Constructing a synthetic constitutive metabolic pathway in Escherichia coli for (R, R)-2,3-butanediol production

Multilevel Systematic Optimization To Achieve Efficient Integrated Expression of Escherichia coli

Genomic integration of heterologous genes is the preferred approach in industrial fermentation-related strains due to the drawbacks associated with plasmid-mediated microbial fermentation, including additional growth burden, genetic instability, and antibiotic contamination. Synthetic biology and genome editing advancements have made gene integration convenient. Integrated expression is extensively used in the field of biomanufacturing and is anticipated to become the prevailing method for expressing recombinant proteins. Therefore, it is pivotal to strengthen the expression of exogenous genes at the genome level. Here, we systematically optimized the integrated expression system of Escherichia coli from 3 aspects. First, the integration site slmA with the highest expression activity was screened out of 18 sites in the ORI region of the E. coli BL21 (DE3) genome. Second, we characterized 16 endogenous promoters in E. coli and combined them with the T7 promoter. A constitutive promoter, Plpp-T7, exhibited significantly higher expression strength than the T7 promoter, achieving a 3.3-fold increase in expression levels. Finally, to further enhance the T7 expression system, we proceeded with overexpression of T7 RNA polymerase at the chassis cell level. The resulting constitutive efficient integrated expression system (CEIES_Ecoli) showed a 2-fold increase in GFP expression compared to the pET3b recombinant plasmid. Therefore, CEIES_Ecoli was applied to the integrated expression of nitrilase and hyaluronidase, achieving stable and efficient enzyme expression, with enzyme activities of 22.87 and 12,195 U·mL-1, respectively, comparable to plasmid levels. Overall, CEIES_Ecoli provides a stable and efficient method of gene expression without the need for antibiotics or inducers, making it a robust tool for synthetic biology, enzyme engineering, and related applications.

Serial adaptive laboratory evolution enhances mixed carbon metabolic capacity of Escherichia coli

Microbes have inherent capacities for utilizing various carbon sources, however they often exhibit sub-par fitness due to low metabolic efficiency. To test whether a bacterial strain can optimally utilize multiple carbon sources, Escherichia coli was serially evolved in L-lactate and glycerol. This yielded two end-point strains that evolved first in L-lactate then in glycerol, and vice versa. The end-point strains displayed a universal growth advantage on single and a mixture of adaptive carbon sources, enabled by a concerted action of carbon source-specialists and generalist mutants. The combination of just four variants of glpK, ppsA, ydcI, and rph-pyrE, accounted for more than 80% of end-point strain fitness. In addition, machine learning analysis revealed a coordinated activity of transcriptional regulators imparting condition-specific regulation of gene expression. The effectiveness of the serial adaptive laboratory evolution (ALE) scheme in bioproduction applications was assessed under single and mixed-carbon culture conditions, in which serial ALE strain exhibited superior productivity of acetoin compared to ancestral strains. Together, systems-level analysis elucidated the molecular basis of serial evolution, which hold potential utility in bioproduction applications.

Enzymes and pathways in microbial production of 2,3-butanediol and 3-acetoin isomers

2,3-Butanediol (BD) and acetoin (AC) are products of the non-oxidative metabolism of microorganisms, presenting industrial importance due to their wide range of applications and high market value. Their optical isomers have particular applications, justifying the efforts on the selective bioproduction. Each microorganism produces different isomer mixtures, as a consequence of having different butanediol dehydrogenase (BDH) enzymes. However, the whole scene of the isomer bioproduction, considering the several enzymes and conditions, has not been completely elucidated. Here we show the BDH classification as R, S or meso by bioinformatics analysis uncovering the details of the isomers production. The BDH was compared to diacetyl reductases (DAR) and the new enoyl reductases (ER). We observed that R-BDH is the most singular BDH, while meso and S-BDHs are similar and may be better distinguished through their stereo-selective triad. DAR and ER showed distinct stereo-triads from those described for BDHs, agreeing with kinetic data from the literature and our phylogenetic analysis. The ER family probably has meso-BDH like activity as already demonstrated for a single sequence from this group. These results are of great relevance, as they organize BD producing enzymes, to our known, never shown before in the literature. This review also brings attention to nontraditional enzymes/pathways that can be involved with BD/AC synthesis, as well as oxygen conditions that may lead to the differential production of their isomers. Together, this information can provide helpful orientation for future studies in the field of BD/AC biological production, thus contributing to achieve their production on an industrial scale.

