Butyric acid fermentation in a fibrous bed bioreactor with immobilized Clostridium tyrobutyricum from cane molasses

Butyric acid production from lignocellulosic biomass hydrolysates by engineered Clostridium tyrobutyricum overexpressing xylose catabolism genes for glucose and xylose co-utilization

Clostridium tyrobutyricum can utilize glucose and xylose as carbon source for butyric acid production. However, xylose catabolism is inhibited by glucose, hampering butyric acid production from lignocellulosic biomass hydrolysates containing both glucose and xylose. In this study, an engineered strain of C. tyrobutyricum Ct-pTBA overexpressing heterologous xylose catabolism genes (xylT, xylA, and xylB) was investigated for co-utilizing glucose and xylose present in hydrolysates of plant biomass, including soybean hull, corn fiber, wheat straw, rice straw, and sugarcane bagasse. Compared to the wild-type strain, Ct-pTBA showed higher xylose utilization without significant glucose catabolite repression, achieving near 100% utilization of glucose and xylose present in lignocellulosic biomass hydrolysates in bioreactor at pH 6. About 42.6g/L butyrate at a productivity of 0.56g/L·h and yield of 0.36g/g was obtained in batch fermentation, demonstrating the potential of C. tyrobutyricum Ct-pTBA for butyric acid production from lignocellulosic biomass hydrolysates.

Bostrycin production by agro-industrial residues and its potential for food processing

Bostrycin, a red antibacterial agent produced by Nigrospora sp. no. 407, is considered for meat processing. To optimize production, the culture conditions of submerged fermentation (SmF) and solid-state fermentation (SSF) were investigated. The optimal SmF conditions were a medium containing 1.0% cane molasses and incubation at 30 °C and 150 rpm for 6 days. In SSF, other than bostrycin, less pigment was produced and the optimal ratio of bagasse to water was 1:2 for 10 days. The production and recovery rate of bostrycin by SmF were 120 mg/L and 40%, respectively. Bostrycin exhibited thermostable, pH-dependent color change and dose-dependent antibacterial activity against Clostridium botulinum. Bostrycin-modified meat turned strong red for at least 24 h and could not be removed by washing; bostrycin maintained its antibacterial activity with a bacteriostasis rate of 91% on Staphylcoccus aureus. This is an easy and inexpensive means of acquiring bostrycin from molasses and sugarcane.

Insights from the complete genome sequence of Clostridium tyrobutyricum provide a platform for biotechnological and industrial applications

Genetic research enables the evolution of novel biochemical reactions for the production of valuable chemicals from environmentally-friendly raw materials. However, the choice of appropriate microorganisms to support these reactions, which must have strong robustness and be capable of a significant product output, is a major difficulty. In the present study, the complete genome of the Clostridium tyrobutyricum strain CCTCC W428, a hydrogen- and butyric acid-producing bacterium with increased oxidative tolerance was analyzed. A total length of 3,011,209 bp of the C. tyrobutyricum genome with a GC content of 31.04% was assembled, and 3038 genes were discovered. Furthermore, a comparative clustering of proteins from C. tyrobutyricum CCTCC W428, C. acetobutylicum ATCC 824, and C. butyricum KNU-L09 was conducted. The results of genomic analysis indicate that butyric acid is produced by CCTCC W428 from butyryl-CoA through acetate reassimilation via CoA transferase, instead of the well-established phosphotransbutyrylase-butyrate kinase pathway. In addition, we identified ten proteins putatively involved in hydrogen production and 21 proteins associated with CRISPR systems, together with 358 ORFs related to ABC transporters and transcriptional regulators. Enzymes, such as oxidoreductases, HNH endonucleases, and catalase, were also found in this species. The genome sequence illustrates that C. tyrobutyricum has several desirable traits, and is expected to be suitable as a platform for the high-level production of bulk chemicals as well as bioenergy.

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.

