, vitamin E, artemisinin, tanshinone and paclitaxel demonstrate antioxidant, cholesterol-reducing, anti-ageing, anticancer, antimalarial, anti-inflammatory and antibacterial activities. Other isoprenoid precursors including isoprene, isoprenol, geraniol, farnesene and farnesol are economically valuable. An update on the MVA pathway and its interaction with the MEP pathway is presented, including the improvement in the production of phytosterols and other isoprenoid derivatives. Such attempts are for instance based on the bioengineering of microbes such as Escherichia coli and Saccharomyces cerevisiae, as well as plants. The function of relevant genes in the MVA pathway that can be utilised in metabolic engineering is reviewed and future perspectives are presented.

Unprecedented acetoacetyl-coenzyme A synthesizing enzyme of the thiolase superfamily involved in the mevalonate pathway

Acetoacetyl-CoA is the precursor of 3-hydroxy-3-methylglutaryl (HMG)-CoA in the mevalonate pathway, which is essential for terpenoid backbone biosynthesis. Acetoacetyl-CoA is also the precursor of poly-beta-hydroxybutyrate, a polymer belonging to the polyester class produced by microorganisms. The de novo synthesis of acetoacetyl-CoA is usually catalyzed by acetoacetyl-CoA thiolase via a thioester-dependent Claisen condensation reaction between two molecules of acetyl-CoA. Here, we report that nphT7, found in the mevalonate pathway gene cluster from a soil-isolated Streptomyces sp. strain, encodes an unusual acetoacetyl-CoA synthesizing enzyme. The recombinant enzyme overexpressed in Escherichia coli catalyzes a single condensation of acetyl-CoA and malonyl-CoA to give acetoacetyl-CoA and CoA. Replacement of malonyl-CoA with malonyl-(acyl carrier protein) resulted in loss of the condensation activity. No acetoacetyl-CoA synthesizing activity was detected through the condensation of two molecules of acetyl-CoA. Based on these properties of NphT7, we propose to name this unusual enzyme of the thiolase superfamily acetoacetyl-CoA synthase. Coexpression of nphT7 with the HMG-CoA synthase gene and the HMG-CoA reductase gene in a heterologous host allowed 3.5-fold higher production of mevalonate than when only the HMG-CoA synthase and HMG-CoA reductase genes were expressed. This result suggests that nphT7 can be used to significantly increase the concentration of acetoacetyl-CoA in cells, eventually leading to the production of useful terpenoids and poly-beta-hydroxybutyrate.

Bacterial hosts for natural product production

Four bacterial hosts are reviewed in the context of either native or heterologous natural product production. E. coli, B. subtilis, pseudomonads, and Streptomyces bacterial systems are presented with each having either a long-standing or more recent application to the production of therapeutic natural compounds. The four natural product classes focused upon include the polyketides, nonribosomal peptides, terpenoids, and flavonoids. From the perspective of both innate and heterologous production potential, each bacterial host is evaluated according to biological properties that would either hinder or facilitate natural product biosynthesis.

Balancing a heterologous mevalonate pathway for improved isoprenoid production in Escherichia coli

Engineering biosynthetic pathways in microbes for the production of complex chemicals and pharmaceuticals is an attractive alternative to chemical synthesis. However, in transferring large pathways to alternate hosts and manipulating expression levels, the native regulation of carbon flux through the pathway may be lost leading to imbalances in the pathways. Previously, Escherichia coli was engineered to produce large quantities of isoprenoids by creating a mevalonate-based isopentenyl pyrophosphate biosynthetic pathway [Martin, V.J., Pitera, D.J., Withers, S.T., Newman, J.D., Keasling, J.D., 2003. Engineering a mevalonate pathway in Escherichia coli for production of terpenoids. Nat. Biotechnol. 21, 796-802]. The strain produces high levels of isoprenoids, but upon further investigation we discovered that the accumulation of pathway intermediates limited flux and that high-level expression of the mevalonate pathway enzymes inhibited cell growth. Gene titration studies and metabolite profiling using liquid chromatography-mass spectrometry linked the growth inhibition phenotype with the accumulation of the pathway intermediate 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA). Such an accumulation implies that the activity of HMG-CoA reductase was insufficient to balance flux in the engineered pathway. By modulating HMG-CoA reductase production, we eliminated the pathway bottleneck and increased mevalonate production. These results demonstrate that balancing carbon flux through the heterologous pathway is a key determinant in optimizing isoprenoid biosynthesis in microbial hosts.

Enhanced lycopene production inEscherichia coli engineered to synthesize isopentenyl diphosphate and dimethylallyl diphosphate from mevalonate

To increase expression of lycopene synthetic genes crtE, crtB, crtI, and ipiHP1, the four exogenous genes were cloned into a high copy pTrc99A vector with a strong trc promoter. Recombinant Escherichia coli harboring pT-LYCm4 produced 17 mg/L of lycopene. The mevalonate lower pathway, composed of mvaK1, mvaK2, mvaD, and idi, was engineered to produce pSSN12Didi for an efficient supply of the lycopene building blocks, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Mevalonate was supplied as a substrate for the mevalonate lower pathway. Lycopene production in E. coli harboring pT-LYCm4 and pSSN12Didi with supplementation of 3.3 mM mevalonate was more than threefold greater than bacteria with pT-LYCm4 only. Lycopene production was dependent on mevalonate concentration supplied in the culture. Clump formation was observed as cells accumulated more lycopene. Further clumping was prevented by adding the surfactant Tween 80 0.5% (w/v), which also increased lycopene production and cell growth. When recombinant E. coli harboring pT-LYCm4 and pSSN12Didi was cultivated in 2YT medium containing 2% (w/v) glycerol as a carbon source, 6.6 mM mevalonate for the mevalonate lower pathway, and 0.5% (w/v) Tween 80 to prevent clump formation, lycopene production was 102 mg/L and 22 mg/g dry cell weight, and cell growth had an OD(600) value of 15 for 72 h.