Enhanced 2,3-butanediol production by addition of acetic acid in Paenibacillus polymyxa

Bioengineering for the industrial production of 2,3-butanediol by the yeast, Saccharomyces cerevisiae

Owing to issues, such as the depletion of petroleum resources and price instability, the development of biorefinery related technologies that produce fuels, electric power, chemical substances, among others, from renewable resources is being actively promoted. 2,3-Butanediol (2,3-BDO) is a key compound that can be used to produce various chemical substances. In recent years, 2,3-BDO production using biological processes has attracted extensive attention for achieving a sustainable society through the production of useful compounds from renewable resources. With the development of genetic engineering, metabolic engineering, synthetic biology, and other research field, studies on 2,3-BDO production by the yeast, Saccharomyces cerevisiae, which is safe and can be fabricated using an established industrial-scale cultivation technology, have been actively conducted. In this review, we sought to describe 2,3-BDO and its derivatives; discuss 2,3-BDO production by microorganisms, in particular S. cerevisiae, whose research and development has made remarkable progress; describe a method for separating and recovering 2,3-BDO from a microbial culture medium; and propose future prospects for the industrial production of 2,3-BDO by microorganisms.

Inactivation of the Levansucrase Gene in Paenibacillus polymyxa DSM 365 Diminishes Exopolysaccharide Biosynthesis during 2,3-Butanediol Fermentation

The formation of exopolysaccharides (EPSs) during 2,3-butanediol (2,3-BD) fermentation by Paenibacillus polymyxa increases medium viscosity, which in turn presents considerable technical and economic challenges to 2,3-BD downstream processing. To eliminate EPS production during 2,3-BD fermentation, we used homologous recombination to disable the EPS biosynthetic pathway in P. polymyxa The gene which encodes levansucrase, the major enzyme responsible for EPS biosynthesis in P. polymyxa, was successfully disrupted. The P. polymyxa levansucrase null mutant produced 2.5 ± 0.1 and 1.2 ± 0.2 g/liter EPS on sucrose and glucose, respectively, whereas the wild type produced 21.7 ± 2.5 and 3.1 ± 0.0 g/liter EPS on the same substrates, respectively. These levels of EPS translate to 8.7- and 2.6-fold decreases in EPS formation by the levansucrase null mutant on sucrose and glucose, respectively, relative to that by the wild type, with no significant reduction in 2,3-BD production. Inactivation of EPS biosynthesis led to a considerable increase in growth. On glucose and sucrose, the cell biomass of the levansucrase null mutant (8.1 ± 0.8 and 6.5 ± 0.3 g/liter, respectively) increased 1.4-fold compared to that of the wild type (6.0 ± 0.1 and 4.6 ± 0.3 g/liter, respectively) grown on the same substrates. Evaluation of the genetic stability of the levansucrase null mutant showed that it remained genetically stable over fifty generations, with no observable decrease in growth or 2,3-BD formation, with or without antibiotic supplementation. Hence, the P. polymyxa levansucrase null mutant has potential for use as an industrial biocatalyst for a cost-effective large-scale 2,3-BD fermentation process devoid of EPS-related challenges.IMPORTANCE Given the current barrage of attention and research investments toward the production of next-generation fuels and chemicals, of which 2,3-butanediol (2,3-BD) produced by nonpathogenic Paenibacillus species is perhaps one of the most vigorously pursued, tools for engineering Paenibacillus species are intensely sought after. Exopolysaccharide (EPS) production during 2,3-BD fermentation constitutes a problem during downstream processing. Specifically, EPS negatively impacts 2,3-BD separation from the fermentation broth, thereby increasing the overall cost of 2,3-BD production. The results presented here demonstrate that inactivation of the levansucrase gene in P. polymyxa leads to diminished EPS accumulation. Additionally, a new method for an EPS assay and a simple protocol employing protoplasts for enhanced transformation of P. polymyxa were developed. Overall, although our study shows that levan is not the only EPS produced by P. polymyxa, it represents a significant first step toward developing cost-effective 2,3-BD fermentation devoid of EPS-associated complications during downstream processing.

The current strategies and parameters for the enhanced microbial production of 2,3-butanediol

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2,3-Butanediol (2,3-BD) is a propitious compound with many industrial uses.

