Production of 2,3-butanediol from glucose byBacillus licheniformis

Fermentative production of 2,3-Butanediol using bread waste - A green approach for sustainable management of food waste

Bread is Europe's most wasted food, and the second most wasted food after potatoes in UK. Bread waste (BW) is a clean source of high-quality fermentable sugars. In this study, the potential of Enterobacter ludwigii to accumulate 2,3-butanediol (BDO) from BW was evaluated. Initially, the optimal inoculum size and yeast extract concentration were determined, followed by extraction of sugars from BW using acid and enzymatic hydrolysis. A glucose yield of 330-530 g/kg BW was obtained, and the sugars released were utilised for BDO production by E. ludwigii. The fed-batch cultivation using pure glucose and glucose rich hydrolysates from acid and enzymatic hydrolysis resulted in BDO titres of 144.5, 135.4, and 138.8 g/L, after 96 h, with yield of 0.47, 0.42 and 0.48 g/g yield, respectively. The innovation of the work is valorisation of BW to BDO with a circular biorefining approach and thus, reducing BW disposal and associated environmental burden.

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.

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.

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.

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.

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.

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.

Genomics and prevalence of bacterial and archaeal isolates from biogas-producing microbiomes

BACKGROUND

To elucidate biogas microbial communities and processes, the application of high-throughput DNA analysis approaches is becoming increasingly important. Unfortunately, generated data can only partialy be interpreted rudimentary since databases lack reference sequences.

RESULTS

Novel cellulolytic, hydrolytic, and acidogenic/acetogenic Bacteria as well as methanogenic Archaea originating from different anaerobic digestion communities were analyzed on the genomic level to assess their role in biomass decomposition and biogas production. Some of the analyzed bacterial strains were recently described as new species and even genera, namely Herbinix hemicellulosilytica T3/55^T, Herbinix luporum SD1D^T, Clostridium bornimense M2/40^T, Proteiniphilum saccharofermentans M3/6^T, Fermentimonas caenicola ING2-E5B^T, and Petrimonas mucosa ING2-E5A^T. High-throughput genome sequencing of 22 anaerobic digestion isolates enabled functional genome interpretation, metabolic reconstruction, and prediction of microbial traits regarding their abilities to utilize complex bio-polymers and to perform specific fermentation pathways. To determine the prevalence of the isolates included in this study in different biogas systems, corresponding metagenome fragment mappings were done. Methanoculleus bourgensis was found to be abundant in three mesophilic biogas plants studied and slightly less abundant in a thermophilic biogas plant, whereas Defluviitoga tunisiensis was only prominent in the thermophilic system. Moreover, several of the analyzed species were clearly detectable in the mesophilic biogas plants, but appeared to be only moderately abundant. Among the species for which genome sequence information was publicly available prior to this study, only the species Amphibacillus xylanus, Clostridium clariflavum, and Lactobacillus acidophilus are of importance for the biogas microbiomes analyzed, but did not reach the level of abundance as determined for M. bourgensis and D. tunisiensis.

CONCLUSIONS

Isolation of key anaerobic digestion microorganisms and their functional interpretation was achieved by application of elaborated cultivation techniques and subsequent genome analyses. New isolates and their genome information extend the repository covering anaerobic digestion community members.

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.

Improvement of 2,3-butanediol yield in Klebsiella pneumoniae by deletion of the pyruvate formate-lyase gene

Klebsiella pneumoniae is considered a good host strain for the production of 2,3-butanediol, which is a promising platform chemical with various industrial applications. In this study, three genes, including those encoding glucosyltransferase (wabG), lactate dehydrogenase (ldhA), and pyruvate formate-lyase (pflB), were disrupted in K. pneumoniae to reduce both its pathogenic characteristics and the production of several by-products. In flask cultivation with minimal medium, the yield of 2,3-butanediol from rationally engineered K. pneumoniae (ΔwabG ΔldhA ΔpflB) reached 0.461 g/g glucose, which was 92.2% of the theoretical maximum, with a significant reduction in by-product formation. However, the growth rate of the pflB mutant was slightly reduced compared to that of its parental strain. Comparison with similar mutants of Escherichia coli suggested that the growth defect of pflB-deficient K. pneumoniae was caused by redox imbalance rather than reduced level of intracellular acetyl coenzyme A (acetyl-CoA). From an analysis of the transcriptome, it was confirmed that the removal of pflB from K. pneumoniae significantly repressed the expression of genes involved in the formate hydrogen lyase (FHL) system.

A newly isolated Bacillus licheniformis strain thermophilically produces 2,3-butanediol, a platform and fuel bio-chemical

BACKGROUND

2,3-Butanediol (2,3-BD), a platform and fuel bio-chemical, can be efficiently produced by Klebsiella pneumonia, K. oxytoca, and Serratia marcescens. However, these strains are opportunistic pathogens and not favorable for industrial application. Although some generally regarded as safe (GRAS) microorganisms have been isolated in recent years, there is still a demand for safe 2,3-BD producing strains with high productivity and yield under thermophilic fermentation.

