High rate 2,3-butanediol production with Vibrio natriegens

Efficient natural plasmid transformation of Vibrio natriegens enables zero-capital molecular biology

The fast-growing microbe Vibrio natriegens is capable of natural transformation where it draws DNA in from media via an active process under physiological conditions. Using an engineered strain with a genomic copy of the master competence regulator tfoX from Vibrio cholerae in combination with a new minimal competence media (MCM) that uses acetate as an energy source, we demonstrate naturally competent cells which are created, transformed, and recovered entirely in the same media, without exchange or addition of fresh media. Cells are naturally competent to plasmids, recombination with linear DNA, and cotransformation of both to select for scarless and markerless genomic edits. The entire process is simple and inexpensive, requiring no capital equipment for an entirely room temperature process (zero capital protocol, 104 cfu/μg), or just an incubator (high-efficiency protocol, 105-6 cfu/μg). These cells retain their naturally competent state when frozen and are transformable immediately upon thawing like a typical chemical or electrochemical competent cell. Since the optimized transformation protocol requires only 50 min of hands-on time, and V. natriegens grows quickly even on plates, a transformation started at 9 AM yields abundant culturable single colonies by 5 PM. Further, because all stages of transformation occur in the same media, and the process can be arbitrarily scaled in volume, this natural competence strain and media could be ideal for automated directed evolution applications. As a result, naturally competent V. natriegens could compete with Escherichia coli as an excellent chassis for low-cost and highly scalable synthetic biology.

Investigation of exopolysaccharide formation and its impact on anaerobic succinate production with Vibrio natriegens

Vibrio natriegens is an emerging host for biotechnology due to its high growth and substrate consumption rates. In industrial processes typically fed-batch processes are applied to obtain high space-time yields. In this study, we established an aerobic glucose-limited fed-batch fermentation with the wild type (wt) of V. natriegens which yielded biomass concentrations of up to 28.4 gX  L-1 . However, we observed that the viscosity of the culture broth increased by a factor of 800 at the end of the cultivation due to the formation of 157 ± 20 mg exopolysaccharides (EPS) L-1 . Analysis of the genomic repertoire revealed several genes and gene clusters associated with EPS formation. Deletion of the transcriptional regulator cpsR in V. natriegens wt did not reduce EPS formation, however, it resulted in a constantly low viscosity of the culture broth and altered the carbohydrate content of the EPS. A mutant lacking the cps cluster secreted two-fold less EPS compared to the wt accompanied by an overall low viscosity and a changed EPS composition. When we cultivated the succinate producer V. natriegens Δlldh Δdldh Δpfl Δald Δdns::pycCg (Succ1) under anaerobic conditions on glucose, we also observed an increased viscosity at the end of the cultivation. Deletion of cpsR and the cps cluster in V. natriegens Succ1 reduced the viscosity five- to six-fold which remained at the same level observed at the start of the cultivation. V. natriegens Succ1 ΔcpsR and V. natriegens Succ1 Δcps achieved final succinate concentrations of 51 and 46 g L-1 with a volumetric productivity of 8.5 and 7.7 gSuc L-1  h-1 , respectively. Both strains showed a product yield of about 1.4 molSuc molGlc -1 , which is 27% higher compared with that of V. natriegens Succ1 and corresponds to 81% of the theoretical maximum.

Metabolic engineering of fast-growing Vibrio natriegens for efficient pyruvate production

BACKGROUND

Pyruvate is a widely used value-added chemical which also serves as a hub of various metabolic pathways. The fastest-growing bacterium Vibrio natriegens is a promising chassis for synthetic biology applications with high substrate uptake rates. The aim of this study was to investigate if the high substrate uptake rates of V. natriegens enable pyruvate production at high productivities.