Metabolic Engineering and Regulation of Diol Biosynthesis from Renewable Biomass in Escherichia coli

As bulk chemicals, diols have wide applications in many fields, such as clothing, biofuels, food, surfactant and cosmetics. The traditional chemical synthesis of diols consumes numerous non-renewable energy resources and leads to environmental pollution. Green biosynthesis has emerged as an alternative method to produce diols. Escherichia coli as an ideal microbial factory has been engineered to biosynthesize diols from carbon sources. Here, we comprehensively summarized the biosynthetic pathways of diols from renewable biomass in E. coli and discussed the metabolic-engineering strategies that could enhance the production of diols, including the optimization of biosynthetic pathways, improvement of cofactor supplementation, and reprogramming of the metabolic network. We then investigated the dynamic regulation by multiple control modules to balance the growth and production, so as to direct carbon sources for diol production. Finally, we proposed the challenges in the diol-biosynthesis process and suggested some potential methods to improve the diol-producing ability of the host.

Acetic acid acting as a signaling molecule in the quorum sensing system increases 2,3-butanediol production in Saccharomyces cerevisiae

2,3-Butanediol (2,3-BD) has been extensively used in chemical syntheses. This study aimed to explore acetic acid as a signaling molecule that activates a quorum sensing (QS) system to promote the production of 2,3-BD. The yield of 2,3-BD is proportional to the cell density. Saccharomyces cerevisiae W141 does not produce 2,3-BD when the cell density is lower than the threshold concentration (OD_600 nm = 10 or cell density 4.4 × 10⁸ CFU/mL). When 1.5 g/L acetic acid is added, the yield of 2,3-BD is 3.01 ± 0.04 g/L. Subsequently, S. cerevisiae W141 was cocultured with Acetobacter pasteurianus Huniang 1.01 under the optimal conditions, the acetic acid production was increased by 76.7% and 30.6% compared with the original strain and the strain cultivated with 1.5 g/L acetic acid, and the yield of 2,3-BD was increased by 81.9% and 3.3%, respectively. This difference is due to the activity of acetyl lactic acid synthase (ILV2) and 2,3-BD dehydrogenase (BDH1), as the relative expression of the ilv2 and bdh1 genes is increased. The results showed that the biosynthesis of 2,3-BD was regulated by acetic acid as a signaling molecule. S. cerevisiae is a promising host for producing 2,3-BD for industrial applications.

Prospects on bio-based 2,3-butanediol and acetoin production: Recent progress and advances

The bio-based platform chemicals 2,3-butanediol (BDO) and acetoin have various applications in chemical, cosmetics, food, agriculture, and pharmaceutical industries, whereas the derivatives of BDO could be used as fuel additives, polymer and synthetic rubber production. This review summarizes the novel technological developments in adapting genetic and metabolic engineering strategies for selection and construction of chassis strains for BDO and acetoin production. The valorization of renewable feedstocks and bioprocess development for the upstream and downstream stages of bio-based BDO and acetoin production are discussed. The techno-economic aspects evaluating the viability and industrial potential of bio-based BDO production are presented. The commercialization of bio-based BDO and acetoin production requires the utilization of crude renewable resources, the chassis strains with high fermentation production efficiencies and development of sustainable purification or conversion technologies.

A Golden-Gate Based Cloning Toolkit to Build Violacein Pathway Libraries in Yarrowia lipolytica

Violacein is a naturally occurring anticancer therapeutic compound with deep purple color. In this work, we harnessed the modular and combinatorial feature of a Golden Gate assembly method to construct a library of violacein producing strains in the oleaginous yeast Yarrowia lipolytica, where each gene in the violacein pathway was controlled by three different promoters with varying transcriptional strength. After optimizing the linker sequence and the Golden Gate reaction, we achieved high transformation efficiency and obtained a panel of representative Y. lipolytica recombinant strains. By evaluating the gene expression profile of 21 yeast strains, we obtained three colorful compounds in the violacein pathway: green (proviolacein), purple (violacein), and pink (deoxyviolacein). Our results indicated that strong expression of VioB, VioC, and VioD favors violacein production with minimal byproduct deoxyvioalcein in Y. lipolytica, and high deoxyviolacein production was found strongly associated with the weak expression of VioD. By further optimizing the carbon to nitrogen ratio and cultivation pH, the maximum violacein reached 70.04 mg/L with 5.28 mg/L of deoxyviolacein in shake flasks. Taken together, the development of Golden Gate cloning protocols to build combinatorial pathway libraries, and the optimization of culture conditions set a new stage for accessing the violacein pathway intermediates and engineering violacein production in Y. lipolytica. This work further expands the toolbox to engineering Y. lipolytica as an industrially relevant host for plant or marine natural product biosynthesis.

