Isolation and characterization of a newly identified Clostridium butyricum strain SCUT343-4 for 1,3-propanediol production

A novel 1,3-propanediol (1,3-PDO) producing strain was isolated and identified as Clostridium butyricum with respect to its morphological and physiological characteristics, as well as 16S rDNA. The results of substrates test and stress tolerance indicated that C. butyricum SCUT343-4 could produce 1,3-PDO efficiently from glycerol. The optimal fermentation conditions were determined to be 5 g/L yeast extract at 37 °C and pH 6.5. To fully evaluate its 1,3-PDO production capacity, different cultivation strategies have been implemented. The highest 1,3-PDO concentration obtained for batch and fed-batch fermentation were 51.64 and 61.30 g/L, respectively. Immobilized cell fermentation in fibrous-bed bioreactor was also performed, and the concentration of 1,3-PDO further increased to 86 g/L with a yield of 0.52 g/g. In addition, the 1,3-PDO productivity reached 4.20 g/L h, which is the highest level reported for C. butyricum, demonstrating the potential of C. butyricum SCUT343-4 for 1,3-PDO production from glycerol.

Production of n-butanol from cassava bagasse hydrolysate by engineered Clostridium tyrobutyricum overexpressing adhE2: Kinetics and cost analysis

The production of biofuels such as butanol is usually limited by the availability of inexpensive raw materials and high substrate cost. Using food crops as feedstock in the biorefinery industry has been criticized for its competition with food supply, causing food shortage and increased food prices. In this study, cassava bagasse as an abundant, renewable, and inexpensive byproduct from the cassava starch industry was used for n-butanol production. Cassava bagasse hydrolysate containing mainly glucose was obtained after treatments with dilute acid and enzymes (glucoamylases and cellulases) and then supplemented with corn steep liquor for use as substrate in repeated-batch fermentation with engineered Clostridium tyrobutyricum CtΔack-adhE2 in a fibrous-bed bioreactor. Stable butanol production with high titer (>15.0 g/L), yield (>0.30 g/g), and productivity (~0.3 g/L∙h) was achieved, demonstrating the feasibility of an economically competitive process for n-butanol production from cassava bagasse for industrial application.

n-Butanol production from lignocellulosic biomass hydrolysates without detoxification by Clostridium tyrobutyricum Δack-adhE2 in a fibrous-bed bioreactor

Acetone-butanol-ethanol fermentation suffers from high substrate cost and low butanol titer and yield. In this study, engineered Clostridium tyrobutyricum CtΔack-adhE2 immobilized in a fibrous-bed bioreactor was used for butanol production from glucose and xylose present in the hydrolysates of low-cost lignocellulosic biomass including corn fiber, cotton stalk, soybean hull, and sugarcane bagasse. The biomass hydrolysates obtained after acid pretreatment and enzymatic hydrolysis were supplemented with corn steep liquor and used in repeated-batch fermentations. Butanol production with high titer (∼15 g/L), yield (∼0.3 g/g), and productivity (∼0.3 g/L∙h) was obtained from cotton stalk, soybean hull, and sugarcane bagasse hydrolysates, while corn fiber hydrolysate with higher inhibitor contents gave somewhat inferior results. The fermentation process was stable for long-term operation without any noticeable degeneration, demonstrating its potential for industrial application. A techno-economic analysis showed that n-butanol could be produced from lignocellulosic biomass using this novel fermentation process at ∼$2.5/gal for biofuel application.

Production of butyric acid from acid hydrolysate of corn husk in fermentation by Clostridium tyrobutyricum: kinetics and process economic analysis

BACKGROUND

Butyric acid is an important chemical currently produced from petrochemical feedstocks. Its production from renewable, low-cost biomass in fermentation has attracted large attention in recent years. In this study, the feasibility of corn husk, an abundant agricultural residue, for butyric acid production by using Clostridium tyrobutyricum immobilized in a fibrous bed bioreactor (FBB) was evaluated.

