Enhanced 2,3-butanediol production in fed-batch cultures of free and immobilized Bacillus licheniformis DSM 8785

Metabolic engineering of Paenibacillus polymyxa for effective production of 2,3-butanediol from poplar hydrolysate

2,3-Butanediol is an essential renewable fuel. The synthesis of 2,3-butanediol using Paenibacillus polymyxa has attracted increasing attention. In this study, the glucose-derived 2,3-butanediol pathway and its related genes were identified in P. polymyxa using combined transcriptome and metabolome analyses. The functions of two distinct genes ldh1 and ldh3 encoding lactate dehydrogenase, the gene bdh encoding butanediol dehydrogenase, and the spore-forming genes spo0A and spoIIE were studied and directly knocked out or overexpressed in the genome sequence to improve the production of 2,3-butanediol. A raw hydrolysate of poplar wood containing 27 g/L glucose and 15 g/L xylose was used to produce 2,3-butanediol with a maximum yield of 0.465 g/g and 93 % of the maximum theoretical value, and the total production of 2,3-butanediol and ethanol reached 21.7 g/L. This study provides a new scheme for engineered P. polymyxa to produce renewable fuels using raw poplar wood hydrolysates.

Influence of pH on Inulin Conversion to 2,3-Butanediol by Bacillus licheniformis 24: A Gene Expression Assay

2,3-Butanediol (2,3-BD) is an alcohol highly demanded in the chemical, pharmaceutical, and food industries. Its microbial production, safe non-pathogenic producer strains, and suitable substrates have been avidly sought in recent years. The present study investigated 2,3-BD synthesis by the GRAS Bacillus licheniformis 24 using chicory inulin as a cheap and renewable substrate. The process appears to be pH-dependent. At pH 5.25, the synthesis of 2,3-BD was barely detectable due to the lack of inulin hydrolysis. At pH 6.25, 2,3-BD concentration reached 67.5 g/L with rapid hydrolysis of the substrate but was accompanied by exopolysaccharide (EPS) synthesis. Since inulin conversion by bacteria is a complex process and begins with its hydrolysis, the question of the acting enzymes arose. Genome mining revealed that several glycoside hydrolase (GH) enzymes from different CAZy families are involved. Five genes encoding such enzymes in B. licheniformis 24 were amplified and sequenced: sacA, sacB, sacC, levB, and fruA. Real-time RT-PCR experiments showed that the process of inulin hydrolysis is regulated at the level of gene expression, as four genes were significantly overexpressed at pH 6.25. In contrast, the expression of levB remained at the same level at the different pH values at all-time points. It was concluded that the sacC and sacA/fruA genes are crucial for inulin hydrolysis. They encode exoinulinase (EC 3.2.1.80) and sucrases (EC 3.2.1.26), respectively. The striking overexpression of sacB under these conditions led to increased synthesis of EPS; therefore, the simultaneous production of 2,3-BD and EPS cannot be avoided.

Development of an industrial yeast strain for efficient production of 2,3-butanediol

As part of the transition from a fossil resources-based economy to a bio-based economy, the production of platform chemicals by microbial cell factories has gained strong interest. 2,3-butanediol (2,3-BDO) has various industrial applications, but its production by microbial fermentation poses multiple challenges. We have engineered the bacterial 2,3-BDO synthesis pathway, composed of AlsS, AlsD and BdhA, in a pdc-negative version of an industrial Saccharomyces cerevisiae yeast strain. The high concentration of glycerol caused by the excess NADH produced in the pathway from glucose to 2,3-BDO was eliminated by overexpression of NoxE and also in a novel way by combined overexpression of NDE1, encoding mitochondrial external NADH dehydrogenase, and AOX1, encoding a heterologous alternative oxidase expressed inside the mitochondria. This was combined with strong downregulation of GPD1 and deletion of GPD2, to minimize glycerol production while maintaining osmotolerance. The HGS50 strain produced a 2,3-BDO titer of 121.04 g/L from 250 g/L glucose, the highest ever reported in batch fermentation, with a productivity of 1.57 g/L.h (0.08 g/L.h per gCDW) and a yield of 0.48 g/g glucose or with 96% the closest to the maximum theoretical yield ever reported. Expression of Lactococcus lactis NoxE, encoding a water-forming NADH oxidase, combined with similar genetic modifications, as well as expression of Candida albicans STL1, also minimized glycerol production while maintaining high osmotolerance. The HGS37 strain produced 130.64 g/L 2,3-BDO from 280 g/L glucose, with productivity of 1.58 g/L.h (0.11 g/L.h per gCDW). Both strains reach combined performance criteria adequate for industrial implementation.