RESULTS

Two prophage gene clusters and several essential genes for the biosynthesis of byproducts were first deleted. In order to promote pyruvate accumulation, the key gene aceE encoding pyruvate dehydrogenase complex E1 component was down-regulated to reduce the carbon flux into the tricarboxylic acid cycle. Afterwards, the expression of ppc gene encoding phosphoenolpyruvate carboxylase was fine-tuned to balance the cell growth and pyruvate synthesis. The resulting strain PYR32 was able to produce 54.22 g/L pyruvate from glucose within 16 h, with a yield of 1.17 mol/mol and an average productivity of 3.39 g/L/h. In addition, this strain was also able to efficiently convert sucrose or gluconate into pyruvate at high titers.

CONCLUSION

A novel strain of V. natriegens was engineered which was capable to provide higher productivity in pyruvate synthesis. This study lays the foundation for the biosynthesis of pyruvate and its derivatives in fast-growing V. natriegens.

Anodic Respiration of Vibrio natriegens in a Bioelectrochemical System

Vibrio natriegens promises to be a new standard biotechnological working organism since it grows extraordinarily fast, its productivity surpasses E. coli by far, and genomic tools are getting readily available. Recent studies provided insights into its extracellular electron transfer pathway, revealing it to be similar to other well-known electroactive organisms. Therefore, we aimed to show for the first time that V. natriegens donates electrons from its metabolism to an electrode by direct contact as well as via an artificial redox mediator. Our results demonstrate current densities up to 196 μA cm-2 using an artificial mediator. Via direct electron transfer, 6.6 μA cm-2 were achieved within the first 24 h of cultivation. In the mediated system, mainly formate, acetate, and succinate were produced from glucose. These findings favor V. natriegens over established electroactive organisms due to its superior electron-transfer capabilities combined with an outstanding metabolism.

Systems biology of competency in Vibrio natriegens is revealed by applying novel data analytics to the transcriptome

Vibrio natriegens regulates natural competence through the TfoX and QstR transcription factors, which are involved in external DNA capture and transport. However, the extensive genetic and transcriptional regulatory basis for competency remains unknown. We used a machine-learning approach to decompose Vibrio natriegens's transcriptome into 45 groups of independently modulated sets of genes (iModulons). Our findings show that competency is associated with the repression of two housekeeping iModulons (iron metabolism and translation) and the activation of six iModulons; including TfoX and QstR, a novel iModulon of unknown function, and three housekeeping iModulons (representing motility, polycations, and reactive oxygen species [ROS] responses). Phenotypic screening of 83 gene deletion strains demonstrates that loss of iModulon function reduces or eliminates competency. This database-iModulon-discovery cycle unveils the transcriptomic basis for competency and its relationship to housekeeping functions. These results provide the genetic basis for systems biology of competency in this organism.

Identification of Emerging Industrial Biotechnology Chassis Vibrio natriegens as a Novel High Salt-Tolerant and Feedstock Flexibility Electroactive Microorganism for Microbial Fuel Cell

The development of MFC using electroactive industrial microorganisms has seen a surge of interest because of the co-generation for bioproduct and electricity production. Vibrio natriegens as a promising next-generation industrial microorganism chassis and its application for microbial fuel cells (MFC) was first studied. Mediated electron transfer was found in V. natriegens MFC (VMFC), but V. natriegens cannot secrete sufficient electron mediators to transfer electrons to the anode. All seven electron mediators supplemented are capable of improving the electronic transfer efficiency of VMFC. The media and carbon sources switching study reveals that VMFCs have excellent bioelectricity generation performance with feedstock flexibility and high salt-tolerance. Among them, 1% glycerol as the sole carbon source produced the highest power density of 111.9 ± 6.7 mW/cm². The insight of the endogenous electronic mediators found that phenazine-1-carboxamide, phenazine-1-carboxylic acid, and 1-hydroxyphenazine are synthesized by V. natriegens via the shikimate pathway and the phenazine synthesis and modification pathways. This work provides the first proof for emerging industrial biotechnology chassis V. natriegens as a novel high salt-tolerant and feedstock flexibility electroactive microorganism for MFC, and giving insight into the endogenous electron mediator biosynthesis of VMFC, paving the way for the application of V. natriegens in MFC and even microbial electrofermentation (EF).