RESULTS

Hydrolysis of corn husk (10% solid loading) with 0.4 M H₂SO₄ at 110 °C for 6 h resulted in a hydrolysate containing ~ 50 g/L total reducing sugars (glucose:xylose = 1.3:1.0). The hydrolysate was used for butyric acid fermentation by C. tyrobutyricum in a FBB, which gave 42.6 and 53.0% higher butyric acid production from glucose and xylose, respectively, compared to free-cell fermentations. Fermentation with glucose and xylose mixture (1:1) produced 50.37 ± 0.04 g L^-1 butyric acid with a yield of 0.38 ± 0.02 g g^-1 and productivity of 0.34 ± 0.03 g L^-1 h^-1. Batch fermentation with corn husk hydrolysate produced 21.80 g L^-1 butyric acid with a yield of 0.39 g g^-1, comparable to those from glucose. Repeated-batch fermentations consistently produced 20.75 ± 0.65 g L^-1 butyric acid with an average yield of 0.39 ± 0.02 g g^-1 in three consecutive batches. An extractive fermentation process can be used to produce, separate, and concentrate butyric acid to > 30% (w/v) sodium butyrate at an economically attractive cost for application as an animal feed supplement.

CONCLUSION

A high concentration of total reducing sugars at ~ 50% (w/w) yield was obtained from corn husk after acid hydrolysis. Stable butyric acid production from corn husk hydrolysate was achieved in repeated-batch fermentation with C. tyrobutyricum immobilized in a FBB, demonstrating that corn husk can be used as an economical substrate for butyric acid production.

Moderate alkali-thermophilic ethanologenesis by locally isolated Bacillus licheniformis from Pakistan employing sugarcane bagasse: a comparative aspect of aseptic and non-aseptic fermentations

BACKGROUND

Biofuels obtained from first-generation (1G) sugars-starch streams have been proven unsustainable as their constant consumption is not only significantly costly for commercial scale production systems, but it could potentially lead to problems associated with extortionate food items for human usage. In this regard, biofuels' production in alkali-thermophilic environs from second-generation (2G) bio-waste would not only be markedly feasible, but these extreme conditions might be able to sustain aseptic fermentations without spending much for sterilization.

RESULTS

Present investigation deals with the valuation of ethanologenic potential of locally isolated moderate alkali-thermophilic fermentative bacterium, Bacillus licheniformis KU886221 employing sugarcane cane bagasse (SCB) as substrate. A standard 2-factor central composite response surface design was used to estimate the optimized cellulolytic and hemicellulolytic enzymatic hydrolysis of SCB into maximum fermentable sugars. After elucidation of optimized levels of fermentation factors affecting ethanol fermentation using Taguchi OA L27 (3^13) experimental design, free cell batch culture was carried out in bench-scale stirred-tank bioreactor for ethanol fermentation. Succeeding fermentation modifications included subsequent substrate addition, immobilized cells fibrous-bed bioreactor (FBB) incorporation to the basic setup, and performance of in situ gas stripping for attaining improved ethanol yield. Highest ethanol yield of 1.1406 mol ethanol/mol of equivalent sugars consumed was obtained when gas stripping was performed during fed-batch fermentation involving FBB under aseptic conditions. Despite the fact that under non-aseptic conditions, 30.5% lesser ethanol was formed, still, reduced yield might be considered influential as it saved the cost of sterilization for ethanol production.

CONCLUSION

Effectual utilization of low-priced abundantly available lignocellulosic waste sugarcane bagasse under non-aseptic moderate alkali-thermophilic fermentation conditions as directed in this study has appeared very promising for large-scale cost-effective bioethanol generation processes.

Enhanced butanol production by coculture of Clostridium beijerinckii and Clostridium tyrobutyricum

Cocultures of Clostridium beijerinckii and Clostridium tyrobutyricum in free-cell and immobilized-cell fermentation modes were investigated as a means of enhancing butanol production. The immobilized fermentation was performed in a fibrous-bed bioreactor (FBB). The results demonstrated that two-strain coculture significantly enhanced butanol production, yield and volumetric productivity compared with those in pure culture with or without butyric acid. Further, continuous immobilized-cell cocultures in two FBBs using glucose, cassava starch, or cane molasses were conducted at a dilution rate of 0.144 h(-1). The butanol production (6.66 g/L), yield (0.18 g/g), and productivity (0.96 g/L/h) were obtained with cassava starch as the substrate. Meanwhile, the acetone-butanol-ethanol (ABE) yield (0.36 g/g) was the highest among all processes investigated, suggesting that this continuous coculture mode may be suitable for industrial ABE production with no need for repeated sterilization and inoculation.