Metabolic engineering of Escherichia coli for 2,3-butanediol production from cellulosic biomass by using glucose-inducible gene expression system

A glucose-inducible gene expression system has been developed using HexR-P_zwf1 of Pseudomonas putida to induce the metabolic pathways. Since the system is controlled by an Entner-Doudoroff pathway (EDP) intermediate, the EDP of Escherichia coli was activated by deleting pfkA and gntR genes. Growth experiment with green fluorescent protein as a reporter indicated that the induction of this system was tightly controlled over a wide range of glucose in E. coli without adding any inducer. 2,3-butanediol (BDO) synthetic pathway genes were expressed by this system in the pfkA-gntR-deleted strain. The resultant engineered strain harbouring this system efficiently produced BDO with a 71% increased titer than the control strain. The strain was also able to produce BDO from a mixture of glucose and xylose which is comparable to glucose alone. Further, the strain produced 11 g/L of BDO at a yield of 0.48 g/g from the hydrolysate of empty palm fruit bunches. This system can also be applied in many other bio-production processes from lignocellulosic biomass.

Engineered E. coli W enables efficient 2,3-butanediol production from glucose and sugar beet molasses using defined minimal medium as economic basis

Background

Efficient microbial production of chemicals is often hindered by the cytotoxicity of the products or by the pathogenicity of the host strains. Hence 2,3-butanediol, an important drop-in chemical, is an interesting alternative target molecule for microbial synthesis since it is non-cytotoxic. Metabolic engineering of non-pathogenic and industrially relevant microorganisms, such as Escherichia coli, have already yielded in promising 2,3-butanediol titers showing the potential of microbial synthesis of 2,3-butanediol. However, current microbial 2,3-butanediol production processes often rely on yeast extract as expensive additive, rendering these processes infeasible for industrial production.

Results

The aim of this study was to develop an efficient 2,3-butanediol production process with E. coli operating on the premise of using cost-effective medium without complex supplements, considering second generation feedstocks. Different gene donors and promoter fine-tuning allowed for construction of a potent E. coli strain for the production of 2,3-butanediol as important drop-in chemical. Pulsed fed-batch cultivations of E. coli W using microaerobic conditions showed high diol productivity of 4.5 g l⁻¹ h⁻¹. Optimizing oxygen supply and elimination of acetoin and by-product formation improved the 2,3-butanediol titer to 68 g l⁻¹, 76% of the theoretical maximum yield, however, at the expense of productivity. Sugar beet molasses was tested as a potential substrate for industrial production of chemicals. Pulsed fed-batch cultivations produced 56 g l⁻¹ 2,3-butanediol, underlining the great potential of E. coli W as production organism for high value-added chemicals.

Conclusion

A potent 2,3-butanediol producing E. coli strain was generated by considering promoter fine-tuning to balance cell fitness and production capacity. For the first time, 2,3-butanediol production was achieved with promising titer, rate and yield and no acetoin formation from glucose in pulsed fed-batch cultivations using chemically defined medium without complex hydrolysates. Furthermore, versatility of E. coli W as production host was demonstrated by efficiently converting sucrose from sugar beet molasses into 2,3-butanediol.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1038-0) contains supplementary material, which is available to authorized users.

Production of optically pure 2,3-butanediol from Miscanthus floridulus hydrolysate using engineered Bacillus licheniformis strains