Genome-Scale Modeling and Systems Metabolic Engineering of Vibrio natriegens for the Production of 1,3-Propanediol

The fastest-growing bacterium Vibrio natriegens is a highly promising next-generation workhorse for molecular biology and industrial biotechnology. In this work, we described the workflows for developing genome-scale metabolic models and genome-editing protocols for engineering Vibrio natriegens. A case study for metabolic engineering of Vibrio natriegens for the production of 1,3-propanediol was also presented.

Non-Sterilized Fermentation of 2,3-Butanediol with Seawater by Metabolic Engineered Fast-Growing Vibrio natriegens

Sustainable and environment-friendly microbial fermentation processes have been developed to produce numerous chemicals. However, the high energy input required for sterilization and substantial fresh water consumption restrict the economic feasibility of traditional fermentation processes. To address these problems, Vibrio natriegens, a promising microbial chassis with low nutritional requirements, high salt tolerance and rapid growth rate can be selected as the host for chemical production. In this study, V. natriegens was metabolic engineered to produce 2,3-butanediol (2,3-BD), an important platform chemical, through non-sterilized fermentation with seawater-based minimal medium after expressing a 2,3-BD synthesis cluster and deleting two byproduct encoding genes. Under optimized fermentative conditions, 41.27 g/L 2,3-BD was produced with a productivity of 3.44 g/L/h and a yield of 0.39 g/g glucose by recombinant strain V. natriegensΔfrdAΔldhA-pETRABC. This study confirmed the feasibility of non-sterilized fermentation using seawater to replace freshwater and other valuable chemicals may also be produced through metabolic engineering of the emerging synthetic biology chassis V. natriegens.

Overexpression of recombinant proteins containing non-canonical amino acids in Vibrio natriegens: p-azido-L-phenylalanine as coupling site for 19F-tags

Vibrio natriegens is the fastest growing organism identified so far. The minimum doubling time of only 9.4 min, the ability to utilize over 60 different carbon sources and its non-pathogenic properties make it an interesting alternative to E. coli as a new production host for recombinant proteins. We investigated the ability of the engineered V. natriegens strain, Vmax™ Express, to incorporate the non-canonical amino acid (ncAA) p-azido-L-phenylalanine (AzF) into recombinant proteins for NMR applications. AzF was incorporated into enhanced yellow fluorescent protein (EYFP) and MlaC, an intermembrane transport protein, by stop codon suppression. AzF incorporation into EYFP resulted in an improved suppression efficiency (SE) of up to 35.5 ± 0.8% and a protein titer of 26.7 ± 0.7 mg/L. The expression levels of MlaC-AzF even exceeded those of E. coli BL21 cells. For the recording of 1H-15N and 19F NMR spectra, EYFP-AzF was expressed and isotopically labeled in minimal medium and the newly introduced azido-group was used as coupling site for NMR sensitive 19F-tags. Our findings show that Vmax is a flexible expression host, suitable for the incorporation of ncAAs in recombinant proteins with the potential to surpass protein yields of E. coli. The presented method suggests the implementation of V. natriegens for expression of isotopically labeled proteins containing ncAAs, which can be chemically modified for the application in protein-observed 19F-NMR.

A Vibrio-based microbial platform for accelerated lignocellulosic sugar conversion

Background

Owing to increasing concerns about climate change and the depletion of fossil fuels, the development of efficient microbial processes for biochemical production from lignocellulosic biomass has been a key issue. Because process efficiency is greatly affected by the inherent metabolic activities of host microorganisms, it is essential to utilize a microorganism that can rapidly convert biomass-derived sugars. Here, we report a novel Vibrio-based microbial platform that can rapidly and simultaneously consume three major lignocellulosic sugars (i.e., glucose, xylose, and arabinose) faster than any previously reported microorganisms.