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.

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.

Current Advances in Microbial Production of Acetoin and 2,3-Butanediol by Bacillus spp

The growing need for industrial production of bio-based acetoin and 2,3-butanediol (2,3-BD) is due to both environmental concerns, and their widespread use in the food, pharmaceutical, and chemical industries. Acetoin is a common spice added to many foods, but also a valuable reagent in many chemical syntheses. Similarly, 2,3-BD is an indispensable chemical on the platform in the production of synthetic rubber, printing inks, perfumes, antifreeze, and fuel additives. This state-of-the-art review focuses on representatives of the genus Bacillus as prospective producers of acetoin and 2,3-BD. They have the following important advantages: non-pathogenic nature, unpretentiousness to growing conditions, and the ability to utilize a huge number of substrates (glucose, sucrose, starch, cellulose, and inulin hydrolysates), sugars from the composition of lignocellulose (cellobiose, mannose, galactose, xylose, and arabinose), as well as waste glycerol. In addition, these strains can be improved by genetic engineering, and are amenable to process optimization. Bacillus spp. are among the best acetoin producers. They also synthesize 2,3-BD in titer and yield comparable to those of the pathogenic producers. However, Bacillus spp. show relatively lower productivity, which can be increased in the course of challenging future research.

New Exopolysaccharides Produced by Bacillus licheniformis 24 Display Substrate-Dependent Content and Antioxidant Activity

Bacillus licheniformis is a soil bacterium with many industrial applications. In addition to enzymes, platform chemicals, antibiotics and phytohormones, the species produces exopolysaccharides (EPSs) of various biological activities. This study revealed that Bulgarian isolate B. licheniformis 24 produced EPSs consisting of galactose, glucose and mannose with substrate-dependent ratio. From glucose, B. licheniformis 24 secreted EPS1, consisting of 54% galactose, 39% glucose and 7% mannose. From fructose, the strain formed EPS2, containing 51% glucose, 30% mannose and 19% galactose. Batch cultivation in flasks yielded 2.2–2.6 g/L EPS1 and 1.90–2.11 g/L EPS2. Four to five times higher yields of EPS were obtained from both substrates during batch and fed-batch processes in a fermenter at 37.8 °C, pH 6.2 and aeration 3.68 vvm. The batch process with 200 g/L of starting substrates received 9.64 g/L EPS1 and 6.29 g/L EPS2, reaching maximum values at the 33rd and 24th h, respectively. Fed-batch fermentation resulted in the highest yields, 12.61 g/L EPS1 and 7.03 g/L EPS2. In all processes, EPSs were produced only in the exponential growth phase. Both EPSs exhibited antioxidant activity, but EPS2 was much more potent in this regard, reaching 811 μM Vitamin C Equivalent Antioxidant Capacity (versus 135 μM for EPS1). EPS1 displayed antibacterial activity against a non-O1 strain of Vibrio cholerae.

Enhanced Activity by Genetic Complementarity: Heterologous Secretion of Clostridial Cellulases by Bacillus licheniformis and Bacillus velezensis

To adapt to various ecological niches, the members of genus Bacillus display a wide spectrum of glycoside hydrolases (GH) responsible for the hydrolysis of cellulose and lignocellulose. Being abundant and renewable, cellulose-containing plant biomass may be applied as a substrate in second-generation biotechnologies for the production of platform chemicals. The present study aims to enhance the natural cellulase activity of two promising 2,3-butanediol (2,3-BD) producers, Bacillus licheniformis 24 and B. velezensis 5RB, by cloning and heterologous expression of cel8A and cel48S genes of Acetivibrio thermocellus. In B. licheniformis, the endocellulase Cel8A (GH8) was cloned to supplement the action of CelA (GH9), while in B. velezensis, the cellobiohydrolase Cel48S (GH48) successfully complemented the activity of endo-cellulase EglS (GH5). The expression of the natural and heterologous cellulase genes in both hosts was demonstrated by reverse-transcription PCR. The secretion of clostridial cellulases was additionally enhanced by enzyme fusion to the subtilisin-like signal peptide, reaching a significant increase in the cellulase activity of the cell-free supernatants. The results presented are the first to reveal the possibility of genetic complementation for enhancement of cellulase activity in bacilli, thus opening the prospect for genetic improvement of strains with an important biotechnological application.