2,3-Butanediol (2,3-BD) can be produced by fermentation of natural resources like Miscanthus. Bacillus licheniformis mutants, WX-02ΔbudC and WX-02ΔgldA, were elucidated for the potential to use Miscanthus as a cost-effective biomass to produce optically pure 2,3-BD. Both WX-02ΔbudC and WX-02ΔgldA could efficiently use xylose as well as mixed sugars of glucose and xylose to produce optically pure 2,3-BD. Batch fermentation of M. floridulus hydrolysate could produce 21.6 g/L D-2,3-BD and 23.9 g/L meso-2,3-BD in flask, and 13.8 g/L D-2,3-BD and 13.2 g/L meso-2,3-BD in bioreactor for WX-02ΔbudC and WX-02ΔgldA, respectively. Further fed-batch fermentation of hydrolysate in bioreactor showed both of two strains could produce optically pure 2,3-BD, with 32.2 g/L D-2,3-BD for WX-02ΔbudC and 48.5 g/L meso-2,3-BD for WX-02ΔgldA, respectively. Collectively, WX-02ΔbudC and WX-02ΔgldA can efficiently produce optically pure 2,3-BD with M. floridulus hydrolysate, and these two strains are candidates for industrial production of optical purity of 2,3-BD with M. floridulus hydrolysate.

Recent advances on production of 2, 3-butanediol using engineered microbes

As a significant platform chemical, 2, 3-butanediol (2, 3-BD) has found wide applications in industry. The success of microbial 2, 3-BD production was limited by the use of pathogenic microorganisms and low titer in engineered hosts. The utilization of cheaply available feedstock such as lignocellulose was another major challenge to achieve economic production of 2, 3-BD. To address those issues, engineering strategies including both genetic modifications and process optimization have been employed. In this review, we summarized the state-of-the-art progress in the biotechnological production of 2, 3-BD. Metabolic engineering and process engineering strategies were discussed.

Production of (2R, 3R)-2,3-butanediol using engineered Pichia pastoris: strain construction, characterization and fermentation

BACKGROUND

2,3-butanediol (2,3-BD) is a bulk platform chemical with various potential applications such as aviation fuel. 2,3-BD has three optical isomers: (2R, 3R)-, (2S, 3S)- and meso-2,3-BD. Optically pure 2,3-BD is a crucial precursor for the chiral synthesis and it can also be used as anti-freeze agent due to its low freezing point. 2,3-BD has been produced in both native and non-native hosts. Several pathogenic bacteria were reported to produce 2,3-BD in mixture of its optical isomers including Klebsiella pneumoniae and Klebsiella oxytoca. Engineered hosts based on episomal plasmid expression such as Escherichia coli, Saccharomyces cerevisiae and Bacillus subtilis are not ideal for industrial fermentation due to plasmid instability.

RESULTS

Pichia pastoris is generally regarded as safe and a well-established host for high-level heterologous protein production. To produce pure (2R, 3R)-2,3-BD enantiomer, we developed a P. pastoris strain by introducing a synthetic pathway. The alsS and alsD genes from B. subtilis were codon-optimized and synthesized. The BDH1 gene from S. cerevisiae was cloned. These three pathway genes were integrated into the genome of P. pastoris and expressed under the control of GAP promoter. Production of (2R, 3R)-2,3-BD was achieved using glucose as feedstock. The optical purity of (2R, 3R)-2,3-BD was more than 99%. The titer of (2R, 3R)-2,3-BD reached 12 g/L with 40 g/L glucose as carbon source in shake flask fermentation. The fermentation conditions including pH, agitation speeds and aeration rates were optimized in batch cultivations. The highest titer of (2R, 3R)-2,3-BD achieved in fed-batch fermentation using YPD media was 45 g/L. The titer of 2,3-BD was enhanced to 74.5 g/L through statistical medium optimization.

CONCLUSIONS

The potential of engineering P. pastoris into a microbial cell factory for biofuel production was evaluated in this work using (2R, 3R)-2,3-BD as an example. Engineered P. pastoris could be a promising workhorse for the production of optically pure (2R, 3R)-2,3-BD.

A shortened, two-enzyme pathway for 2,3-butanediol production in Escherichia coli

The platform chemical 2,3-butanediol (2,3-BDO) is produced by a number of microorganisms via a three-enzyme pathway starting from pyruvate. Here, we report production of 2,3-BDO via a shortened, two-enzyme pathway in Escherichia coli. A synthetic operon consisting of the acetolactate synthase (ALS) and acetoin reductase (AR) genes from Enterobacter under control of the T7 promoter was cloned in an episomal plasmid. E. coli transformed with this plasmid produced 2,3-BDO and the pathway intermediate acetoin, demonstrating that the shortened pathway was functional. To assemble a synthetic operon for inducer- and plasmid-free production of 2,3-BDO, ALS and AR genes were integrated in the E. coli genome under control of the constitutive ackA promoter. Shake flask-level cultivation led to accumulation of ~1 g/L acetoin and ~0.66 g/L 2,3-BDO in the medium. The novel biosynthetic route for 2,3-BDO biosynthesis described herein provides a simple and cost-effective approach for production of this important chemical.