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2,3-BD production has always been hampered by low fermentation yields and high production costs.

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2,3-BD production may be enhanced by optimization of culture conditions and use of high-producing strains.

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TMetabolic engineering tools are currently used to generate high-yielding strains.

2,3-Butanediol (2,3-BD) is a propitious compound with many industrial uses ranging from rubber, fuels, and cosmetics to food additives. Its microbial production has especially attracted as an alternative way to the petroleum-based production. However, 2,3-BD production has always been hampered by low yields and high production costs. The enhanced production of 2,3-butanediol requires screening of the best strains and a systematic optimization of fermentation conditions. Moreover, the metabolic pathway engineering is essential to achieve the best results and minimize the production costs by rendering the strains to use efficiently low cost substrates. This review is to provide up-to-date information on the current strategies and parameters for the enhanced microbial production of 2,3-BD.

Microbial production of 2,3-butanediol for industrial applications

2,3-Butanediol (2,3-BD) has great potential for diverse industries, including chemical, cosmetics, agriculture, and pharmaceutical areas. However, its industrial production and usage are limited by the fairly high cost of its petro-based production. Several bio-based 2,3-BD production processes have been developed and their economic advantages over petro-based production process have been reported. In particular, many 2,3-BD-producing microorganisms including bacteria and yeast have been isolated and metabolically engineered for efficient production of 2,3-BD. In addition, several fermentation processes have been tested using feedstocks such as starch, sugar, glycerol, and even lignocellulose as raw materials. Since separation and purification of 2,3-BD from fermentation broth account for the majority of its production cost, cost-effective processes have been simultaneously developed. The construction of a demonstration plant that can annually produce around 300 tons of 2,3-BD is scheduled to be mechanically completed in Korea in 2019. In this paper, core technologies for bio-based 2,3-BD production are reviewed and their potentials for use in the commercial sector are discussed.

Enhanced 2,3-Butanediol Production by Optimizing Fermentation Conditions and Engineering Klebsiella oxytoca M1 through Overexpression of Acetoin Reductase

Microbial production of 2,3-butanediol (2,3-BDO) has been attracting increasing interest because of its high value and various industrial applications. In this study, high production of 2,3-BDO using a previously isolated bacterium Klebsiella oxytoca M1 was carried out by optimizing fermentation conditions and overexpressing acetoin reductase (AR). Supplying complex nitrogen sources and using NaOH as a neutralizing agent were found to enhance specific production and yield of 2,3-BDO. In fed-batch fermentations, 2,3-BDO production increased with the agitation speed (109.6 g/L at 300 rpm vs. 118.5 g/L at 400 rpm) along with significantly reduced formation of by-product, but the yield at 400 rpm was lower than that at 300 rpm (0.40 g/g vs. 0.34 g/g) due to acetoin accumulation at 400 rpm. Because AR catalyzing both acetoin reduction and 2,3-BDO oxidation in K. oxytoca M1 revealed more than 8-fold higher reduction activity than oxidation activity, the engineered K. oxytoca M1 overexpressing the budC encoding AR was used in fed-batch fermentation. Finally, acetoin accumulation was significantly reduced by 43% and enhancement of 2,3-BDO concentration (142.5 g/L), yield (0.42 g/g) and productivity (1.47 g/L/h) was achieved compared to performance with the parent strain. This is by far the highest titer of 2,3-BDO achieved by K. oxytoca strains. This notable result could be obtained by finding favorable fermentation conditions for 2,3-BDO production as well as by utilizing the distinct characteristic of AR in K. oxytoca M1 revealing the nature of reductase.

Enhanced 2,3-butanediol production from biodiesel-derived glycerol by engineering of cofactor regeneration and manipulating carbon flux in Bacillus amyloliquefaciens

BACKGROUND

Bacillus amyloliquefaciens B10-127 exhibited an excellent ability for industrial-scale microbial fermentation of 2,3-butanediol (2,3-BD) from biodiesel-derived glycerol. However, the accumulation of by-products (acetoin, acetoin, lactate and succinate) and the 2,3-BD yield remains prohibitively low for commercial production.