Highly Efficient 2,3-Butanediol Production by Bacillus licheniformis via Complex Optimization of Nutritional and Technological Parameters

2,3-Butanediol (2,3-BD) is a reagent with remarkable commercial use as a platform chemical in numerous industries. The present study aims to determine the capabilities of non-pathogenic and cellulolytic Bacillus licheniformis 24 as a 2,3-BD producer. By applying the Plackett–Burman design and response surface methodology through central composite design (CCD), a complex optimization of medium and process parameters was conducted. Thus, among ten studied factors of medium content, four components were evaluated with a significant positive effect on 2,3-BD formation. Their optimal values for 2,3-BD production (yeast extract, 13.38 g/L; tryptone, 6.41 g/L; K2HPO4, 4.2 g/L; MgSO4, 0.32 g/L), as well as the optimal temperature (37.8 °C), pH (6.23) and aeration rate (3.68 vvm) were predicted by CCD experiments and validated in a series of batch processes. In optimized batch fermentation of 200 g/L of glucose 91.23 g/L of 2,3-BD was obtained, with the overall productivity of 1.94 g/L/h and yield of 0.488 g/g. To reveal the maximum 2,3-BD tolerance of B. licheniformis 24, fed-batch fermentation was carried out. The obtained 138.8 g/L of 2,3-BD with a yield of 0.479 g/g and productivity of 1.16 g/L/h ranks the strain among the best 2,3-BD producers.

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.

Isolation and identification of an osmotolerant Bacillus amyloliquefaciens strain T4 for 2, 3-butanediol production with tobacco waste

Microbial biomass and waste materials conversion for biochemicals production has been an alternative for energy conservation and emission reduction. While toxic substances in biomass materials and high osmotic pressure formed in fermentation-based systems block the bioconversion processes of microorganisms. In the present study, strain T4 that isolated from tobacco waste could resist toxic inhibitors such as nicotine and was suitable for generation of 2, 3-butanediol (2, 3-BD) with a high concentration of glucose (up to 20%). 30.06 and 1.54 g/L of 2, 3-BD was generated respectively from 50 g/L of tobacco waste with and without 200 g/L glucose after fermentation for 48 h. Besides, the results of biochemical tests showed that it was gram-positive and able to liquefy gelatin, hydrolyze starch and produce catalases. It could utilize glucose but not lactose as carbohydrates during fermentation. The 16S rRNA sequence and systematic analysis revealed that T4 was identified to be a Bacillus amyloliquefaciens (B. amyloliquefaciens). This work presents a promising model microorganism chassis to use the biomass waste for high value-added biochemicals production.

2,3-Butanediol production using soy-based nitrogen source and fermentation process evaluation by a novel isolate of Bacillus licheniformis BL1

2,3-Butanediol (2,3-BDO) has varied applications in chemical, pharmaceutical, & food industry. Microorganisms belonging to Klebsiella, Enterobacter & Serratia genera are well-known producers of 2,3-BDO. However, they have limited usage in industrial-scale owing to their pathogenic nature. A nonpathogenic soil isolate identified as Bacillus licheniformis (BL1) was thus investigated for 2,3-BDO production. Soy flakes, soy flour, defatted soy, and soybean meal-based hydrolysates replaced yeast extract and peptone as nitrogen sources. Defatted soy flakes and soybean meal hydrolysate led to an equivalent 2,3-BDO yield and productivity as compared to that of Yeast Extract and peptone. The pH and oxygen variation influenced the proportion of various products of the mixed acid-butanediol pathway. Further, the batch mode fermentation with soy hydrolysate and optimized process parameter resulted in 2,3-BDO titer, yield and productivity of 11.06 g/L, 0.43 g/g and 0.48 g/L h respectively. Glucose concentration above 5% was inhibitory and led to reduction in the specific growth rate of BL1 in batch cultivation. Intermittent glucose feeding in fed-batch mode overcame this substrate limitation resulting in increased titers (49.8 g/L) and productivity (0.62 g/L h). Modified medium containing soy hydrolysate as nitrogen source with fermentation process optimization resulted in 67% decrease in medium cost for 2,3-BDO production.

