Stoichiometric analysis and experimental investigation of glycerol–glucose co-fermentation in Klebsiella pneumoniae under microaerobic conditions

Production of 1,3-propanediol by Lactobacillus diolivorans from agro-industrial residues and cactus cladode acid hydrolyzate

This study evaluated the bioproduction of 1,3-propanediol by Lactobacillus diolivorans in the medium based on agro-industrial residues and vegetal biomass substituting the MRS medium components. It was performed on a set of acid treatments and batch fermentations assays with crude glycerol (TCG) from biodiesel production, corn steep liquor (CSL), and cactus cladode hydrolyzate (CCH). Firstly, it was carried out on batch fermentation with different pure glycerol concentrations in MRS medium which was carried out, and the best condition achieved 4.66 g/L and 0.61 g/g of 1,3-PDO production and yield, respectively. Then, the TCG was evaluated, and a discrete increase of 1,3-PDO was observed. The replacement of the MRS medium nutrients by CLS was assessed, at different concentrations, for bacteria growth, and 5% of CLS reproduced the same biomass formation compared to the bacteria growth in MRS medium. It was also added cactus cladode hydrolyzate as the only sugar source, which showed a 1,3-PDO production close to the medium with pure glucose. Finally, a B-complex vitamin was added to the batch fermentation medium composed of TCG, CLS, and CCH, replacing all the costly MRS components. In this medium, the production of 1,3-propanediol was 6.57 g/L with a yield of 0.75 g/g. It means an increment of 29% and 19%, respectively, compared to MRS medium. Therefore, the combination of treated crude glycerol, corn steep liquor, and cactus cladode hydrolyzate has excellent potential for 1,3-PDO production by L. diolivorans.

Co-fermentation of glycerol and glucose by a co-culture system of engineered Escherichia coli strains for 1,3-propanediol production without vitamin B12 supplementation

The necessity of costly co-enzyme B₁₂ for the activity of glycerol dehydratase (GDHt) is considered as a major bottleneck in sustainable bioproduction of 1,3-propanediol (1,3-PD) from glycerol. Here, an E. coil Rosetta-dhaB1-dhaB2 strain was constructed by overexpressing a B₁₂-independent GDHt (dhaB1) and its activating factor (dhaB2) from Clostridium butyricum. Subsequently, it was used in designing a co-culture with E. coli BL21-dhaT that overexpressed 1,3-PD oxidoreductase (dhaT), to produce 1,3-PD during co-fermentation of glycerol and glucose. The optimum initial ratio of BL21-dhaT to Rosetta-dhaB1-dhaB2 strains in the co-culture was 1.5. Compared to the fermentation of glycerol alone, co-fermentation approach provided 1.3-folds higher 1,3-PD. Finally, co-fermentation was done in a 10 L bioreactor that produced 41.65 g/L 1,3-PD, which corresponded to 0.69 g/L/h productivity and 0.67 mol/mol yield of 1,3-PD. Hence, the developed co-culture could produce 1,3-PD cost-effectively without requiring vitamin B₁₂.

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.

Exploring Dual-Substrate Cultivation Strategy of 1,3-Propanediol Production Using Klebsiella pneumoniae

1,3-Propanediol (1,3-PDO) has numerous industrial applications in the synthesis of the monomer of the widely used fiber polytrimethylene terephthalate. In this work, the production of 1,3-PDO by Klebsiella pneumoniae is increased by dual-substrate cultivation and fed-batch fermentation. Experimental results indicate that the production of 1,3-PDO can be elevated to 16.09 g/L using a dual substrate ratio (of glucose to crude glycerol) of 1/30 and to 20.73 g/L using an optimized dual-substrate ratio of 1/20. Ultimately, the optimal dual-substrate feeding for a 5 L scale fed-batch fermenter that maximizes 1,3-PDO production (29.69 g/L) is determined. This production yield is better than that reported in most related studies. Eventually, the molecular weight and chemical structure of 1,3-PDO were obtained by FAB-MS, ¹H-NMR, and ¹³C-NMR. Also, in demonstrating the effectiveness of the fermentation strategy in increasing the production and production yield of 1,3-PDO, experimental results indicate that the fermentation of 1,3-PDO is highly promising for commercialization.

Co-production of 1,3-Propanediol and 2,3-Butanediol from Waste Lard by Co-cultivation of Pseudomonas alcaligenes and Klebsiella pneumoniae

The platform chemicals 1,3-propanediol (1,3-PD) and 2,3-butanediol (2,3-BD) are important raw materials for polyesters and biofuels. However, the biosynthesis of the compounds relies on massive consumption of glucose or glycerol, leading to the uneconomical production in industrial scale. In this work, we developed a new method for co-production of 1,3-PD and 2,3-BD from waste lard to reduce the cost in carbon source supply. A waste lard utilizing Pseudomonas alcaligenes PA-3 and a 1,3-PD producing Klebsiella pneumoniae AA405 were co-cultivated by using waste lard as the sole carbon source. In a shake flask, 1.05 g/L 1,3-PD and 0.35 g/L 2,3-BD were produced from waste lard within 24 h. The addition of nitrogen source significantly increased the relative ratio of K. pneumoniae AA405 in the medium, which further favored to the higher titers of the two products. In bioreactor, the co-cultivation system produced 5.98 g/L 1,3-PD and 4.29 g/L 2,3-BD from 100 g/L waste lard within 72 h, and the conversion rate of 1,3-PD and 2,3-BD from waste lard were 62.95% and 0.75%, respectively. In all, this is the first work on 1,3-PD and 2,3-BD production from waste triglyceride, which will favor the utilization of low-cost carbon source in industrial production of chemicals.

