Improved 1,3-propanediol production with hemicellulosic hydrolysates (corn straw) as cosubstrate: Impact of degradation products on Klebsiella pneumoniae growth and 1,3-propanediol fermentation

Homoethanol Production from Glycerol and Gluconate Using Recombinant Klebsiella oxytoca Strains

Gluconic acid, an oxidized cellulose degradation product, could be produced from cellulosic biomass. Glycerol is an inexpensive and renewable resource for fuels and chemicals production and is available as a byproduct of biodiesel production. Gluconate is a more oxidized substrate than glucose, whereas glycerol is a more reduced substrate than glucose. Although the production of homoethanol from glucose can be achieved, the conversion of gluconate to ethanol is accompanied by the production of oxidized byproduct such as acetate, and reduced byproducts such as 1,3-propanediol are produced, along with ethanol, when glycerol is used as the carbon source. When gluconate and glycerol are used as the sole carbon source by Klebsiella oxytoca BW21, the ethanol yield is about 62 to 64%. Coutilization of both gluconate and glycerol in batch fermentation increased the yield of ethanol to about 78.7% and decreased by-product accumulation (such as acetate and 1,3-propanediol) substantially. Decreasing by-product formation by deleting the pta, frd, ldh, pflA, and pduC genes in strain BW21 increased the ethanol yield to 89.3% in the batch fermentation of a glycerol-gluconate mixture. These deletions produced the strain K. oxytoca WT26. However, the utilization rate of glycerol was significantly slower than that of gluconate in batch fermentation. In addition, substantial amounts of glycerol remain unutilized after gluconate was depleted in batch fermentation. Continuous fed-batch fermentation was used to solve the utilization rate mismatch problem for gluconate and glycerol. An ethanol yield of 97.2% was achieved in continuous fed-batch fermentation of these two substrates, and glycerol was completely used at the end of the fermentation.IMPORTANCE Gluconate is a biomass-derived degradation product, and glycerol can be obtained as a biodiesel byproduct. Compared to glucose, using them as the sole substrate is accompanied by the production of by-products. Our study shows that through pathway engineering and adoption of a fed-batch culture system, high-yield homoethanol production that usually can be achieved by using glucose as the substrate is achievable using gluconate and glycerol as cosubstrates. The same strategy is expected to be able to achieve homofermentative production of other products, such as lactate and 2,3-butanediol, which can be typically achieved using glucose as the substrate and inexpensive biodiesel-derived glycerol and biomass-derived gluconate as the cosubstrates.

Xylan supplement improves 1,3-propanediol fermentation by Clostridium butyricum

Lignocellulosic biomass as co-substrate enhances the 1,3-propanediol (1,3-PD) production of anaerobic fermenters by increasing their conversion yield from glycerol. To improve 1,3-propanediol (1,3-PD) production by this efficient approach, Clostridium butyricum I5-42 was supplemented with lignocellulosic biomasses (starch free fiber (CPF) from cassava pulp and xylan) as co-substrates. The 1,3-PD production and growth of C. butyricum were considerably higher in glycerol plus CPF and xylan than in glycerol alone, whereas another major polysaccharide (cellulose co-substrate) failed to improve the 1,3-PD production. C. butyricum I5-42 showed no degradation ability on cellulose powder, and only weak activity and slight growth on xylan. However CPF supplemented with xylan strongly enhanced the transcription levels of the major enzymes of 1,3-PD production (glycerol dehydratase, 1,3-propanediol dehydrogenase, and glycerol dehydrogenase). The intracellular redox reactions maintained equal balance in the supplemented media, suggesting that CPF plus xylan promotes 1,3-PD production in the reductive pathway. This promotion is probably mediated by NADH, which is effectively regenerated by small amounts of released oligosaccharides and subsequent activation of the glycerol oxidative pathway. Both supplements also improved the 1,3-PD production at high glycerol concentration. Therefore, supplementation with lignocellulolytic polysaccharides such as xylan can improve the production and productivity of 1,3-PD from glycerol in C. butyricum. Direct supplementation of CPF with xylan in 1,3-PD production has not been previously reported.

