Butanol production from acid hydrolyzed corn fiber with Clostridium beijerinckii mutant

Saccharification of lignocellulosic biomass using an enzymatic cocktail of fungal origin and successive production of butanol by Clostridium acetobutylicum

A multistep approach was undertaken for biobutanol production targeting valorization of agricultural waste. Optimum production of lignocellulolytic enzymes [CMCase (3822.93U/mg), FPase (3640.93U/mg), β-glucosidase (3873.92U/mg), xylanase (3460.24U/mg), pectinase (3359.57U/mg), α-amylase (4136.54U/mg), and laccase (3863.16U/mg)] was accomplished through solid-substrate fermentation of pretreated mixed substrates (wheat bran, sugarcane bagasse and orange peel) by Aspergillus niger SKN1 and Trametes hirsuta SKH1. Partially purified enzyme cocktail was employed for saccharification of the said substrate mixture into fermentable sugar (69.23 g/L, product yield of 24% w/w). The recovered sugar with vegetable extract supplements was found as robust fermentable medium that supported 16.51 g/L biobutanol production by Clostridium acetobutylicum ATCC824. The sequential bioprocessing of low-priced substrates and exploitation of vegetable extract as growth factor for microbial butanol production will open a new vista in biofuel research.

Reassessment of the role of CaCO3 in n-butanol production from pretreated lignocellulosic biomass by Clostridium acetobutylicum

In this study, the role of CaCO₃ in n-butanol production was further investigated using corn straw hydrolysate (CSH) media by Clostridium acetobutylicum CICC 8016. CaCO₃ addition stimulated sugars utilization and butanol production. Further study showed that calcium salts addition to CSH media led to the increase in Ca²⁺ concentration both intracellularly and extracellularly. Interestingly, without calcium salts addition, intracellular Ca²⁺ concentration in the synthetic P2 medium was much higher than that in the CSH medium despite the lower extracellular Ca²⁺ concentrations in the P2 medium. These results indicated that without additional calcium salts, Ca²⁺ uptake by C. acetobutylicum CICC 8016 in the CSH medium may be inhibited by non-sugar biomass degradation compounds, such as furans, phenolics and organic acids. Comparative proteomics analysis results showed that most enzymes involved in glycolysis, redox balance and amino acids metabolism were up-regulated with CaCO₃ addition. This study provides further insights into the role of CaCO₃ in n-butanol production using real biomass hydrolysate.

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.

CRISPR/Cas9-Based Efficient Genome Editing in Clostridium ljungdahlii, an Autotrophic Gas-Fermenting Bacterium

Acetogenic bacteria have the potential to convert single carbon gases (CO and CO2) into a range of bulk chemicals and fuels. Realization of their full potential is being impeded by the absence of effective genetic tools for high throughput genome modification. Here we report the development of a highly efficient CRISPR/Cas9 system for rapid genome editing of Clostridium ljungdahlii, a paradigm for the commercial production of ethanol from synthesis gas. Following the experimental selection of two promoters (Pthl and ParaE) for expression of cas9 and the requisite single guide RNA (sgRNA), the efficiency of system was tested by making precise deletions of four genes, pta, adhE1, ctf and pyrE. Deletion efficiencies were 100%, >75%, 100% and >50%, respectively. The system overcomes the deficiencies of currently available tools (more rapid, no added antibiotic resistance gene, scarless and minimal polar effects) and will find utility in other acetogens, including the pathogen Clostridium difficile.

Effect of dilute alkaline pretreatment on the conversion of different parts of corn stalk to fermentable sugars and its application in acetone-butanol-ethanol fermentation

To investigate the effect of dilute alkaline pretreatment on different parts of biomass, corn stalk was separated into flower, leaf, cob, husk and stem, which were treated by NaOH in range of temperature and chemical loading. The NaOH-pretreated solid was then enzymatic hydrolysis and used as the substrate for batch acetone-butanol-ethanol (ABE) fermentation. The results demonstrated the five parts of corn stalk could be used as potential feedstock separately, with vivid performances in solvents production. Under the optimized conditions towards high product titer, 7.5g/L, 7.6g/L, 9.4g/L, 7g/L and 7.6g/L of butanol was obtained in the fermentation broth of flower, leaf, cob, husk and stem hydrolysate, respectively. Under the optimized conditions towards high product yield, 143.7g/kg, 126.3g/kg, 169.1g/kg, 107.7g/kg and 116.4g/kg of ABE solvent were generated, respectively.

Enhanced isopropanol and n-butanol production by supplying exogenous acetic acid via co-culturing two clostridium strains from cassava bagasse hydrolysate