1,3-Propanediol production by Klebsiella oxytoca NRRL-B199 from glycerol. Medium composition and operational conditions

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1,3-Propanediol is produced from glycerol using Klebsiella oxytoca NRRL-B199.

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The medium composition was optimized by an orthogonal experimental design.

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Scale-up form shaken bottles to STBR was studied.

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Operating conditions, agitation and temperature, were optimized.

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Under these conditions, 13.5 g/L of propanediol (selectivity = 86% with respect to glycerol) can be obtained.

Production of 1,3-propanediol from glycerol using Klebsiella oxytoca NRRL-B199 has been studied. Medium composition has been optimized by means of a statistical design based on the Taguchi method. Strong influences of glycerol and phosphate concentrations have been detected on biomass and product yields. Other factors, such as magnesium concentration and K:Na ratio, have shown a small influence on both responses, biomass and product concentrations. An optimized medium composition has been proposed, leading to a final 1,3-propanediol concentration of 12.4 g/L with a selectivity of 72% with respect to glycerol consumed at shaken bottle-scale. Once the medium composition had been optimized, the scale-up from shaken bottles to STBR was conducted. Several experiments in a 2 L STBR have been conducted in order to determine the best operating conditions concerning temperature and agitation.

Under the best operating conditions, i.e., a programmed variable stirring rate ranging from 50 to 100 rpm and a temperature of 37 °C, a final concentration of 13.5 g/L of 1,3-propanediol with a selectivity of 86% with respect to the glycerol consumed was obtained.

1,3-propanediol production with Citrobacter werkmanii DSM17579: effect of a dhaD knock-out

Background

1,3-propanediol (PDO) is a substantially industrial metabolite used in the polymer industry. Although several natural PDO production hosts exist, e.g. Klebsiella sp., Citrobacter sp. and Clostridium sp., the PDO yield on glycerol is insufficient for an economically viable bio-process. Enhancing this yield via strain improvement can be achieved by disconnecting the production and growth pathways. In the case of PDO formation, this approach results in a microorganism metabolizing glycerol strictly for PDO production, while catabolizing a co-substrate for growth and maintenance. We applied this strategy to improve the PDO production with Citrobacter werkmanii DSM17579.

Results

Genetic tools were developed and used to create Citrobacter werkmanii DSM17579 ∆dhaD in which dhaD, encoding for glycerol dehydrogenase, was deleted. Since this strain was unable to grow on glycerol anaerobically, both pathways were disconnected. The knock-out strain was perturbed with 13 different co-substrates for growth and maintenance. Glucose was the most promising, although a competition between NADH-consuming enzymes and 1,3-propanediol dehydrogenase emerged.

Conclusion

Due to the deletion of dhaD in Citrobacter werkmanii DSM17579, the PDO production and growth pathway were split. As a consequence, the PDO yield on glycerol was improved 1,5 times, strengthening the idea that Citrobacter werkmanii DSM17579 could become an industrially interesting host for PDO production.

Propionic acid production in glycerol/glucose co-fermentation by Propionibacterium freudenreichii subsp. shermanii

Propionibacterium freudenreichii subsp. shermanii can ferment glucose and glycerol to propionic acid with acetic and succinic acids as two by-products. Propionic acid production from glucose was relatively fast (0.19 g/Lh) but gave low product yield (~0.39 g/g) and selectivity (P/A: ~2.6; P/S: ~4.8). In contrast, glycerol with a more reduced state gave a high propionic acid yield (~0.65 g/g) and selectivity (P/A: ~31; P/S: ~11) but low productivity (0.11 g/L h). On the other hand, co-fermentation of glycerol and glucose at an appropriate mass ratio gave both a high yield (0.54-0.65 g/g) and productivity (0.18-0.23 g/L h) with high product selectivity (P/A: ~14; P/S: ~10). The carbon flux distributions in the co-fermentation as affected by the ratio of glycerol/glucose were investigated. Finally, co-fermentation with cassava bagasse hydrolysate and crude glycerol in a fibrous-bed bioreactor was demonstrated, providing an efficient way for economic production of bio-based propionic acid.

1,3-Propanediol production from crude glycerol from Jatropha biodiesel process

The present report describes production of 1,3-propanediol by Klebsiella pneumoniae ATCC 15380 from crude glycerol from jatropha biodiesel process. Optimization resulted in a yield of up to 56g/L of 1,3-propanediol. A conversion rate of 0.85mol 1,3-propanediol/mol of glycerol has been obtained. Downstream processing to isolate 1,3-propanediol from the fermentation broth resulted in 99.7% pure product with a recovery of 34%. The pure 1,3-propanediol was polymerized with terephthalic acid successfully to yield polytrimethylene terephthalate.

Glycerol/glucose co-fermentation: one more proficient process to produce propionic acid by Propionibacterium acidipropionici

Cosubstrates fermentation is such an effective strategy for increasing subject metabolic products that it could be available and studied in propionic acid production, using glycerol and glucose as carbon resources. The effects of glycerol, glucose, and their mixtures on the propionic acid production by Propionibacterium acidipropionici CGMCC1.2225 (ATCC4965) were studied, with the aim of improving the efficiency of propionic acid production. The propionic acid yield from substrate was improved from 0.475 and 0.303 g g⁻¹ with glycerol and glucose alone, respectively, to 0.572 g g⁻¹ with co-fermentation of a glycerol/glucose mixture of 4/1 (mol/mol). The maximal propionic acid and substrate conversion rate were 21.9 g l⁻¹ and 57.2% (w/w), respectively, both significantly higher than for a sole carbon source. Under optimized conditions of fed-batch fermentation, the maximal propionic acid yield and substrate conversion efficiency were 29.2 g l⁻¹ and 54.4% (w/w), respectively. These results showed that glycerol/glucose co-fermentation could serve as an excellent alternative to conventional propionic acid fermentation.