Results

The xylose isomerase pathway was constructed in Vibrio sp. dhg, which naturally displays high metabolic activities on glucose and arabinose but lacks xylose catabolism. Subsequent adaptive laboratory evolution significantly improved xylose catabolism of initial strain and led to unprecedently high growth and sugar uptake rate (0.67 h⁻¹ and 2.15 g g_{dry cell weight}⁻¹ h⁻¹, respectively). Furthermore, we achieved co-consumption of the three sugars by deletion of PtsG and introduction of GalP. We validated its superior performance and applicability by demonstrating efficient lactate production with high productivity (1.15 g/L/h) and titer (83 g/L).

Conclusions

In this study, we developed a Vibrio-based microbial platform with rapid and simultaneous utilization of the three major sugars from lignocellulosic biomass by applying an integrated approach of rational and evolutionary engineering. We believe that the developed strain can be broadly utilized to accelerate the production of diverse biochemicals from lignocellulosic biomass.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02157-3.

Conversion of Food Waste into 2,3-Butanediol via Thermophilic Fermentation: Effects of Carbohydrate Content and Nutrient Supplementation

Fermentation of food waste into 2,3-butanediol (2,3-BDO), a high-value chemical, is environmentally sustainable and an inexpensive method to recycle waste. Compared to traditional mesophilic fermentation, thermophilic fermentation can inhibit the growth of contaminant bacteria, thereby improving the success of food waste fermentation. However, the effects of sugar and nutrient concentrations in thermophilic food waste fermentations are currently unclear. Here, we investigated the effects of sugar and nutrients (yeast extract (YE) and peptone) concentrations on 2,3-BDO production from fermenting glucose and food waste media using the newly isolated thermophilic Bacillus licheniformis YNP5-TSU. When glucose media was used, fermentation was greatly affected by sugar and nutrient concentrations: excessive glucose (>70 g/L) slowed down the fermentation and low nutrients (2 g/L YE and 1 g/L peptone) caused fermentation failure. However, when food waste media were used with low nutrient addition, the bacteria consumed all 57.8 g/L sugars within 24 h and produced 24.2 g/L 2,3-BDO, equivalent to a fermentation yield of 0.42 g/g. An increase in initial sugar content (72.9 g/L) led to a higher 2,3-BDO titer of 36.7 g/L with a nearly theoretical yield of 0.47 g/g. These findings may provide fundamental knowledge for designing cost-effective food waste fermentation to produce 2,3-BDO.

Metabolic engineering of Vibrio natriegens for anaerobic succinate production

The biotechnological production of succinate bears serious potential to fully replace existing petrochemical approaches in the future. In order to establish an economically viable bioprocess, obtaining high titre, yield and productivity is of central importance. In this study, we present a straightforward engineering approach for anaerobic succinate production with Vibrio natriegens, consisting of essential metabolic engineering and optimization of process conditions. The final producer strain V. natriegens Δlldh Δdldh Δpfl Δald Δdns::pyc_Cg (Succ1) yielded 1.46 mol of succinate per mol of glucose under anaerobic conditions (85% of the theoretical maximum) and revealed a particularly high biomass‐specific succinate production rate of 1.33 g_Succ g_CDW⁻¹ h⁻¹ compared with well‐established production systems. By applying carbon and redox balancing, we determined the intracellular flux distribution and show that under the tested conditions the reductive TCA as well as the oxidative TCA/glyoxylate pathway contributed to succinate formation. In a zero‐growth bioprocess using minimal medium devoid of complex additives and expensive supplements, we obtained a final titre of 60.4 g_Succ l⁻¹ with a maximum productivity of 20.8 g_Succ l⁻¹ h⁻¹ and an overall volumetric productivity of 8.6 g_Succ l⁻¹ h⁻¹ during the 7 h fermentation. The key performance indicators (titre, yield and productivity) of this first engineering approach in V. natriegens are encouraging and compete with costly tailored microbial production systems.