Multi-modular engineering of 1,3-propanediol biosynthesis system in Klebsiella pneumoniae from co-substrate

1,3-Propanediol (1,3-PDO) is a monomer for the synthesis of various polyesters. It is widely used in industries including cosmetics, solvents, and lubricants. Here, the multi-modular engineering was used to improve the concentration and tolerance of 1,3-PDO in Klebsiella pneumoniae. Firstly, the concentration of 1,3-PDO was increased by 25 %, while the concentrations of by-products were reduced considerably through one-step evolution which focused on the glycerol pathway. In addition, the 1,3-PDO tolerance was improved to 150 g L^-1. Secondly, co-substrate transport system was regulated, and the 1,3-PDO concentration, yield, and productivity of the mutant were improved to 76.4 g L^-1, 0.53 mol mol^-1, and 2.55 g L^-1 h^-1, respectively. Finally, NADH regeneration was introduced and the recombinant strain was successfully achieved with a high productivity of 2.69 g L^-1 h^-1. The concentration and yield of 1,3-PDO were also improved to 86 g L^-1 and 0.59 mol mol^-1. This strategy described here provides an approach of achieving a superior strain which is able to produce 1,3-PDO with high productivity and yield.

Biological valorization of pure and crude glycerol into 1,3-propanediol using a novel isolate Lactobacillus brevis N1E9.3.3

The aim of the study was to evaluate a novel onsite enrichment approach to isolate a crude glycerol utilizing facultative anaerobic bacteria. An onsite enrichment in natural conditions resulted an isolate, Lactobacillus brevis N1E9.3.3, that can utilize glycerol and produce 1,3-propanediol with a yield of 0.89g1,3-PDO/gGlycerol and productivity of 0.78g1,3-PDO/l/h at pH-8.5 under anaerobic conditions. Batch fermentation experiments with glycerol-glucose co-fermentation strategy was carried out to evaluate the production of 1,3-propanediol and other byproducts. The effect of other carbon sources as co-substrate was also evaluated. At the optimized condition, 18.6g/l 1,3-propanediol was monitored when biodiesel industry generated crude glycerol and 2.5% glucose were used as the substrate.

Co-utilization of glycerol and lignocellulosic hydrolysates enhances anaerobic 1,3-propanediol production by Clostridium diolis

Anaerobic fermentation using lignocellulosic hydrolysates as co-substrates is an economically attractive method to enhance 1,3-propanediol (1,3-PD) production by increasing the conversion yield from glycerol. Lignocellulosic hydrolysates contain the mixed sugars that are primarily glucose, xylose, and arabinose. Therefore, these three individual sugars were used, separately, as co-substrates with glycerol, in 1,3-PD production by a Clostridium diolis strain DSM 15410, resulting in an 18%–28% increase in the 1,3-PD yield. Co-fermentation of the mixed sugars and glycerol obtained a higher intracellular NADH/NAD⁺ ratio and increased the 1,3-PD yield by 22% relative to fermentation of glycerol alone. Thereafter, two kinds of lignocellulosic hydrolysates, corn stover hydrolysate and corncob molasses, were individually co-fermented with glycerol. The maximum 1,3-PD yield from glycerol reached 0.85 mol/mol. Fed-batch co-fermentation was also performed, improving the 1,3-PD yield (from 0.62 mol/mol to 0.82 mol/mol). These results demonstrate that the co-fermentation strategy is an efficient and economical way to produce 1,3-PD from glycerol.

1,3-Propanediol production from glycerol with a novel biocatalyst Shimwellia blattae ATCC 33430: Operational conditions and kinetics in batch cultivations

Shimwellia blattae ATCC 33430 as biocatalyst in the conversion of 1,3-propanediol from glycerol is herein evaluated. Several operational conditions in batch cultivations, employing pure and raw glycerol as sole carbon source, were studied. Temperature was studied at shaken bottle scale, while pH control strategy, together with the influence of raw glycerol and its impurities during fermentation were studied employing a 2L STBR. Thereafter, fluid dynamic conditions were considered by changing the stirring speed and the gas supply (air or nitrogen) in the same scale-up experiments. The best results were obtained at a temperature of 37°C, an agitation rate of 200rpm, with free pH evolution from 6.9 and subsequent control at 6.5 and no gas supply during the fermentation, employing an initial concentration of 30g/L of raw glycerol. Under these conditions, the biocatalyst is competitive, leading to results in line with other previous works in the literature in batch conditions, reaching a final concentration of 1,3-propanediol of 13.84g/L, with a yield of 0.45g/g and a productivity of 1.19g/(Lh) from raw glycerol.

Highly efficient rice straw utilization for poly-(γ-glutamic acid) production by Bacillus subtilis NX-2

Lignocellulosic biomass has been identified as an economic and environmental feedstock for future biotechnological production. Here, for the first time, poly-(γ-glutamic acid) (PGA) production by Bacillus subtilis NX-2 using rice straw is investigated. Based on two-stage hydrolysis and characteristic consumption of xylose and glucose by B. subtilis NX-2, a co-fermentation strategy was designed to better accumulate PGA in a 7.5L fermentor by two feeding methods. The maximum cumulative respective PGA production and PGA productivity were 73.0 ± 0.5 g L(-1) and 0.81 g L(-1) h(-1) by the continuous feeding method, with carbon source cost was saved by 84.2% and 42.5% compared with glucose and cane molasse, respectively. These results suggest that rice straw, a type of abundant, low-cost, non-food lignocellulosic feedstock, may be feasibly and efficiently utilized for industrial-scale production of PGA.