Process optimization for mass production of 2,3-butanediol by Bacillus subtilis CS13

BACKGROUND

Bacillus subtilis CS13 was previously isolated for 2,3-butanediol (2,3-BD) and poly-γ-glutamic acid (γ-PGA) co-production. When culturing this strain without L-glutamic acid in the medium, 2,3-BD is the main metabolic product. 2,3-BD is an important substance and fuel with applications in the chemical, food, and pharmaceutical industries. However, the yield and productivity for the B. subtilis strain should be improved for more efficient production of 2,3-BD.

RESULTS

The medium composition, which contained 281.1 g/L sucrose, 21.9 g/L ammonium citrate, and 3.6 g/L MgSO₄·7H₂O, was optimized by response surface methodology for 2,3-BD production using B. subtilis CS13. The maximum amount of 2,3-BD (125.5 ± 3.1 g/L) was obtained from the optimized medium after 96 h. The highest concentration and productivity of 2,3-BD were achieved simultaneously at an agitation speed of 500 rpm and aeration rate of 2 L/min in the batch cultures. A total of 132.4 ± 4.4 g/L 2,3-BD was obtained with a productivity of 2.45 ± 0.08 g/L/h and yield of 0.45 g_2,3-BD/g_sucrose by fed-batch fermentation. The meso-2,3-BD/2,3-BD ratio of the 2,3-BD produced by B. subtilis CS13 was 92.1%. Furthermore, 89.6 ± 2.8 g/L 2,3-BD with a productivity of 2.13 ± 0.07 g/L/h and yield of 0.42 g_2,3-BD/g_sugar was achieved using molasses as a carbon source.

CONCLUSIONS

The production of 2,3-BD by B. subtilis CS13 showed a higher concentration, productivity, and yield compared to the reported generally recognized as safe 2,3-BD producers. These results suggest that B. subtilis CS13 is a promising strain for industrial-scale production of 2,3-BD.

How to outwit nature: Omics insight into butanol tolerance

The energy crisis, depletion of oil reserves, and global climate changes are pressing problems of developed societies. One possibility to counteract that is microbial production of butanol, a promising new fuel and alternative to many petrochemical reagents. However, the high butanol toxicity to all known microbial species is the main obstacle to its industrial implementation. The present state of the art review aims to expound the recent advances in modern omics approaches to resolving this insurmountable to date problem of low butanol tolerance. Genomics, transcriptomics, and proteomics show that butanol tolerance is a complex phenomenon affecting multiple genes and their expression. Efflux pumps, stress and multidrug response, membrane transport, and redox-related genes are indicated as being most important during butanol challenge, in addition to fine-tuning of global regulators of transcription (Spo0A, GntR), which may further improve tolerance. Lipidomics shows that the alterations in membrane composition (saturated lipids and plasmalogen increase) are very much species-specific and butanol-related. Glycomics discloses the pleiotropic effect of CcpA, the role of alternative sugar transport, and the production of exopolysaccharides as alternative routes to overcoming butanol stress. Unfortunately, the strain that simultaneously syntheses and tolerates butanol in concentrations that allow its commercialization has not yet been discovered or produced. Omics insight will allow the purposeful increase of butanol tolerance in natural and engineered producers and the effective heterologous expression of synthetic butanol pathways in strains hereditary butanol-resistant up to 3.2 - 4.9% (w/v). Future breakthrough can be achieved by a detailed study of the membrane proteome, of which 21% are proteins with unknown functions.

Conversion of Xylose from Birch Hemicellulose Hydrolysate to 2,3-Butanediol with Bacillus vallismortis

Biotechnologically produced 2,3-butanediol (2,3-BDO) is a potential starting material for industrial bulk chemicals, such as butadiene or methyl ethyl ketone, which are currently produced from fossil feedstocks. So far, the highest 2,3-BDO concentrations have been obtained with risk class 2 microorganisms and pure glucose as substrate. However, as glucose stays in competition to food and feed industries, a lot of effort has been done in the last years finding efficient alternative substrates. Thereby xylose from hydrolysed wood hemicelluloses is a promising substrate for the production of 2,3-BDO. The risk class 1 microorganism Bacillus vallismortis strain was identified as a very promising 2,3-BDO producer. The strain is able to utilize xylose almost in the same manner as glucose. B. vallismortis is less prone to common inhibiting compounds in lignocellulosic extracts/hydrolysates. When using a concentrated hemicellulose fraction from birch wood hydrolysate, which was produced with ultrafiltration and after which the acetate concentration was reduced, a yield of 0.43 g g−1 was achieved and the xylose consumption and the 2,3-BDO production is basically the same as using pure xylose.