RESULTS

Several strategies were developed to manipulate the carbon flux to 2,3-BD branch in a designed B. amyloliquefaciens. Firstly, extra copies of NADH/NAD(+) regeneration system were introduced into B. amyloliquefaciens by co-overproduction of glycerol dehydrogenase and acetoin reductase, which resulting in improvement of 2,3-BD production and suppression of by-products accumulation. Subsequently, the transcriptional regulator ALsR under the control of a moderate promoter PbdhA was introduced into B. amyloliquefaciens, which increased carbon flux to 2,3-BD branch. Finally, a three-stage dissolved oxygen control strategy were proposed based on analysis of the characteristic of 2,3-BD fermentation, and a two-stage pH control strategy were proposed based on different pH preferences of ACR for reduction and oxidation. Following these strategies, a high titer (102.3 g/L), yield (0.44 g/g), and productivity (1.16 g/L/h) of 2,3-BD were achieved.

CONCLUSIONS

To our knowledge, this is the highest reported 2,3-BD production using biodiesel-derived glycerol as substrate, and this designed B. amyloliquefaciens should be an excellent candidate for producing 2,3-BD on an industrial scale.

Characterization of acetoin production in a budC gene disrupted mutant of Serratia marcescens G12

The 2,3-butanediol (2,3-BD) dehydrogenase gene budC of Serratia marcescens G12 was disrupted to construct the acetoin (AC) producing strain G12M. In shake-flask cultures, AC production was enhanced by increased concentrations of glucose or sodium acetate in G12M. In fed-batch fermentation, G12M produced 47.5 g/L AC along with 9.8 g/L 2,3-BD. The expression of the key enzymes for AC synthesis was further investigated. Alpha-acetolactate synthase gene budB decreased its expression significantly in G12M compared with G12. This probably explained the moderate AC production in G12M cultures. Additionally, overexpression of budB gene and α-acetolactate decarboxylase gene budA was conducted in G12M and no significant increase of AC was observed. The results suggested that intracellular AC accumulation might inhibit the expression of budB and budA gene and induce budC gene expression in G12M. Our analyses offered the bases for further genetic manipulations in improving AC production in microbial fermentations.

Induced resistance by a long-chain bacterial volatile: elicitation of plant systemic defense by a C13 volatile produced by Paenibacillus polymyxa

Background

Some strains of plant growth-promoting rhizobacteria (PGPR) elicit induced systemic resistance (ISR) by emission of volatile organic compounds (VOCs) including short chain alcohols, acetoin, and 2,3-butanediol. The objective of this study was to evaluate whether species-specific VOCs from PGPR strain Paenibacillus polymyxa E681 can promote growth and induce resistance in Arabidopsis.

Methodology/Principal Findings

The efficacy of induction was strain-specific, with stronger protection against Pseudomonas syringae pv. maculicola ES4326 in plants exposed to VOCs from P. polymyxa E681 versus Arabidopsis plants exposed to VOCs from a reference strain Bacillus subtilis GB03, which was previously shown to elicit ISR and plant growth promotion. VOC emissions released from E681 primed transcriptional expression of the salicylic acid, jasmonic acid, and ethylene signaling marker genes PR1, ChiB, and VSP2, respectively. In addition, strain E681 produced more than thirty low molecular-weight VOCs, of which tridecane was only produced by E681 and not found in GB03 or IN937a volatile blends. These strain-specific VOCs induced PR1 and VSP2 genes.

Conclusions/Significance

These results provide new insight into the existence of a long chain VOC signaling molecule produced by P. polymyxa that can serve as a bacterial trigger of induced systemic resistance in planta.

Novel (2R,3R)-2,3-butanediol dehydrogenase from potential industrial strain Paenibacillus polymyxa ATCC 12321

A (2R,3R)-2,3-butanediol dehydrogenase (BDH99::67) from Paenibacillus polymyxa ATCC 12321 was functionally characterized. The genetic characteristics of BDH99::67 are completely different from those of meso- and (2S,3S)-2,3-butanediol dehydrogenases. The results showed that BDH99::67 belongs to the medium-chain dehydrogenase/reductase superfamily and not to the short-chain dehydrogenase/reductase superfamily, to which meso- and (2S,3S)-2,3-butanediol dehydrogenases belong.