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.

Biorefinery development through utilization of biodiesel industry by-products as sole fermentation feedstock for 1,3-propanediol production

Rapeseed meal (RSM) hydrolysate was evaluated as substitute for commercial nutrient supplements in 1,3-propanediol (PDO) fermentation using the strain Clostridium butyricum VPI 1718. RSM was enzymatically converted into a generic fermentation feedstock, enriched in amino acids, peptides and various micro-nutrients, using crude enzyme consortia produced via solid state fermentation by a fungal strain of Aspergillus oryzae. Initial free amino nitrogen concentration influenced PDO production in batch cultures. RSM hydrolysates were compared with commercial nutrient supplements regarding PDO production in fed-batch cultures carried out in a bench-scale bioreactor. The utilization of RSM hydrolysates in repeated batch cultivation resulted in a PDO concentration of 65.5 g/L with an overall productivity of 1.15 g/L/h that was almost 2 times higher than the productivity achieved when yeast extract was used as nutrient supplement.

The production of 1,3-propanediol from mixtures of glycerol and glucose by a Klebsiella pneumoniae mutant deficient in carbon catabolite repression

In the present study, mutant strain of Klebsiella pneumoniae with deletion of the crr gene encoding EIIA(Glc) (a component of the glucose-specific phosphoenolpyruvate-dependent transferase system [PTS]) was prepared. This eliminated the ability of the strain to mediate carbon catabolite repression (CCR). Production of 1,3-propanediol (1,3-PD) from glycerol by the crr mutant strain was enhanced (compared to that of the parent) in the presence of glucose. Using molasses as a co-substrate of glycerol, the maximum yield of 1,3-PD was 60.4% greater (81.2g/l) than that obtained when glycerol was used alone, under optimum fermentation conditions.

Simultaneous production of 3-hydroxypropionic acid and 1,3-propanediol from glycerol by a recombinant strain of Klebsiella pneumoniae

In this study, an aldehyde dehydrogenase (ALDH) was over-expressed in Klebsiella pneumoniae for simultaneous production of 3-hydroxypropionic acid (3-HP) and 1,3-propanediol (1,3-PDO). Various genes encoding ALDH were cloned and expressed in K. pneumoniae, and expression of Escherichia colialdH resulted in the highest 3-HP titer in anaerobic cultures in shake flasks. Anaerobic fed-batch culture of this recombinant strain was further performed in a 5-L reactor. The 3-HP concentration and yield reached 24.4 g/L and 0.18 mol/mol glycerol, respectively, and at the same time 1,3-PDO achieved 49.3 g/L with a yield of 0.43 mol/mol in 24 h. The overall yield of 3-HP plus 1,3-PDO was 0.61 mol/mol. Over-expression of the E. coli AldH also reduced the yields of by-products except for lactate. This study demonstrated the possibility of simultaneous production of 3-HP and 1,3-PDO by K. pneumoniae under anaerobic conditions without supply of vitamin B12.

Impact of anaerobiosis strategy and bioreactor geometry on the biochemical response of Clostridium butyricum VPI 1718 during 1,3-propanediol fermentation

The impact of anaerobiosis strategy on 1,3-propanediol production during cultivation of Clostridium butyricum VPI 1718 in different size bioreactors was studied. In batch trials with N2 gas infusion, the fermentation was successfully accomplished, regardless of initial glycerol concentration imposed and bioreactor geometry. However, in the absence of N2 continual sparging, significant variations concerning the biochemical response of the strain were observed. Specifically, at 1-L bioreactor, the absence of N2 infusion at high initial glycerol concentration induced lactate dehydrogenase activity and thus lactic acid synthesis, probably due to partial blockage of phosphoroclastic reaction caused by insufficient self-generated anaerobiosis environment. During fed-batch cultivation with continual N2 sparging, the strain produced ∼71 g L(-1) of 1,3-propanediol, whereas under self-generated anaerobiosis, 1,3-propanediol pathway was evidently restricted, as only 30.5 g L(-1) of 1,3-propanediol were finally produced. Apparently, N2 infusion strategy paired with bioreactor geometry can alter the biochemical behavior of the particular strain.