Lignocellulosic bio-refinery approach for microbial 2,3-Butanediol production

Bio-refinery approach using agricultural and industrial waste material as feedstock is becoming a preferred area of interest in biotechnology in the current decades. The reasons for this trend are mainly because of the declining petroleum resources, greenhouse gas emission risks and fluctuating market price of crude oil. Most chemicals synthesized petro chemically, can be produced using microbial biocatalysts. 2,3-Butanediol (BDO) is such an important platform bulk chemical with numerous industrial applications including as a fuel additive. Although microbial production of BDO is well studied, strategies that could successfully upgrade the current lab-scale researches to an industrial level have to be developed. This review presents an overview of the recent trends and developments in the microbial production of BDO from different lignocellulose biomass.

Online monitoring of the respiratory quotient reveals metabolic phases during microaerobic 2,3-butanediol production with Bacillus licheniformis

Microaerobic cultivation conditions are often beneficial for the biotechnological production of reduced metabolites like 2,3-butanediol. However, due to oxygen limitation, process monitoring based on oxygen transfer rate, or dissolved oxygen measurement provides only limited information. In this study, online monitoring of the respiratory quotient is used to investigate the metabolic activity of Bacillus licheniformis DSM 8785 during mixed acid-2,3-butanediol production under microaerobic conditions. Thereby, the respiratory quotient provides valuable information about different metabolic phases. Based on partial reaction stoichiometries, the metabolic activity in each phase of the cultivation was revealed, explaining the course of the respiratory quotient. This provides profound information on the formation or consumption of glucose, 2,3-butanediol, ethanol and lactate, both, in shake flasks and stirred tank reactor cultivations. Furthermore, the average respiratory quotient correlates with the oxygen availability during the cultivation. Carbon mass balancing revealed that this reflects the increased formation of reduced metabolites with increasing oxygen limitation. The results clearly demonstrate that the respiratory quotient is a valuable online signal to reveal and understand the metabolic activity during microaerobic cultivations. The approach of combining respiratory quotient monitoring with stoichiometric considerations can be applied to other organisms and processes to define suitable cultivation conditions to produce the desired product spectrum.

Engineering a newly isolated Bacillus licheniformis strain for the production of (2R,3R)-butanediol

Several microorganisms can produce 2,3-butanediol (BDO), an industrially promising chemical. In this study, a Bacillus licheniformis named as 4071, was isolated from soil sample. It is a GRAS (generally recognized as safe) strain and could over-produce 2,3-BDO. Due to its mucoid forming characteristics, UV-random mutagenesis was carried out to obtain a mucoid-free strain, 4071-15. As a result, capabilities of 4071-15 strain in terms of transformation efficiency of bacillus plasmids (pC194, pUB110, and pUCB129) and fermentation performance were highly upgraded compared to those of the parent strain. In particular, 4071-15 strain could produce 123 g/L of 2,3-BDO in a fed-batch fermentation in which the ratio of (2R,3S)- to (2R,3R)-form isomers was 1:1. To increase the selectivity of (2R,3R)-BDO, budC gene was deleted by using temperature-sensitive gene deletion process via homologous recombination. The 4071-15 △budC mutant strain dramatically increased selectivity of (2R,3R)-BDO to 91% [96.3 g/L of (2R,3R)-BDO and 9.33 g/L of (2R,3S)-BDO], which was 43% higher than that obtained by the parent strain. This study has shown the potential of an isolate for 2,3-BDO production, and that the ratio of 2,3-BDO can be controlled by genetic engineering depending on its industrial usage.

High 2,3-butanediol production from glycerol by Raoultella terrigena CECT 4519

Bioconversion of biodiesel-derived glycerol into 2,3-butanediol has received recently much attention due to its increasing surplus and its multiple uses in industry as bulk chemical. The influence of initial glycerol concentration on 2,3-butanediol production in batch runs has been studied. A concentration higher than 140 g/L produces an inhibitory effect on the final 2,3-butanediol concentration and its production rate. In batch mode, the highest yield respect to the theoretical maximum yield (71%) was reached employing 140 g/L as initial concentration 140 g/L. Based on these results, a high 2,3-butanediol production has been achieved through a fed-batch strategy. The reached 2,3-butanediol concentration was 90.5 g/L from pure glycerol and 80.5 g/L from raw glycerol. The 2,3-butanediol yield respect to the theoretical maximum yield was also improved through the fed-batch operation (90%). To date, this concentration is the highest produced amount employing as biocatalyst a non-pathogenic bacterium (level 1).