Biosensor-based isolation of amino acid-producing Vibrio natriegens strains

The marine bacterium Vibrio natriegens has recently been demonstrated to be a promising new host for molecular biology and next generation bioprocesses. V. natriegens is a Gram-negative, non-pathogenic slight-halophilic bacterium, with a high nutrient versatility and a reported doubling time of under 10 min. However, V. natriegens is not an established model organism yet, and further research is required to promote its transformation into a microbial workhorse.

In this work, the potential of V. natriegens as an amino acid producer was investigated. First, the transcription factor-based biosensor LysG, from Corynebacterium glutamicum, was adapted for expression in V. natriegens to facilitate the detection of positively charged amino acids. A set of different biosensor variants were constructed and characterized, using the expression of a fluorescent protein as sensor output. After random mutagenesis, one of the LysG-based sensors was used to screen for amino acid producer strains. Here, fluorescence-activated cell sorting enabled the selective sorting of highly fluorescent cells, i.e. potential producer cells. Using this approach, individual L-lysine, L-arginine and L-histidine producers could be obtained producing up to 1 mM of the effector amino acid, extracellularly. Genome sequencing of the producer strains provided insight into the amino acid production metabolism of V. natriegens.

This work demonstrates the successful expression and application of transcription factor-based biosensors in V. natriegens and provides insight into the underlying physiology, forming a solid basis for further development of this promising microbe.

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Vibrio natriegens is a promising new host for biotechnology.

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Transcription factor-based biosensors were expressed in V. natriegens.

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Mutagenesis and screening using FACS provided amino acid producing mutants.

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Genome sequencing revealed several causal mutations leading to amino acid production.

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These results will support further efforts to develop V. natriegens as a production host.

Advances in developing metabolically engineered microbial platforms to produce fourth-generation biofuels and high-value biochemicals

Producing bio-based chemicals is imperative to establish an eco-friendly circular bioeconomy. However, the compromised titer of these biochemicals hampers their commercial implementation. Advances in genetic engineering tools have enabled researchers to develop robust strains producing desired titers of the next-generation biofuels and biochemicals. The native and non-native pathways have been extensively engineered in various host strains via pathway reconstruction and metabolic flux redirection of lipid metabolism and central carbon metabolism to produce myriad biomolecules including alcohols, isoprenoids, hydrocarbons, fatty-acids, and their derivatives. This review has briefly covered the research efforts made during the previous decade to produce advanced biofuels and biochemicals through engineered microbial platforms along with the engineering approaches employed. The efficiency of the various techniques along with their shortcomings is also covered to provide a comprehensive overview of the progress and future directions to achieve higher titer of fourth-generation biofuels and biochemicals while keeping environmental sustainability intact.

The Marburg Collection: A Golden Gate DNA Assembly Framework for Synthetic Biology Applications in Vibrio natriegens

Vibrio natriegens is known as the world's fastest growing organism with a doubling time of less than 10 min. This incredible growth speed empowers V. natriegens as a chassis for synthetic and molecular biology, potentially replacing E. coli in many applications. While first genetic parts have been built and tested for V. natriegens, a comprehensive toolkit containing well-characterized and standardized parts did not exist. To close this gap, we created the Marburg Collection-a highly flexible Golden Gate cloning toolbox optimized for the emerging chassis organism V. natriegens, containing 191 genetic parts. The Marburg Collection overcomes the paradigm of plasmid construction-integrating inserts into a backbone-by enabling the de novo assembly of plasmids from basic genetic parts. This allows users to select the plasmid replication origin and resistance part independently, which is highly advantageous when limited knowledge about the behavior of those parts in the target organism is available. Additional design highlights of the Marburg Collection are novel connector parts, which facilitate modular circuit assembly and, optionally, the inversion of individual transcription units to reduce transcriptional crosstalk in multigene constructs. To quantitatively characterize the genetic parts contained in the Marburg Collection in V. natriegens, we developed a reliable microplate reader measurement workflow for reporter experiments and overcame organism-specific challenges. We think the Marburg Collection with its thoroughly characterized parts will provide a valuable resource for the growing V. natriegens community.