Enhancement of 2,3-butanediol production by Klebsiella oxytoca PTCC 1402

Optimal operating parameters of 2,3-Butanediol production using Klebsiella oxytoca under submerged culture conditions are determined by using Taguchi method. The effect of different factors including medium composition, pH, temperature, mixing intensity, and inoculum size on 2,3-butanediol production was analyzed using the Taguchi method in three levels. Based on these analyses the optimum concentrations of glucose, acetic acid, and succinic acid were found to be 6, 0.5, and 1.0 (% w/v), respectively. Furthermore, optimum values for temperature, inoculum size, pH, and the shaking speed were determined as 37°C, 8 (g/L), 6.1, and 150 rpm, respectively. The optimal combinations of factors obtained from the proposed DOE methodology was further validated by conducting fermentation experiments and the obtained results revealed an enhanced 2,3-Butanediol yield of 44%.

Ecology and biotechnological potential of Paenibacillus polymyxa: a minireview

Microbial diversity is a major resource for biotechnological products and processes. Bacteria are the most dominant group of this diversity which produce a wide range of products of industrial significance. Paenibacillus polymyxa (formerly Bacillus polymyxa), a non pathogenic and endospore-forming Bacillus, is one of the most industrially significant facultative anaerobic bacterium. It occurs naturally in soil, rhizosphere and roots of crop plants and in marine sediments. During the last two decades, there has been a growing interest for their ecological and biotechnological importance, despite their limited genomic information. P. polymyxa has a wide range of properties, including nitrogen fixation, plant growth promotion, soil phosphorus solubilisation and production of exopolysaccharides, hydrolytic enzymes, antibiotics, cytokinin. It also helps in bioflocculation and in the enhancement of soil porosity. In addition, it is known to produce optically active 2,3-butanediol (BDL), a potentially valuable chemical compound from a variety of carbohydrates. The present review article aims to provide an overview of the various roles that these microorganisms play in the environment and their biotechnological potential.

Response of the cytoplasmic and membrane proteome of Corynebacterium glutamicum ATCC 13032 to pH changes

Background

C. glutamicum has traditionally been grown in neutral-pH media for amino acid production, but in a previous article we reported that this microorganism is a moderate alkaliphile since it grows optimally at pH 7.0–9.0, as shown in fermentor studies under tightly controlled pH conditions. We determined the best pH values to study differential expression of several genes after acidic or basic pH conditions (pH 6.0 for acidic expression and pH 9.0 for alkaline expression). Thus, it was interesting to perform a detailed analysis of the pH-adaptation response of the proteome of C. glutamicum ATCC 13032 to clarify the circuits involved in stress responses in this bacterium. In this paper we used the above indicated pH conditions, based on transcriptional studies, to confirm that pH adaptation results in significant changes in cytoplasmatic and membrane proteins.

Results

The cytoplasmatic and membrane proteome of Corynebacterium glutamicum ATCC 13032 at different pH conditions (6.0, 7.0 and 9.0) was analyzed by classical 2D-electrophoresis, and by anion exchange chromatography followed by SDS-PAGE (AIEC/SDS-PAGE). A few cytoplasmatic proteins showed differential expression at the three pH values with the classical 2D-technique including a hypothetical protein cg2797, L-2.3-butanediol dehydrogenase (ButA), and catalase (KatA). The AIEC/SDS-PAGE technique revealed several membrane proteins that respond to pH changes, including the succinate dehydrogenase complex (SdhABCD), F₀F₁-ATP synthase complex subunits b, α and δ (AtpF, AtpH and AtpA), the nitrate reductase II α subunit (NarG), and a hypothetical secreted/membrane protein cg0752. Induction of the F₀F₁-ATP synthase complex β subunit (AtpD) at pH 9.0 was evidenced by Western analysis. By contrast, L-2.3-butanediol dehydrogenase (ButA), an ATPase with chaperone activity, the ATP-binding subunit (ClpC) of an ATP-dependent protease complex, a 7 TMHs hypothetical protein cg0896, a conserved hypothetical protein cg1556, and the dihydrolipoamide acyltransferase SucB, were clearly up-regulated at pH 6.0.

Conclusion

The observed protein changes explain the effect of the extracellular pH on the growth and physiology of C. glutamicum. Some of the proteins up-regulated at alkaline pH respond also to other stress factors suggesting that they serve to integrate the cell response to different stressing conditions.