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.

Shake flask methodology for assessing the influence of the maximum oxygen transfer capacity on 2,3-butanediol production

BACKGROUND

Production of 2,3-butanediol from renewable resources is a promising measure to decrease the consumption of fossil resources in the chemical industry. One of the most influential parameters on biotechnological 2,3-butanediol production is the oxygen availability during the cultivation. As 2,3-butanediol is produced under microaerobic process conditions, a well-controlled oxygen supply is the key parameter to control biomass formation and 2,3-butanediol production. As biomass is on the one hand not the final product, but on the other hand the essential biocatalyst, the optimal compromise between biomass formation and 2,3-butanediol production has to be defined.

RESULTS

A shake flask methodology is presented to evaluate the effects of oxygen availability on 2,3-butanediol production with Bacillus licheniformis DSM 8785 by variation of the filling volume. A defined two-stage cultivation strategy was developed to investigate the metabolic response to different defined maximum oxygen transfer capacities at equal initial growth conditions. The respiratory quotient was measured online to determine the point of glucose depletion, as 2,3-butanediol is consumed afterwards. Based on this strategy, comparable results to stirred tank reactors were achieved. The highest space-time yield (1.3 g/L/h) and a 2,3-butanediol concentration of 68 g/L combined with low acetoin concentrations and avoided glycerol formation were achieved at a maximum oxygen transfer capacity of 13 mmol/L/h. The highest overall 2,3-butanediol concentration of 78 g/L was observed at a maximum oxygen transfer capacity of 4 mmol/L/h.

CONCLUSIONS

The presented shake flask approach reduces the experimental effort and costs providing a fast and reliable methodology to investigate the effects of oxygen availability. This can be applied especially on product and by-product formation under microaerobic conditions. Utilization of the maximum oxygen transfer capacity as measure for the oxygen availability allows for an easy adaption to other bioreactor setups and scales.

Bioconversion of pentose sugars to value added chemicals and fuels: Recent trends, challenges and possibilities

Most of the crop plants contain about 30% of hemicelluloses comprising D-xylose and D-arabinose. One of the major limitation for the use of pentose sugars is that high purity grade D-xylose and D-arabinose are yet to be produced as commodity chemicals. Research and developmental activities are going on in this direction for their use as platform intermediates through economically viable strategies. During chemical pretreatment of biomass, the pentose sugars were generated in the liquid stream along with other compounds. This contains glucose, proteins, phenolic compounds, minerals and acids other than pentose sugars. Arabinose is present in small amounts, which can be used for the economic production of value added compound, xylitol. The present review discusses the recent trends and developments as well as challenges and opportunities in the utilization of pentose sugars generated from lignocellulosic biomass for the production of value added compounds.

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.

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.

Effect of oxygen mass transfer rate on the production of 2,3-butanediol from glucose and agro-industrial byproducts by Bacillus licheniformis ATCC9789

BACKGROUND

2,3-Butanediol (BD) is a largely used fossil-based platform chemical. The yield and productivity of bio-based BD fermentative production must be increased and cheaper substrates need to be identified, to make bio-based BD production more competitive. As BD bioproduction occurs under microaerobic conditions, a fine tuning and control of the oxygen transfer rate (OTR) is crucial to maximize BD yield and productivity. Very few studies on BD bioproduction focused on the use of non-pathogenic microorganisms and of byproducts as substrate. The goal of this work was to optimize BD bioproduction by the non-pathogenic strain Bacillus licheniformis ATCC9789 by (i) identifying the ranges of volumetric and biomass-specific OTR that maximize BD yield and productivity using standard sugar and protein sources, and (ii) performing a preliminary evaluation of the variation in process performances and cost resulting from the replacement of glucose with molasses, and beef extract/peptone with chicken meat and bone meal, a byproduct of the meat production industry.

RESULTS

OTR optimization with an expensive, standard medium containing glucose, beef extract and peptone revealed that OTRs in the 7-15 mmol/L/h range lead to an optimal BD yield (0.43 ± 0.03 g/g) and productivity (0.91 ± 0.05 g/L/h). The corresponding optimal range of biomass-specific OTR was equal to 1.4-7.9 [Formula: see text], whereas the respiratory quotient ranged from 1.8 to 2.5. The switch to an agro-industrial byproduct-based medium containing chicken meat and bone meal and molasses led to a 50% decrease in both BD yield and productivity. A preliminary economic analysis indicated that the use of the byproduct-based medium can reduce by about 45% the BD production cost.