Chromosome engineering of Escherichia coli for constitutive production of salvianic acid A

Background

Salvianic acid A (SAA), a valuable natural product from herbal plant Salvia miltiorrhiza, exhibits excellent antioxidant activities on food industries and efficacious therapeutic potential on cardiovascular diseases. Recently, production of SAA in engineered Escherichia coli was established via the artificial biosynthetic pathway of SAA on the multiple plasmids in our previous work. However, the plasmid-mediated system required to supplement expensive inducers and antibiotics during the fermentation process, restricting scale-up production of SAA. Microbial cell factory would be an attractive approach for constitutive production of SAA by chromosome engineering.

Results

The limited enzymatic reactions in SAA biosynthetic pathway from glucose were grouped into three modules, which were sequentially integrated into chromosome of engineered E. coli by λ Red homologous recombination method. With starting strain E. coli BAK5, in which the ptsG, pykF, pykA, pheA and tyrR genes were previously deleted, chassis strain BAK11 was constructed for constitutive production of precursor l-tyrosine by replacing the 17.7-kb mao-paa cluster with module 1 (P_lacUV5-aroG^fbr-tyrA^fbr-aroE) and the lacI gene with module 2 (P_trc-glk-tktA-ppsA). The synthetic 5tacs promoter demonstrated the optimal strength to drive the expression of hpaBC-d-ldh^Y52A in module 3, which then was inserted at the position between nupG and speC on the chromosome of strain BAK11. The final strain BKD13 produced 5.6 g/L of SAA by fed-batch fermentation in 60 h from glucose without any antibiotics and inducers supplemented.

Conclusions

The plasmid-free and inducer-free strain for SAA production was developed by targeted integration of the constitutive expression of SAA biosynthetic genes into E. coli chromosome. Our work provides the industrial potential for constitutive production of SAA by the indel microbial cell factory and also sets an example of further producing other valuable natural and unnatural products.

Electronic supplementary material

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Metabolic engineering of indole pyruvic acid biosynthesis in Escherichia coli with tdiD

Background

Indole pyruvic acid (IPA) is a versatile platform intermediate and building block for a number of high-value products in the pharmaceutical and food industries. It also has a wide range of applications, such as drugs for the nervous system, cosmetics, and luminophores. Chemical synthesis of IPA is a complicated and costly process. Moreover, through the biosynthesis route employing l-amino acid oxidase, the byproduct hydrogen peroxide leads the degradation of IPA. TdiD, identified as a specific tryptophan aminotransferase, could be an alternative solution for efficient IPA biosynthesis.

Results

Escherichia coli strain W3110, which demonstrates basic production when supplied with tryptophan, was engineered for IPA biosynthesis. Several strategies were implemented to improve IPA production. First, through incorporating the codon-optimized tdiD into W3110, IPA levels increased from 41.54 ± 1.26 to 52.54 ± 2.08 mg/L. Second, after verifying the benefit of an increased phenylpyruvate pool, a YL03 strain was constructed based on a previously reported mutant strain of W3110 with a plasmid carrying aroF^fbr and pheA^fbr to further improve IPA production. The recombinant YL03 strain accumulated IPA at 158.85 ± 5.36 mg/L, which was 3.82-fold higher than that of the wild-type W3110 strain. Third, optimization of tdiD^co expression was carried out by replacing the Trc promoter with a series of constitutively active promoters along with increasing the plasmid copy numbers. The highest IPA production was observed in YL08, which achieved 236.42 ± 17.66 mg/L and represented a greater than 5-fold increase as compared to W3110. Finally, the effects of deletion and overexpression of tnaA on IPA biosynthesis were evaluated. The removal of tnaA led to slightly reduced IPA levels, whereas the overexpression of tnaA resulted in a considerable decline in production.

Conclusions

This study illustrates the feasibility of IPA biosynthesis in E. coli through tdiD. An efficient IPA producing strain, YL08, was developed, which provides a new possibility for biosynthesis of IPA. Although the final production was limited, this study demonstrates a convenient method of IPA synthesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0620-6) contains supplementary material, which is available to authorized users.