Metabolic engineering of Vibrio natriegens

Vibrio natriegens is emerging as a promising host for biotechnology which is basically due to the remarkable intrinsic properties such as the exceptionally high growth and substrate consumption rates. The facultatively anaerobic marine bacterium possesses a versatile metabolism, is able to utilize a variety of substrates as carbon and energy sources and is easy to handle in the lab. These features initiated the rapid development of genetic tools and resulted in extensive engineering of production strains in the past years. Although recent examples illustrate the potential of V. natriegens for biotechnology, a comprehensive understanding of the metabolism and its regulation is still lacking but essential to exploit the full potential of this bacterium. In this review, we summarize the current knowledge on the physiological traits and the genomic organization, provide an overview of the available genetic engineering tools and recent advances in metabolic engineering of V. natriegens. Finally, we discuss the obstacles which have to be overcome in order to establish V. natriegens as industrial production host.

High-cell-density fed-batch cultivations of Vibrio natriegens

Objectives

With generation times of less than 10 min under optimal conditions, the halophilic Vibrio natriegens is the fastest growing non-pathogenic bacterium isolated so far. The availability of the full genome and genetic engineering tools and its ability to utilize a wide range of carbon sources make V. natriegens an attractive host for biotechnological production processes. However, high-cell-density cultivations, which are desired at industrial-scale have not been described so far.

Results

In this study we report fed-batch cultivations of V. natriegens in deep-well plates and lab-scale bioreactor cultivations at different temperatures in mineral salt medium (MSM). Upon switching from exponential glucose to constant glucose-feeding cell death was induced. Initial NaCl concentrations of 15–18 g L⁻¹ and a temperature reduction from 37 to 30 °C had a positive effect on cell growth. The maximal growth rate in MSM with glucose was 1.36 h⁻¹ with a specific oxygen uptake rate of 22 mmol g_CDW⁻¹ h⁻¹. High biomass yields of up to 55 g L⁻¹ after only 12 h were reached.

Conclusions

The shown fed-batch strategies demonstrate the potential of V. natriegens as a strong producer in industrial biotechnology.

Supplementary Information

The online version of this article (doi:10.1007/s10529-021-03147-5) contains supplementary material, which is available to authorized users.

Increasing ATP turnover boosts productivity of 2,3-butanediol synthesis in Escherichia coli

Background

The alcohol 2,3-butanediol (2,3-BDO) is an important chemical and an Escherichia coli producer strain was recently engineered for bio-based production of 2,3-BDO. However, further improvements are required for realistic applications.

Results

Here we report that enforced ATP wasting, implemented by overexpressing the genes of the ATP-hydrolyzing F₁-part of the ATPase, leads to significant increases of yield and especially of productivity of 2,3-BDO synthesis in an E. coli producer strain under various cultivation conditions. We studied aerobic and microaerobic conditions as well as growth-coupled and growth-decoupled production scenarios. In all these cases, the specific substrate uptake and 2,3-BDO synthesis rate (up to sixfold and tenfold higher, respectively) were markedly improved in the ATPase strain compared to a control strain. However, aerobic conditions generally enable higher productivities only with reduced 2,3-BDO yields while high product yields under microaerobic conditions are accompanied with low productivities. Based on these findings we finally designed and validated a three-stage process for optimal conversion of glucose to 2,3-BDO, which enables a high productivity in combination with relatively high yield. The ATPase strain showed again superior performance and finished the process twice as fast as the control strain and with higher 2,3-BDO yield.