CONCLUSIONS

A procedure for OTR optimization was developed and implemented, leading to the identification of a range of biomass-specific OTR and respiratory quotient to be used for the scale-up and control of BD bioproduction by Bacillus licheniformis. The switch to a byproduct-based medium led to a relevant decrease in BD production cost. Further research is needed to optimize the process of BD bioproduction from the tested byproduct-based medium.

Enhancement of 2,3-butanediol production from Jerusalem artichoke tuber extract by a recombinant Bacillus sp. strain BRC1 with increased inulinase activity

A Bacillus sp. strain named BRC1 is capable of producing 2,3-butanediol (2,3-BD) using hydrolysates of the Jerusalem artichoke tuber (JAT), a rich source of the fructose polymer inulin. To enhance 2,3-BD production, we undertook an extensive analysis of the Bacillus sp. BRC1 genome, identifying a putative gene (sacC) encoding a fructan hydrolysis enzyme and characterizing the activity of the resulting recombinant protein expressed in and purified from Escherichia coli. Introduction of the sacC gene into Bacillus sp. BRC1 using an expression vector increased enzymatic activity more than twofold. Consistent with this increased enzyme expression, 2,3-BD production from JAT was also increased from 3.98 to 8.10 g L−1. Fed-batch fermentation of the recombinant strain produced a maximal level of 2,3-BD production of 28.6 g L−1, showing a high theoretical yield of 92.3%.

Products Components: Alcohols

Alcohols (C_nH_n+2OH) are classified into primary, secondary, and tertiary alcohols, which can be branched or unbranched. They can also feature more than one OH-group (two OH-groups = diol; three OH-groups = triol). Presently, except for ethanol and sugar alcohols, they are mainly produced from fossil-based resources, such as petroleum, gas, and coal. Methanol and ethanol have the highest annual production volume accounting for 53 and 91 million tons/year, respectively. Most alcohols are used as fuels (e.g., ethanol), solvents (e.g., butanol), and chemical intermediates.This chapter gives an overview of recent research on the production of short-chain unbranched alcohols (C1-C5), focusing in particular on propanediols (1,2- and 1,3-propanediol), butanols, and butanediols (1,4- and 2,3-butanediol). It also provides a short summary on biobased higher alcohols (>C5) including branched alcohols.

Screening of novel bacteria for the 2,3-butanediol production

Biotechnologically produced 2,3-butanediol (2,3-BDO) is a potential starting material for industrial bulk chemicals such as butadiene or methyl ethyl ketone which are currently produced from fossil feedstocks. So far, the highest 2,3-BDO concentrations have been obtained with risk group 2 microorganisms. In this study, three risk group 1 microorganisms are presented that are so far unknown for an efficient production of 2,3-BDO. The strains Bacillus atrophaeus NRS-213, Bacillus mojavensis B-14698, and Bacillus vallismortis B-14891 were evaluated regarding their ability to produce high 2,3-BDO concentrations with a broad range of different carbon sources. A maximum 2,3-BDO concentration of 60.4 g/L was reached with the strain B. vallismortis B-14891 with an initial glucose concentration of 200 g/L within 55 h in a batch cultivation. Besides glucose, B. vallismortis B-14891 converts 14 different substrates that can be obtained from residual biomass sources to 2,3-BDO. Therefore B. vallismortis B-14891 is a promising candidate for the large-scale production of 2,3-BDO with low-cost substrates.

Techno-economic evaluation of a complete bioprocess for 2,3-butanediol production from renewable resources

This study presents the techno-economic evaluation of 2,3-butanediol (BDO) production via fermentation using glycerol, sucrose and sugarcane molasses as carbon sources. Literature-cited experimental data were used to design the fermentation stage, whereas downstream separation of BDO was based on reactive extraction of BDO employing an aldehyde to convert BDO into an acetal that is immiscible with water. The selected downstream process can be used in all fermentations employed. Sensitivity analysis was carried out targeting the estimation of the minimum selling price (MSP) of BDO at different plant capacities and raw material purchase costs. In all cases, the MSP of BDO is higher than 1 $/kg that is considered as the target in order to characterize a fermentation product as platform chemical. The complex nutrient supplements, the raw material market price and the fermentation efficiency were identified as the major reasons for the relatively high MSP observed.

