Enhancing butanol production with Clostridium pasteurianum CH4 using sequential glucose-glycerol addition and simultaneous dual-substrate cultivation strategies

Mildly acidic pH boosts up CO2 conversion to isobutyrate in H2 driven gas fermentation system

As a greenhouse gas, massive carbon dioxide (CO2) has been generated due to organic matter degradation in wastewater treatment processes. Microbial gas fermentation offers a promising approach to capture CO2 and generate various valuable chemicals. However, limited studies have achieved branched or medium-chain fatty acids production via gas fermentation. This study reported the production of isobutyrate and hexanoate by feeding H2 and CO2 into membrane biofilm reactors (MBfRs). The gas fermentation product in the reactor with neutral pH (pH of 7) was dominated by acetate (accounting for 90 % of the product spectrum), whereas a mildly acidic pH (pH of 6) resulted in isobutyrate and hexanoate as the dominant products, with a selectivity of 57 % and 42 %, respectively. Notably, a remarkably high concentration of isobutyrate (266 mmol C/L) was produced in the reactor with pH of 6. Subsequent batch test results suggest that the isobutyrate production in this study is coupled with acetogenesis and ethanol-driven chain elongation processes, rather than via methanol-driven chain elongation reported previously. High-throughput 16S rRNA gene amplicon sequencing revealed that the microbial community under neutral pH was dominated by acetate-producing homoacetogens Acetobacterium. By contrast, a mildly acidic pH promoted the community shifting towards chain elongation microorganisms, dominated by Clostridium sensu stricto 12, Oscillibacter and Caproiciproducens. Collectively, this study demonstrates the significant role of mildly acidic pH in boosting up bioisomerization and chain elongation in gas fermentation systems, thus triggering isobutyrate and hexanoate production. The findings highlight gas fermentation as a new green alternative route for generating highly valuable isobutyrate and hexanoate.

Enhanced enzymatic sugar production from corn stover by combination of water extraction and glycerol-assisted instant catapult steam explosion

Glycerol-assisted instant catapult steam explosion (ICSE) of lignocellulose is an effective pretreatment method for enhancing sugar production compared to glycerol-free ICSE. In this study, glycerol-assisted ICSE of corn stover was studied in order to understand the reaction mechanisms and further optimize the process. Results showed that water extraction of corn stover prior to ICSE reduced pseudo-lignin formation. The combination of water extraction and glycerol-assisted ICSE led to the formation of lignin with a lower molecular weight (Mw) of 2851 g/mol than 3521 g/mole of that from the combination of water extraction and glycerol-free ICSE. 1H-13C NMR analysis revealed that glycerol likely reacted with lignin carboxylic OHs through esterification while etherification of aliphatic OHs was not observed in ICSE. These lignin analyses indicated that glycerol protected lignin from condensation/repolymerization during glycerol-assisted ICSE. Enzymatic hydrolysis results showed that without water extraction increasing glycerol usage from 0.2 kg/kg stover to 0.4 kg/kg stover improved glucan digestibility to 78% but further increase to 0.5 kg/kg stover reduced glucan digestibility. In addition, at the glycerol usage of 0.2-0.4 kg/kg stover, washing of pretreated stover for removal of glycerol and other biomass-derived compounds did not improve glucan digestibility compared to unwashed ones. Combination of water extraction and glycerol-assisted ICSE led to a high glucan digestibility of 89.7% and a total glucose yield of 25.5 g glucose/100 g stover, which were 30.1% and 7.5 g/100 g stover higher than those derived from glycerol-free ICSE of stover, respectively. Since glycerol is a low-cost carbon source, the resulting enzymatic hydrolysate that contained both glucose and glycerol may be directly used to produce bioproducts by microbial fermentation.