Conclusions

Our results demonstrate the high potential of enforced ATP wasting as a generic metabolic engineering strategy and we expect more applications to come in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01554-x.

Combinatorial metabolic pathway assembly approaches and toolkits for modular assembly

Synthetic Biology is a rapidly growing interdisciplinary field that is primarily built upon foundational advances in molecular biology combined with engineering design principles such as modularity and interoperability. The field considers living systems as programmable at the genetic level and has been defined by the development of new platform technologies and methodological advances. A key concept driving the field is the Design-Build-Test-Learn cycle which provides a systematic framework for building new biological systems. One major application area for synthetic biology is biosynthetic pathway engineering that requires the modular assembly of different genetic regulatory elements and biosynthetic enzymes. In this review we provide an overview of modular DNA assembly and describe and compare the plethora of in vitro and in vivo assembly methods for combinatorial pathway engineering. Considerations for part design and methods for enzyme balancing are also presented, and we briefly discuss alternatives to intracellular pathway assembly including microbial consortia and cell-free systems for biosynthesis. Finally, we describe computational tools and automation for pathway design and assembly and argue that a deeper understanding of the many different variables of genetic design, pathway regulation and cellular metabolism will allow more predictive pathway design and engineering.

Microbial upgrading of acetate into 2,3-butanediol and acetoin by E. coli W

BACKGROUND

Acetate is an abundant carbon source and its use as an alternative feedstock has great potential for the production of fuel and platform chemicals. Acetoin and 2,3-butanediol represent two of these potential platform chemicals.

RESULTS

The aim of this study was to produce 2,3-butanediol and acetoin from acetate in Escherichia coli W. The key strategies to achieve this goal were: strain engineering, in detail the deletion of mixed-acid fermentation pathways E. coli W ΔldhA ΔadhE Δpta ΔfrdA 445_Ediss and the development of a new defined medium containing five amino acids and seven vitamins. Stepwise reduction of the media additives further revealed that diol production from acetate is mediated by the availability of aspartate. Other amino acids or TCA cycle intermediates did not enable growth on acetate. Cultivation under controlled conditions in batch and pulsed fed-batch experiments showed that aspartate was consumed before acetate, indicating that co-utilization is not a prerequisite for diol production. The addition of aspartate gave cultures a start-kick and was not required for feeding. Pulsed fed-batches resulted in the production of 1.43 g l-1 from aspartate and acetate and 1.16 g l-1 diols (2,3-butanediol and acetoin) from acetate alone. The yield reached 0.09 g diols per g acetate, which accounts for 26% of the theoretical maximum.

CONCLUSION

This study for the first time showed acetoin and 2,3-butanediol production from acetate as well as the use of chemically defined medium for product formation from acetate in E. coli. Hereby, we provide a solid base for process intensification and the investigation of other potential products.

Metabolic engineering of Escherichia coli W for isobutanol production on chemically defined medium and cheese whey as alternative raw material

The aim of this study was to establish isobutanol production on chemically defined medium in Escherichia coli. By individually expressing each gene of the pathway, we constructed a plasmid library for isobutanol production. Strain screening on chemically defined medium showed successful production in the robust E. coli W strain, and expression vector IB 4 was selected as the most promising construct due to its high isobutanol yields and efficient substrate uptake. The investigation of different aeration strategies in combination with strain improvement and the implementation of a pulsed fed-batch were key for the development of an efficient production process. E. coli W ΔldhA ΔadhE Δpta ΔfrdA enabled aerobic isobutanol production at 38% of the theoretical maximum. Use of cheese whey as raw material resulted in longer process stability, which allowed production of 20 g l⁻¹ isobutanol. Demonstrating isobutanol production on both chemically defined medium and a residual waste stream, this study provides valuable information for further development of industrially relevant isobutanol production processes.