Engineering Bacillus licheniformis for the production of meso-2,3-butanediol

BACKGROUND

2,3-Butanediol (2,3-BD) can be used as a liquid fuel additive to replace petroleum oil, and as an important platform chemical in the pharmaceutical and plastic industries. Microbial production of 2,3-BD by Bacillus licheniformis presents potential advantages due to its GRAS status, but previous attempts to use this microorganism as a chassis strain resulted in the production of a mix of D-2,3-BD and meso-2,3-BD isomers.

RESULTS

The aim of this work was to develop an engineered strain of B. licheniformis suited to produce the high titers of the pure meso-2,3-BD isomer. Glycerol dehydrogenase (Gdh) was identified as the catalyst for D-2,3-BD biosynthesis from its precursor acetoin in B. licheniformis. The gdh gene was, therefore, deleted from the wild-type strain WX-02 to inhibit the flux of acetoin to D-2,3-BD biosynthesis. The acoR gene involved in acetoin degradation through AoDH ES was also deleted to provide adequate flux from acetoin towards meso-2,3-BD. By re-directing the carbon flux distribution, the double-deletion mutant WX-02ΔgdhΔacoR produced 28.2 g/L of meso-2,3-BD isomer with >99 % purity. The titer was 50 % higher than that of the wide type. A bench-scale fermentation by the double-deletion mutant was developed to further improve meso-2,3-BD production. In a fed-batch fermentation, meso-2,3-BD titer reached 98.0 g/L with a purity of >99.0 % and a productivity of 0.94 g/L-h.

CONCLUSIONS

This work demonstrates the potential of producing meso-2,3-BD with high titer and purity through metabolic engineering of B. licheniformis.

Application of enzymatic apple pomace hydrolysate to production of 2,3-butanediol by alkaliphilic Bacillus licheniformis NCIMB 8059

2,3-Butanediol (2,3-BD) synthesis by a nonpathogenic bacterium Bacillus licheniformis NCIMB 8059 from enzymatic hydrolysate of depectinized apple pomace and its blend with glucose was studied. In shake flasks, the maximum diol concentration in fed-batch fermentations was 113 g/L (in 163 h, from the hydrolysate, feedings with glucose) while in batch processes it was around 27 g/L (in 32 h, from the hydrolysate and glucose blend). Fed-batch fermentations in the 0.75 and 30 L fermenters yielded 87.71 g/L 2,3-BD in 160 h, and 72.39 g/L 2,3-BD in 94 h, respectively (from the hydrolysate and glucose blend, feedings with glucose). The hydrolysate of apple pomace, which was for the first time used for microbial 2,3-BD production is not only a source of sugars but also essential minerals.

Cloning, Expression, and Characterization of budC Gene Encoding meso-2,3-Butanediol Dehydrogenase from Bacillus licheniformis

The budC gene encoding a meso-2,3-butanediol dehydrogenase (BlBDH) from Bacillus licheniformis was cloned and overexpressed in Escherichia coli BL21(DE3). Sequence analysis reveals that this BlBDH belongs to short-chain dehydrogenase/reductase (SDR) superfamily. In the presence of NADH, BlBDH catalyzes the reduction of diacetyl to (3S)-acetoin (97.3% ee), and further to (2S,3S)-2,3-butanediol (97.3% ee and 96.5% de). Similar to other meso-2,3-BDHs, it shows oxidative activity to racemic 2,3-butanediol whereas no activity toward racemic acetoin in the presence of NAD(+). For diacetyl reduction and 2,3-butanediol oxidation, the pH optimum of BlBDH is 5.0 and 10.0, respectively. Unusually, it shows relatively high activity over a wide pH range from 5.0 to 8.0 for racemic acetoin reduction. BlBDH shows lower K m and higher catalytic efficiency toward racemic acetoin (K m = 0.47 mM, k cat /K m = 432 s(-1)·mM(-1)) when compared with 2,3-butanediol (K m = 7.25 mM, k cat /K m = 81.5 s(-1)·mM(-1)), indicating its physiological role in favor of reducing racemic acetoin into 2,3-butanediol. The enzymatic characterization of BlBDH provides evidence for the directed engineering of B. licheniformis for producing enantiopure 2,3-butanediol.