Potential of butanol production from Thailand marine macroalgae using Clostridium beijerinckii ATCC 10132-based ABE fermentation

The economical bio-butanol-based fermentation process is mainly limited by the high price of first-generation biomass, which is an intensive cost for the pretreatment of second-generation biomass. As third-generation biomass, marine macroalgae could be potentially advantageous for conversion to clean and renewable bio-butanol through acetone-butanol-ethanol (ABE) fermentation. In this study, butanol production from three macroalgae species (Gracilaria tenuistipitata, Ulva intestinalis, and Rhizoclonium sp.) by Clostridium beijerinckii ATCC 10132 was assessed comparatively. The enriched C beijerinckii ATCC 10132 inoculum produced a high butanol concentration of 14.07 g L-1 using 60 g L-1 of glucose. Among the three marine seaweed species, G. tenuistipitata exhibited the highest potential for butanol production (1.38 g L-1 ). Under the 16 conditions designed using the Taguchi method for low-temperature hydrothermal pretreatment (HTP) of G. tenuistipitata, the maximum reducing sugar yield rate of 57.6% and ABE yield of 19.87% were achieved at a solid to liquid (S/L) ratio of 120, temperature of 110°C, and holding time of 10 min (Severity factor, R0 1.29). In addition, pretreated G. tenuistipitata could be converted to 3.1 g L-1 of butanol using low-HTP at an S/L ratio of 50 g L-1 , temperature of 80°C (R0 0.11), and holding time of 5 min.

A Focus on the Transformation Processes for the Valorization of Glycerol Derived from the Production Cycle of Biofuels

Glycerol is a valuable by-product in the biodiesel industries. However, the increase in biodiesel production resulted in an excess production of glycerol, with a limited market compared to its availability. Precisely because glycerol became a waste to be disposed of, the costs of biodiesel production have reduced. From an environmental point of view, identifying reactions that can convert glycerol into new products that can be reused in different applications has become a real necessity. According to the unique structural characteristics of glycerol, transformation processes can lead to different chemical functionalities through redox reactions, dehydration, esterification, and etherification, with the formation of products that can be applied both at the finest chemical level and to bulk chemistry.

Increased Selectivity for Butanol in Clostridium Pasteurianum Fermentations via Butyric Acid Addition or Dual Feedstock Strategy

Volatility of the petroleum market has renewed research into butanol as an alternate fuel. In order to increase the selectivity for butanol during glycerol fermentation with Clostridium pasteurianum, butyric acid can be added to the medium. In this manuscript, different methods of extracellular butyric acid addition are explored, as well as self-generation of butyric acid fermented from sugars in a co-substrate strategy. Molasses was used as an inexpensive sugar substrate, and the optimal molasses to glycerol ratio was found to allow the butyric acid to be taken back up into the cells and increase the productivity of butanol from all carbon sources. When butyric acid is added directly into the media, there was no significant difference between chemically pure butyric acid, or butyric acid rich supernatant from a separate fermentation. When low concentrations of butyric acid (1 or 2 g/L) are added to the initial media, an inhibitory effect is observed, with no influence on the butanol selectivity. However, when added later to the fermentation, over 1 g/L butyric acid is taken into the cells and increased the relative carbon yield from 0.449 to 0.519 mols carbon in product/mols carbon in substrate. An optimized dual substrate fermentation strategy in a pH-controlled reactor resulted in the relative carbon yield rising from 0.439 when grown on solely glycerol, to 0.480 mols C product/mols C substrate with the dual substrate strategy. An additional benefit is the utilization of a novel source of sugars to produce butanol from C. pasteurianum. The addition of butyric acid, regardless of how it is generated, under the proper conditions can allow for increased selectivity for butanol from all substrates.

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.

Increased Butanol Yields through Cosubstrate Fermentation of Jerusalem Artichoke Tubers and Crude Glycerol by Clostridium pasteurianum DSM 525

Clostridium pasteurianum DSM 525 can produce butanol, 1,3-propanediol, and ethanol from glycerol. The product distribution can be tilted toward butanol when adding butyric acid. The strain predominantly produces acetic and butyric acids when grown on saccharides. Hence, butyrate formed from saccharide conversion can be used to stimulate butanol production from glycerol under cosubstrate cultivation. The optimal cosubstrate ratio was determined, and under optimal conditions, a butanol yield and a productivity of 0.27 ± 0.01 g_butanol g^-1 _{(glycerol + sugar)} ^-1 and 0.74 ± 0.02 g L^-1 h^-1 were obtained. On the basis of these results, batch fermentation in a 5 L bioreactor was performed using Jerusalem artichoke hydrolysate (carbohydrate source) and crude glycerol (residue from biodiesel production) at the previously determined optimal condition. A butanol yield and a productivity of 0.28 ± 0.007 g_butanol g_{(glycerol+sugar)} ^-1 and 0.55 ± 0.008 g L^-1 h^-1 were achieved after 27 h fermentation, indicating the suitability of those low-cost carbon sources as cosubstrates for butanol production via C. pasteurianum.

