Effects of genetic modifications and fermentation conditions on 2,3-butanediol production by alkaliphilic Bacillus subtilis

Carrot Discard as a Promising Feedstock to Produce 2,3-Butanediol by Fermentation with P. polymyxa DSM 365

The valorization of fruit and vegetable residues (such as carrot discard) and their microbial conversion into 2,3-butanediol (BDO) can be considered as a very interesting way to reduce food waste and sustainably originate high value-added products. This work analyzes the valorization of carrot discard as feedstock for 2,3-butanediol (BDO) production by Paenibacillus polymyxa DSM 365. The influences of stirring and the presence of tryptone (nitrogen source) are studied. Furthermore, in order to evaluate the influence of the pre-culture medium (nitrogen source, nutrients, and pH) and the substrate, fermentation assays in simple and mixture semi-defined media (glucose, fructose, and/or galactose) were also carried out. As a result, 18.8 g/L BDO, with a BDO yield of 0.43 g/g (86% of its theoretical value), could be obtained from carrot discard enzymatic hydrolysate at 100 rpm, no tryptone, and pre-culture Häßler medium. No hydrothermal pre-treatment was necessary for BDO production from carrot discard, which increases the profitability of the process. Therefore, 18.8 g BDO, as well as 2.5 g ethanol and 2.1 g acetoin by-products, could be obtained from 100 g of carrot discard (dry matter).

Regulation of carbon flux and NADH/NAD+ supply to enhance 2,3-butanediol production in Enterobacter aerogenes

As a valuable platform chemical, 2,3-Butanediol (2,3-BDO) has a variety of industrial applications, and its microbial production is particularly attractive as an alternative to petroleum-based production. In this study, the regulation of intracellular carbon flux and NADH/NAD⁺ was used to increase the 2,3-BDO production of Enterobacter aerogenes. The genes encoding lactate dehydrogenase (ldh) and pyruvate formate lyase (pfl) were disrupted using the λ-Red recombination method and CRISPR-Cas9 to reduce the production of several byproducts and the consumption of NADH. Knockout of ldh or pfl increased intracellular NADH/NAD⁺ by 111 % and 113 %, respectively. Moreover, two important genes in the 2,3-BDO biosynthesis pathway, acetolactate synthase (budB) and acetoin reductase (budC), were overexpressed in E. aerogenes to further amply the metabolic flux toward 2,3-BDO production. And the overexpression of budB or budC increased intracellular NADH/NAD⁺ by 46 % and 57 %, respectively. In shake-flask cultivation with sucrose as carbon source, the 2,3-BDO titer of the IAM1183-LPBC was 3.55 times that of the wild type. In the 5-L fermenter, the maximal 2,3-BDO production produced by the IAM1183-LPBC was 2.88 times that of the original strain. This work offers new ideas for promoting the biosynthesis of 2,3-BDO for industrial applications.

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.

Metabolic regulation and optimization of oxygen supply enhance the 2,3-butanediol yield of the novel Klebsiella sp. isolate FSoil 024

BACKGROUND

Biogenic 2,3-butanediol (2,3-BDO) is a high-value-added compound that can be used as a liquid fuel and a platform chemical. Bioproduction of 2,3-BDO is an environmentally friendly choice.

METHOD AND RESULTS

Three recombinant derivatives of the novel Klebsiella sp. isolate FSoil 024 (WT) were constructed via different strategies including deletion of lactate dehydrogenase by λ-Red homologous recombination technology, overexpression of the small-noncoding RNA RyhB and a combination of both. The 2,3-BDO productivity of the mutants increased by 61.3-79%, and WT-Δldh/ryhB displayed the highest 2,3-BDO yield of 42.36 mM after 24 h of shake-flask fermentation. Glucose was shown as the best carbon source for 2,3-BDO production by WT-Δldh/ryhB. In addition, higher oxygenation was favorable for ideal product synthesis. The maximal 2,3-BDO yield of WT and WT-Δldh/ryhB were increased by 23.3 and 52.5% respectively compared to the control group in the presence of 70% oxygen (V:V' = O₂ :(O₂ +N₂ )).

CONCLUSION AND IMPLICATIONS

According to the present study, deletion of lactate dehydrogenase, RyhB overexpression and manipulation of oxygen supply showed great impacts on cell growth, 2,3-BDO productivity and cellular metabolism of the novel isolated strain Klebsiella sp. FSoil 024. This work would also provide insights for promoting 2,3-BDO biosynthesis for industrial applications. This article is protected by copyright. All rights reserved.