RESULTS

Bacillus licheniformis strain 10-1-A was newly isolated for 2,3-BD production. The optimum temperature and medium pH were 50°C and pH 7.0 for 2,3-BD production by strain 10-1-A. The medium composition was optimized through Plackett-Burman design and response surface methodology techniques. With a two-stage agitation speed control strategy, 115.7 g/L of 2,3-BD was obtained from glucose by fed-batch fermentation in a 5-L bioreactor with a high productivity (2.4 g/L·h) and yield (94% of its theoretical value). The 2,3-BD produced by strain 10-1-A comprises (2R,3R)-2,3-BD and meso-2,3-BD with a ratio of nearly 1:1. The bdh and gdh genes encoding meso-2,3-butanediol dehydrogenase (meso-BDH) and glycerol dehydrogenase (GDH) of strain 10-1-A were expressed in Escherichia coli and the proteins were purified. meso-2,3-BD and (2R,3R)-2,3-BD were transformed from racemic acetoin by meso-BDH and GDH with NADH, respectively.

CONCLUSIONS

Compared with the reported GRAS 2,3-BD producers, B. licheniformis 10-1-A could thermophilically produce 2,3-BD with a high concentration, productivity and yield. Thus, the newly isolated GRAS strain 10-1-A might be a promising strain for industrial production of 2,3-BD. Two key enzymes for meso-2,3-BD and (2R,3R)-2,3-BD production were purified and further studied, and this might be helpful to understand the mechanism for 2,3-BD stereoisomers forming in B. licheniformis.

Genome sequences of two thermophilic Bacillus licheniformis strains, efficient producers of platform chemical 2,3-butanediol

Both Bacillus licheniformis strains 10-1-A and 5-2-D are efficient producers of 2,3-butanediol. Here we present 4.3-Mb and 4.2-Mb assemblies of their genomes. The key genes for the regulation and metabolism of 2,3-butanediol production were annotated, which may provide further insights into the molecular mechanism for the production of 2,3-butanediol with high yield and productivity.

Optimization and scale-up of 2,3-butanediol production by Bacillus amyloliquefaciens B10-127

The effects of culture conditions on 2,3-butanediol (2,3-BD) production and its possible scale-up have been studied. A newly isolated Bacillus amyloliquefaciens B10-127, belonged to GRAS microorganisms and showed a remarkable 2,3-BD producing potency, was used for this experiment. Corn steep liquor, soybean meal and ammonium citrate were found to be the key factors in the fermentation according to the results obtained from the Plackett-Burman experimental design. The optimal concentration range of the three factors was examined by the steepest ascent path, and their optimal concentration were further optimized via response surface methodological approach and determined to be 31.9, 22.0 and 5.58 g/l, respectively. The concentration of the obtained 2,3-BD increased significantly with optimized medium (62.7 g/l) when compared with unoptimized medium (45.7 g/l) and the 2,3-BD productivity was about 2.4-fold (The fermentation time was shorten from 72 to 42 h). To observe scale-up effects, batch fermentation was carried out at various working volumes. At a working volume of 20.0 l, the final 2,3-BD concentration and yield were 61.4 and 0.38 g/g at 36 h with a 2,3-BD productivity of 1.71 g/l h. This result shows similar amount of 2,3-BD obtained in lab-scale fermentation, and it is possible to scale up to larger fermentors without major problems.

Microbial 2,3-butanediol production: a state-of-the-art review

2,3-butanediol is a promising bulk chemical due to its extensive industry applications. The state-of-the-art nature of microbial 2,3-butanediol production is reviewed in this paper. Various strategies for efficient and economical microbial 2,3-butanediol production, including strain improvement, substrate alternation, and process development, are reviewed and compared with regard to their pros and cons. This review also summarizes value added derivatives of biologically produced 2,3-butanediol and different strategies for downstream processing. The future prospects of microbial 2,3-butanediol production are discussed in light of the current progress, challenges, and trends in this field. Guidelines for future studies are also proposed.

Effects of temperature, inoculum size and starch hydrolyzate concentration on butanediol production by Bacillus licheniformis

An optimization study has been performed on 2,3-butanediol production by Bacillus licheniformis NCIMB 8059 from different carbon sources (glucose, sucrose and cornstarch hydrolyzate), alternately varying temperature (34<T<40 degrees C), inoculum size (0.5<X(0)<10 gl(-1)), and starting substrate concentration (20<S(0)<70 gl(-1)). The results of average volumetric productivity obtained from tests at variable temperature have been worked out according to Arrhenius to estimate the thermodynamic parameters of both 2,3-butanediol formation (Deltah(*)=69.5 kJ mol(-1); Deltas(*)=-0.12 kJ mol(-1)K(-1)) and thermal inactivation equilibrium (Deltah( composite function )(D)=179 kJ mol(-1); Deltas( composite function )(D)=0.73 kJ mol(-1)K(-1)). The highest butanediol yield on starting glucose (Y=0.87 mol x mol(-1)) and average diol plus acetoin productivity (nu(av)=0.58 gl(-1)h(-1)) were obtained on cornstarch hydrolyzate at T=37 degrees C, pH 6.0, X(0)=10 gl(-1); S(0)=30 gl(-1) which suggests some stimulation in this raw material of the fermentative metabolism of B. licheniformis. Therefore, cornstarch hydrolyzate can be proposed as an alternative carbon source for industrial production of 2,3-butanediol with no need for growth factor addition.