Nutrient modulation based process engineering strategy for improved butanol production from Clostridium acetobutylicum

The present study demonstrates a process engineering strategy to achieve high butanol titer and productivity from wild type Clostridium acetobutylicum MTCC 11274. In the first step, two different media were optimized with the objectives of maximizing the biomass and butanol productivity, respectively. In the next step, attributes of these two media compositions were integrated to design a two-stage fed-batch process which resulted in maximal butanol productivity of 0.55 g L^-1 h^-1 with titer of 13.1 g L^-1 . Further, two-stage fed-batch process along with combinatorial use of magnesium limitation and calcium supplementation resulted in the highest butanol titer and productivity of 16.5 g L^-1 and 0.59 g L^-1 h^-1 , respectively. Finally, integration of the process with gas stripping and modulation of feeding duration resulted in a cumulative butanol titer of 54.3 g L^-1 and productivity of 0.58 g L^-1 h^-1 . The strategy opens up possibility of developing a viable butanol bioprocess. © 2019 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2771, 2019.

Metabolic and proteomic analyses of product selectivity and redox regulation in Clostridium pasteurianum grown on glycerol under varied iron availability

BACKGROUND

Clostridium pasteurianum as an emerging new microbial cell factory can produce both n-butanol (BuOH) and 1,3-propanediol (1,3-PDO), and the pattern of product formation changes significantly with the composition of the culture medium. Among others iron content in the medium was shown to strongly affect the products selectivity. However, the mechanism behind this metabolic regulation is still unclear. For a better understanding of such metabolic regulation and for process optimization, we carried out fermentation experiments under either iron excess or iron limitation conditions, and performed metabolic, stoichiometric and proteomic analyses.

RESULTS

1,3-PDO is most effectively produced under iron limited condition (Fe-), whereas 1,3-PDO and BuOH were both produced under iron rich condition (Fe+). With increased iron availability the BuOH/1,3-PDO ratio increased significantly from 0.27 mol/mol (at Fe-) to 1.4 mol/mol (at Fe+). Additionally, hydrogen production was enhanced significantly under Fe+ condition. Proteomic analysis revealed differentiated expression of many proteins including several ones of the central carbon metabolic pathway. Among others, pyruvate: ferredoxin oxidoreductase, hydrogenases, and several electron transfer flavoproteins was found to be strongly up-regulated under Fe+ condition, pointing to their strong involvement in the regeneration of the oxidized form of ferredoxin, and consequently their influences on the product selectivity in C. pasteurianum. Of particular significance is the finding that H2 formation in C. pasteurianum is coupled to the ferredoxin-dependent butyryl-CoA dehydrogenase catalyzed reaction, which significantly affects the redox balance and thus the product selectivity.

CONCLUSIONS

The metabolic, stoichiometric and proteomic results clearly show the key roles of hydrogenases and ferredoxins dependent reactions in determining the internal redox balance and hence product selectivity. Not only the NADH pool but also the regulation of the ferredoxin pool could explain such product variation under different iron conditions.

Substrate dependent modulation of butanol to ethanol ratio in non-acetone forming Clostridium sporogenes NCIM 2918

Present study reports a non-acetone producing Clostridium sporogenes strain as a potential producer of liquid biofuels. Alcohol production was positively regulated by sorbitol and instant dry yeast as carbon and nitrogen sources respectively. Media optimization resulted in maximum butanol and ethanol titer (gL^-1) of 12.1 and 7.9 respectively. Depending on the combination of carbon sources, the organism was found to manipulate its metabolism towards synthesis of either ethanol or butanol, thereby affecting the total alcohol titer. Among various dual substrate combinations, glucose-glycerol mixture in the ratio of 60:40 resulted in maximum butanol and ethanol titer (gL^-1) of 11.9 and 12.1 respectively with total alcohol productivity of 0.59gL^-1h^-1. In the mixture, when pure glycerol was replaced with crude glycerol, butanol and ethanol titer (gL^-1) of 11.2 and 11.7 was achieved. Hence, the strain shows immense potential for biofuels production using crude glycerol as cheap substrate.