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.

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.

Recent Advances in the Microbial Synthesis of Hemoglobin

Hemoglobin is a cofactor-containing protein with heme that plays important roles in transporting and storing oxygen. Hemoglobins have been widely applied as acellular oxygen carriers, bioavailable iron-supplying agents, and food-grade coloring and flavoring agents. To meet increasing demands and overcome the drawbacks of chemical extraction, the biosynthesis of hemoglobin has become an attractive alternative. Several hemoglobins have recently been synthesized by various microorganisms through metabolic engineering and synthetic biology. In this review, we summarize the novel strategies that have been used to biosynthesize hemoglobin. These strategies can also serve as references for producing other heme-binding proteins.

Simultaneous production of poly-γ-glutamic acid and 2,3-butanediol by a newly isolated Bacillus subtilis CS13

Bacillus subtilis naturally produces large amounts of 2,3-butanediol (2,3-BD) as a main by-product during poly-γ-glutamic acid (γ-PGA) production. 2,3-BD is a promising platform chemical in various industries, and co-production of the two chemicals has great economic benefits. Co-production of γ-PGA and 2,3-BD by a newly isolated B. subtilis CS13 was investigated here. The fermentation medium and culture parameters of the process were optimized using statistical methods. It was observed that sucrose, L-glutamic acid, ammonium citrate, and MgSO₄·7H₂O were favorable for γ-PGA and 2,3-BD co-production at culture pH of 6.5 and 37 °C. An optimal medium composed of 119.8 g/L sucrose, 48.8 g/L L-glutamic acid, 21.1 g/L ammonium citrate, and 3.2 g/L MgSO₄·7H₂O was obtained by response surface methodology (RSM). The results show that the titers of γ-PGA and 2,3-BD reached 27.8 ± 0.9 g/L at 24 h and 57.1 ± 1.3 g/L at 84 h with the optimized medium, respectively. γ-PGA and 2,3-BD production by B. subtilis CS13 was significantly enhanced in fed-batch fermentations. γ-PGA (36.5 ± 1.1 g/L, productivity of 1.22 ± 0.04 g/L/h) and 2,3-BD concentrations (119.6 ± 2.8 g/L, productivity of 2.49 ± 0.66 g/L/h) were obtained in the optimized medium with feeding sucrose. The co-production of 2,3-BD and γ-PGA provides a new perspective for industrial production of γ-PGA and 2,3-BD. Key points • A strategy for co-production of γ-PGA and 2,3-BD was developed. • The culture parameters for the co-production of γ-PGA and 2,3-BD were studied. • RSM was used to optimize the medium for γ-PGA and 2,3-BD co-production. • 36.5 g/L γ-PGA and 119.6 g/L 2,3-BD were obtained from the optimum medium in fed-batch fermentation.

Improvement of menaquinone-7 production by Bacillus subtilis natto in a novel residue-free medium by increasing the redox potential

Bacillus subtilis natto is a GRAS bacterium. Nattokinase, with fibrinolytic and antithrombotic activities, is one of the major products of this organism. It is being gradually recognized that B. subtilis natto can also be used as a biosynthetic strain for vitamin K2, which has phenomenal benefits, such as effects in the prevention of cardiovascular diseases and osteoporosis along with antitumor effects. Knocking out of the aprN gene by homologous recombination could improve the redox potential and slightly increase the concentration of MK-7. By detecting the change in redox potential during the growth of B. subtilis natto, a good oxygen supply and state of the cell membrane were found to be beneficial to vitamin K2 synthesis. A two-step RSM was used to optimize the operation parameters and substrate concentration in the new residue-free fermentation culture. The optimal conditions for the residue-free medium and control were determined. The optimum concentrations of soybean flour, corn flour, and peptone were 78.9, 72.4, and 24.8 g/L, respectively. The optimum rotational speed and volume of the culture medium using a shaking flask were 117 rpm and 10%, respectively. The state and composition of the cell membranes were more stable when engineered bacteria were cultured in this residue-free fermentation medium. Finally, the concentration of MK-7 increased by 37% to 18.9 mg/L, and the fermentation time was shortened by 24 h.