Sortase A-Mediated Metabolic Enzyme Ligation in Escherichia coli

We demonstrate metabolic enzyme ligation using a transpeptidase (Staphylococcal sortase A) in the microbial cytoplasm for the redirection of metabolic flux through metabolic channeling. Here, sortase A expression was controlled by the lac promoter to trigger metabolic channeling by the addition of isopropyl-β-d-thiogalactopyranoside (IPTG). We tested covalent linking of pyruvate-formate lyase and phosphate acetyltransferase by sortase A-mediated ligation and evaluated the production of acetate. The time point of addition of IPTG was not critical for facilitating metabolic enzyme ligation, and acetate production increased upon expression of sortase A. These results show that sortase A-mediated enzyme ligation enhances an acetate-producing flux in E. coli. We have validated that sortase A-mediated enzyme ligation offers a metabolic channeling approach to redirect a central flux to a desired flux.

High Production of 2,3-Butanediol (2,3-BD) by Raoultella ornithinolytica B6 via Optimizing Fermentation Conditions and Overexpressing 2,3-BD Synthesis Genes

Biological production of 2,3-butandiol (2,3-BD) has received great attention as an alternative to the petroleum-based 2,3-BD production. In this study, a high production of 2,3-BD in fed-batch fermentation was investigated with a newly isolated bacterium designated as Raoultella ornithinolytica B6. The isolate produced 2,3-BD as the main product using hexoses (glucose, galactose, and fructose), pentose (xylose) and disaccharide (sucrose). The effects of temperature, pH-control schemes, and agitation speeds on 2,3-BD production were explored to optimize the fermentation conditions. Notably, cell growth and 2,3-BD production by R. ornithinolytica B6 were higher at 25°C than at 30°C. When three pH control schemes (no pH control, pH control at 7, and pH control at 5.5 after the pH was decreased to 5.5 during fermentation) were tested, the best 2,3-BD titer and productivity along with reduced by-product formation were achieved with pH control at 5.5. Among different agitation speeds (300, 400, and 500 rpm), the optimum agitation speed was 400 rpm with 2,3-BD titer of 68.27 g/L, but acetic acid was accumulated up to 23.32 g/L. Further enhancement of the 2,3-BD titer (112.19 g/L), yield (0.38 g/g), and productivity (1.35 g/L/h) as well as a significant reduction of acetic acid accumulation (9.71 g/L) was achieved by the overexpression of homologous budABC genes, the 2,3-BD-synthesis genes involved in the conversion of pyruvate to 2,3-BD. This is the first report presenting a high 2,3-BD production by R.ornithinolytica which has attracted little attention with respect to 2,3-BD production, extending the microbial spectrum of 2,3-BD producers.

Metabolic engineering of Zymomonas mobilis for 2,3-butanediol production from lignocellulosic biomass sugars

BACKGROUND

To develop pathways for advanced biofuel production, and to understand the impact of host metabolism and environmental conditions on heterologous pathway engineering for economic advanced biofuels production from biomass, we seek to redirect the carbon flow of the model ethanologen Zymomonas mobilis to produce desirable hydrocarbon intermediate 2,3-butanediol (2,3-BDO). 2,3-BDO is a bulk chemical building block, and can be upgraded in high yields to gasoline, diesel, and jet fuel.

RESULTS

2,3-BDO biosynthesis pathways from various bacterial species were examined, which include three genes encoding acetolactate synthase, acetolactate decarboxylase, and butanediol dehydrogenase. Bioinformatics analysis was carried out to pinpoint potential bottlenecks for high 2,3-BDO production. Different combinations of 2,3-BDO biosynthesis metabolic pathways using genes from different bacterial species have been constructed. Our results demonstrated that carbon flux can be deviated from ethanol production into 2,3-BDO biosynthesis, and all three heterologous genes are essential to efficiently redirect pyruvate from ethanol production for high 2,3-BDO production in Z. mobilis. The down-selection of best gene combinations up to now enabled Z. mobilis to reach the 2,3-BDO production of more than 10 g/L from glucose and xylose, as well as mixed C6/C5 sugar streams derived from the deacetylation and mechanical refining process.

CONCLUSIONS

This study confirms the value of integrating bioinformatics analysis and systems biology data during metabolic engineering endeavors, provides guidance for value-added chemical production in Z. mobilis, and reveals the interactions between host metabolism, oxygen levels, and a heterologous 2,3-BDO biosynthesis pathway. Taken together, this work provides guidance for future metabolic engineering efforts aimed at boosting 2,3-BDO titer anaerobically.