Towards improved butanol production through targeted genetic modification of Clostridium pasteurianum

Declining fossil fuel reserves, coupled with environmental concerns over their continued extraction and exploitation have led to strenuous efforts to identify renewable routes to energy and fuels. One attractive option is to convert glycerol, a by-product of the biodiesel industry, into n-butanol, an industrially important chemical and potential liquid transportation fuel, using Clostridium pasteurianum. Under certain growth conditions this Clostridium species has been shown to predominantly produce n-butanol, together with ethanol and 1,3-propanediol, when grown on glycerol. Further increases in the yields of n-butanol produced by C. pasteurianum could be accomplished through rational metabolic engineering of the strain. Accordingly, in the current report we have developed and exemplified a robust tool kit for the metabolic engineering of C. pasteurianum and used the system to make the first reported in-frame deletion mutants of pivotal genes involved in solvent production, namely hydA (hydrogenase), rex (Redox response regulator) and dhaBCE (glycerol dehydratase). We were, for the first time in C. pasteurianum, able to eliminate 1,3-propanediol synthesis and demonstrate its production was essential for growth on glycerol as a carbon source. Inactivation of both rex and hydA resulted in increased n-butanol titres, representing the first steps towards improving the utilisation of C. pasteurianum as a chassis for the industrial production of this important chemical.

Value-added processing of crude glycerol into chemicals and polymers

Crude glycerol is a low-value byproduct which is primarily obtained from the biodiesel production process. Its composition is significantly different from that of pure glycerol. Crude glycerol usually contains various impurities, such as water, methanol, soap, fatty acids, and fatty acid methyl esters. Considerable efforts have been devoted to finding applications for converting crude glycerol into high-value products, such as biofuels, chemicals, polymers, and animal feed, to improve the economic viability of the biodiesel industry and overcome environmental challenges associated with crude glycerol disposal. This article reviews recent advances of biological and chemical technologies for value-added processing of crude glycerol into chemicals and polymers, and provides strategies for addressing production challenges.

Fermentation of mixed substrates by Clostridium pasteurianum and its physiological, metabolic and proteomic characterizations

Background

Clostridium pasteurianum is becoming increasingly attractive for the production of chemicals and fuels such as n-butanol and 1,3-propanediol. Previously we have shown that dual substrate fermentation using glucose and glycerol enhanced the cell growth and butanol production significantly. Although C. pasteurianum can grow efficiently with either glucose or glycerol alone, under certain conditions, glucose limitation in the mixed substrate fermentation leads to growth cessation. To understand this phenomenon and for process optimization, fermentation experiments were performed in the presence of excess glycerol but with varied initial concentrations of glucose which were followed by physiological, metabolic and proteomic analyses.

Results

Physiological characterization showed that the observed cease of growth is not due to the toxicity of n-butanol. Furthermore, the growth can be resumed by addition of glucose or the intermediate oxaloacetate. Proteomic analysis shed more light on the system-level regulation of many proteins directly or indirectly associated with this phenomenon. Surprisingly, it is found that the specific growth rate of C. pasteurianum in the different growth phases (e.g. before and after glucose limitation) correlated well with the expression level of the ATP dependent pyruvate carboxylase and with the expression level of biotin synthase which provides the cofactor biotin for the formation of oxaloacetate from pyruvate. Bioenergetic analysis based on the formation rates of metabolites further show that ATP supply is not a limiting factor for the pyruvate carboxylation to oxaloacetate.

Conclusions

The results of physiological and proteomic analyses clearly show that the anaplerotic synthesis of oxaloacetate plays a key role in determining the growth behaviour of C. pasteurianum in fermentations with mixed substrates of glucose and glycerol. This study provides interesting targets for metabolic engineering of this emerging industrial microorganism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0497-4) contains supplementary material, which is available to authorized users.