The focus of this study was to produce isopropanol and butanol (IB) from dilute sulfuric acid treated cassava bagasse hydrolysate (SACBH), and improve IB production by co-culturing Clostridium beijerinckii (C. beijerinckii) with Clostridium tyrobutyricum (C. tyrobutyricum) in an immobilized-cell fermentation system. Concentrated SACBH could be converted to solvents efficiently by immobilized pure culture of C. beijerinckii. Considerable solvent concentrations of 6.19 g/L isopropanol and 12.32 g/L butanol were obtained from batch fermentation, and the total solvent yield and volumetric productivity were 0.42 g/g and 0.30 g/L/h, respectively. Furthermore, the concentrations of isopropanol and butanol increased to 7.63 and 13.26 g/L, respectively, under the immobilized co-culture conditions when concentrated SACBH was used as the carbon source. The concentrations of isopropanol and butanol from the immobilized co-culture fermentation were, respectively, 42.62 and 25.45 % higher than the production resulting from pure culture fermentation. The total solvent yield and volumetric productivity increased to 0.51 g/g and 0.44 g/L/h when co-culture conditions were utilized. Our results indicated that SACBH could be used as an economically favorable carbon source or substrate for IB production using immobilized fermentation. Additionally, IB production could be significantly improved by co-culture immobilization, which provides extracellular acetic acid to C. beijerinckii from C. tyrobutyricum. This study provided a technically feasible and cost-efficient way for IB production using cassava bagasse, which may be suitable for industrial solvent production.

Combination of RNA sequencing and metabolite data to elucidate improved toxic compound tolerance and butanol fermentation of Clostridium acetobutylicum from wheat straw hydrolysate by supplying sodium sulfide

Sodium sulfide (SS) was added to the non-detoxified wheat straw hydrolysate for ABE fermentation by Clostridium acetobutylicum CICC8012. Biochemical measurements demonstrated that supplementation with SS promoted earlier and enhanced conversion of acid to ABE and led to a 27.48% improvement in sugar consumption, a 20.48% improvement in the sugar-based ABE yield, a 47.63% improvement in the butanol titer, and a 53.50% improvement in the ABE concentration. The response of C. acetobutylicum CICC8012 at the mRNA level was examined by a transcriptional analysis performed with RNA sequencing. The expression of genes involved in the membrane transport of carbohydrates, glycolysis, and ABE formation increased following SS-supplemented fermentation, whereas the expression of genes encoding enzymes involved in acid formation decreased, which indicates that supplemental SS affected the central fermentative pathway, down-regulated the metabolic flux toward the acid formation branches, and up-regulated the metabolic flux toward the ABE formation branches.

Mutagenesis breeding of high echinocandin B producing strain and further titer improvement with culture medium optimization

A combination of microbial strain improvement and statistical optimization is investigated to maximize echinocandin B (ECB) production from Aspergillus nidulans ZJB-0817. A classical sequential mutagenesis was studied first by using physical (ultraviolet irradiation at 254 nm) and chemical mutagens (lithium chloride and sodium nitrite). Mutant strain ULN-59 exhibited 2.1-fold increase in ECB production to 1583.1 ± 40.9 mg/L when compared with the parent strain (750.8 ± 32.0 mg/L). This is the first report where mutagenesis is applied in Aspergillus to improve ECB production. Further, fractional factorial design and central composite design were adopted to optimize the culture medium for increasing ECB production by the mutant ULN-59. Results indicated that four culture media including peptone, K2HPO4, mannitol and L-ornithine had significant effects on ECB production. The optimized medium provided another 1.4-fold increase in final ECB concentration to 2285.6 ± 35.6 mg/L compared to the original medium. The results of this study indicated the combined application of a classical mutation and medium optimization can improve effectively ECB production from A. nidulans and could be a promising tool to improve other secondary metabolites production by fungal strains.

Acetone-butanol-ethanol fermentation of corn stover by Clostridium species: present status and future perspectives

Sustainable vehicle fuel is indispensable in future due to worldwide depletion of fossil fuel reserve, oil price fluctuation and environmental degradation. Microbial production of butanol from renewable biomass could be one of the possible options. Renewable biomass such as corn stover has no food deficiency issues and is also cheaper in most of the agricultural based countries. Thus it can effectively solve the existing issue of substrate cost. In the last 30 years, a few of Clostridium strains have been successfully implemented for biobutanol fermentation. However, the commercial production is hindered due to their poor tolerance to butanol and inhibitors. Metabolic engineering of Clostridia strains is essential to solve above problems and ultimately enhance the solvent production. An effective and efficient pretreatment of raw material as well as optimization of fermentation condition could be another option. Furthermore, biological approaches may be useful to optimize both the host and pathways to maximize butanol production. In this context, this paper reviews the existing Clostridium strains and their ability to produce butanol particularly from corn stover. This study also highlights possible fermentation pathways and biological approaches that may be useful to optimize fermentation pathways. Moreover, challenges and future perspectives are also discussed.

Butanol fermentation

This review provides an overview on bacterial butanol production and recent developments concerning strain improvement, newly built butanol production plants, and the importance of alternative substrates, especially lignocellulosic hydrolysates. The butanol fermentation using solventogenic clostridial strains, particularly Clostridium acetobutylicum, is a very old industrial process (acetone-butanol-ethanol-ABE fermentation). The genome of this organism has been sequenced and analysed, leading to important improvements in rational strain construction. As the traditional ABE fermentation process is economically unfavourable, novel butanol production strains are being developed. In this review, some newly engineered solvent-producing Clostridium strains are described and strains of which sequences are available are compared with C. acetobutylicum. Furthermore, the past and present of commercial butanol fermentation are presented, including active plants and companies. Finally, the use of biomass as substrate for butanol production is discussed. Some advances concerning processing of biomass in a biorefinery are highlighted, which would allow lowering the price of the butanol fermentation process at industrial scale.