The role of 1,3-propanediol production in fermentation of glycerol by Clostridium pasteurianum

Waste crude glycerol from biodiesel production can be used to produce biobutanol using Clostridium pasteurianum with the main products being n-butanol, 1,3-propanediol (PDO) and ethanol. There has been much discrepancy and mystery around the cause and effect of process parameters on the product distribution, thus a better understanding of the pathway regulation is required. This study shows that as process pH decreased, the rate of cell growth and CO2 production also decreased, resulting in slower fermentations, increased duration of butanol production and higher butanol concentrations and yields. The production rate of PDO was multi-modal and the role of PDO appears to function in redox homeostasis. The results also showed that C. pasteurianum displayed little biphasic behavior when compared to Clostridia spp. typically used in ABE fermentation due to the alternative glycolysis-independent reductive pathway of PDO production, rendering it suitable for a continuous fermentation process.

Effective isopropanol-butanol (IB) fermentation with high butanol content using a newly isolated Clostridium sp. A1424

BACKGROUND

Acetone-butanol-ethanol fermentation has been studied for butanol production. Alternatively, to achieve acetone-free butanol production, use of clostridium strains producing butanol and 1,3-propanediol (1,3-PDO) from glycerol, natural and engineered isopropanol-butanol-ethanol (IBE) producers has been attempted; however, residual 1,3-PDO and acetone, low IBE production by natural IBE producers, and complicated gene modification are limitations.

RESULTS

Here, we report an effective isopropanol and butanol (IB) fermentation using a newly isolated Clostridium sp. A1424 capable of producing IB from various substrates with a small residual acetone. Notably, this strain also utilized glycerol and produced butanol and 1,3-PDO. After 46.35 g/L of glucose consumption at pH 5.5-controlled batch fermentation, Clostridium sp. A1424 produced 9.43 g/L of butanol and 13.92 g/L of IB at the productivity of 0.29 and 0.44 g/L/h, respectively, which are the highest values in glucose-based batch fermentations using natural IB producers. More interestingly, using glucose-glycerol mixtures at ratios ranging from 20:2 to 14:8 led to not only acetone-free and 1,3-PDO-free IB fermentation but also enhanced IB production along with a much higher butanol content (butanol/isopropanol ratio of 1.81 with glucose vs. 2.07-6.14 with glucose-glycerol mixture). Furthermore, when the mixture of glucose and crude glycerol at the ratio of 14:8 (total concentration of 35.68 g/L) was used, high butanol/isopropanol ratio (3.44) and butanol titer (9.86 g/L) were achieved with 1.4-fold enhanced butanol yield (0.28 g/g) and productivity (0.41 g/L/h) compared to those with glucose only at pH 5.5.

CONCLUSIONS

A newly isolated Clostridium sp. A1424 was able to produce butanol and isopropanol from various carbon sources. The productivity and titer of butanol and total alcohol obtained in this study were higher than the previously reported results obtained using other natural IB producers. Use of the mixture of glucose and glycerol was successful to achieve acetone-free, 1,3-PDO-free, and enhanced IB production with higher yield, productivity, and selectivity of butanol compared to those with glucose only, providing great advantages from the perspective of carbon recovery to alcohols. This notable result could be accomplished by isolating an effective IB producer Clostridium sp. A1424 as well as by utilizing glucose-glycerol mixtures.

Bio-butanol production from glycerol with Clostridium pasteurianum CH4: the effects of butyrate addition and in situ butanol removal via membrane distillation

BACKGROUND

Clostridium pasteurianum CH4 was used to produce butanol from glycerol. The performance of butanol fermentation was improved by adding butyrate as the precursor to trigger the metabolic pathway toward butanol production, and by combining this with in situ butanol removal via vacuum membrane distillation (VMD) to avoid the product inhibition arising from a high butanol concentration.

RESULTS

Adding 6 g L(-1) butyrate as precursor led to an increase in the butanol yield from 0.24 to 0.34 mol butanol (mol glycerol)(-1). Combining VMD and butyrate addition strategies could further enhance the maximum effective butanol concentration to 29.8 g L(-1), while the yield was also improved to 0.39 mol butanol (mol glycerol)(-1). The butanol concentration in the permeate of VMD was nearly five times higher than that in the feeding solution.

CONCLUSIONS

The proposed butyrate addition and VMD in situ butanol removal strategies are very effective in enhancing both butanol titer and butanol yield. This would significantly enhance the economic feasibility of fermentative production of butanol. The VMD-based technology not only alleviates the inhibitory effect of butanol, but also markedly increases butanol concentration in the permeate after condensation, thereby making downstream processing easier and more cost-effective.

Improved n-butanol production by a non-acetone producing Clostridium pasteurianum DSMZ 525 in mixed substrate fermentation

The kinetics of growth, acid and solvent production in batch culture of Clostridium pasteurianum DSMZ 525 were examined in mixed or mono-substrate fermentations. In pH-uncontrolled batch cultures, the addition of butyric acid or glucose significantly enhanced n-butanol production and the ratio of butanol/1,3-propanediol. In pH-controlled batch culture at pH = 6, butyric acid addition had a negative effect on growth and did not lead to a higher n-butanol productivity. On the other hand, mixed substrate fermentation using glucose and glycerol enhanced the growth and acid production significantly. Glucose limitation in the mixed substrate fermentation led to the reduction or inhibition of the glycerol consumption by the growing bacteria. Therefore, for the optimal growth and n-butanol production by C. pasteurianum, a limitation of either substrate should be avoided. Under optimized batch conditions, n-butanol concentration and maximum productivity achieved were 21 g/L, and 0.96 g/L × h, respectively. In comparison, mixed substrate fermentation using biomass hydrolysate and glycerol gave a n-butanol concentration of 17 g/L with a maximum productivity of 1.1 g/L × h. In terms of productivity and final n-butanol concentration, the results demonstrated that C. pasteurianum DSMZ 525 is well suitable for n-butanol production from mixed substrates of biomass hydrolysate and glycerol and represents an alternative promising production strain.

Reducing cofactors contribute to the increase of butanol production by a wild-type Clostridium sp. strain BOH3

Availability of reducing factors (e.g., NADH and NADPH) plays an important role in improving the efficacy of products conversion in cofactor-dependent production systems. In this study, nicotinic acid (NA), the precursor of NADH and NADPH, was supplemented to the growth medium of a wild-type Clostridium sp. strain BOH3. Results showed that the addition of precursor NA to the medium led to a significant increase in the levels of NADH and NADPH. Meanwhile, a maximal cell growth rate and butanol generation rate were reached by applying a two-stage pH-shift strategy, achieving 18.7g/L butanol with a yield of 24.6% and a productivity of 0.26g/Lh. The metabolic patterns were shifted towards more reduced metabolites as reflected by higher butanol-to-acetone ratio (11%) and butanol-to-acid ratio (292%). Redistributing metabolic flux to butanol via manipulations of reducing cofactor and pH shift could become an alternative tool to realize metabolic engineering goals.

Fermentation approach for enhancing 1-butanol production using engineered butanologenic Escherichia coli

In this study, engineered butanologenic Escherichia coli T5 constructed by the OGAB method was used for 1-butanol production. The results showed the feasibility of the artificial butanologenic operon, (Promoter Pr)-thil-crt-bcd-etfB-etfA-hbd-adhe1-adhe, where the 1-butanol titer, specific BuOH yield, and BuOH yield were 4.50 mg/L, 4.50 mg-BuOH/g cell, and 0.35 mg-BuOH/g-glucose, respectively. Fermentation conditions of anaerobic, low initial concentrations of carbon sources, low oxidation state of carbon source, pH of 6, addition of glutathione and citrate, had been shown for efficiently improving the 1-butanol production. The premise behind these fermentation approaches can be categorized into two lines of reasoning, either elevated the availability of acetyl-CoA or lowered the intracellular redox state. By comparing the fermentation conditions tested in this study, pH has been shown to be the most efficiency strategies for 1-butanol production while the replacement of glucose with glycerol provides the highest improvement in butanol yield.

Draft Genome Sequence of Type Strain Clostridium pasteurianum DSM 525 (ATCC 6013), a Promising Producer of Chemicals and Fuels

Clostridium pasteurianum, an anaerobic bacterium able to utilize atmospheric free nitrogen for biosynthesis, has recently been proven to be a promising producer of chemicals and fuels, such as 1,3-propanediol and n-butanol. Here, we report the high-quality draft genome sequence of DSM 525, a type strain of C. pasteurianum.