High efficiency succinic acid production from glycerol via in situ fibrous bed bioreactor with an engineered Yarrowia lipolytica

In this study, in situ fibrous bed bioreactor (isFBB) was developed at the first time for efficient succinic acid (SA) production by Yarrowia lipolytica. After optimization, SA titer, productivity and yield of 51.9g/L, 1.46g/L/h and 0.42g/g were obtained respectively via isFBB fermentation under conditions of 750cm² cotton towel, 120g/L initial glycerol and 3L/min aeration rate. By fed batch strategy, SA titer raised up to 198.2g/L was achieved, which was the highest value ever reported. In operation stability study, SA productivity showed no obvious decrease after 12 repeated batches of 460h fermentation, and cell viability even recovered within two repeated batches after intentional interruption. This study successfully attained a highly efficient and stable isFBB for enhanced SA production by Y. lipolytica.

Microbial Production of Short Chain Fatty Acids from Lignocellulosic Biomass: Current Processes and Market

Biological production of organic acids from conversion of biomass derivatives has received increased attention among scientists and engineers and in business because of the attractive properties such as renewability, sustainability, degradability, and versatility. The aim of the present review is to summarize recent research and development of short chain fatty acids production by anaerobic fermentation of nonfood biomass and to evaluate the status and outlook for a sustainable industrial production of such biochemicals. Volatile fatty acids (VFAs) such as acetic acid, propionic acid, and butyric acid have many industrial applications and are currently of global economic interest. The focus is mainly on the utilization of pretreated lignocellulosic plant biomass as substrate (the carbohydrate route) and development of the bacteria and processes that lead to a high and economically feasible production of VFA. The current and developing market for VFA is analyzed focusing on production, prices, and forecasts along with a presentation of the biotechnology companies operating in the market for sustainable biochemicals. Finally, perspectives on taking sustainable product of biochemicals from promise to market introduction are reviewed.

The acquisition of Clostridium tyrobutyricum mutants with improved bioproduction under acidic conditions after two rounds of heavy-ion beam irradiation

End-product inhibition is a key factor limiting the production of organic acid during fermentation. Two rounds of heavy-ion beam irradiation may be an inexpensive, indispensable and reliable approach to increase the production of butyric acid during industrial fermentation processes. However, studies of the application of heavy ion radiation for butyric acid fermentation engineering are lacking. In this study, a second ¹²C⁶⁺ heavy-ion irradiation-response curve is used to describe the effect of exposure to a given dose of heavy ions on mutant strains of Clostridium tyrobutyricum. Versatile statistical elements are introduced to characterize the mechanism and factors contributing to improved butyric acid production and enhanced acid tolerance in adapted mutant strains harvested from the fermentations. We characterized the physiological properties of the strains over a large pH value gradient, which revealed that the mutant strains obtained after a second round of radiation exposure were most resistant to harsh external pH values and were better able to tolerate external pH values between 4.5 and 5.0. A customized second round of heavy-ion beam irradiation may be invaluable in process engineering.

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.

Deciphering Clostridium tyrobutyricum Metabolism Based on the Whole-Genome Sequence and Proteome Analyses

Clostridium tyrobutyricum is a Gram-positive anaerobic bacterium that efficiently produces butyric acid and is considered a promising host for anaerobic production of bulk chemicals. Due to limited knowledge on the genetic and metabolic characteristics of this strain, however, little progress has been made in metabolic engineering of this strain. Here we report the complete genome sequence of C. tyrobutyricum KCTC 5387 (ATCC 25755), which consists of a 3.07-Mbp chromosome and a 63-kbp plasmid. The results of genomic analyses suggested that C. tyrobutyricum produces butyrate from butyryl-coenzyme A (butyryl-CoA) through acetate reassimilation by CoA transferase, differently from Clostridium acetobutylicum, which uses the phosphotransbutyrylase-butyrate kinase pathway; this was validated by reverse transcription-PCR (RT-PCR) of related genes, protein expression levels, in vitro CoA transferase assay, and fed-batch fermentation. In addition, the changes in protein expression levels during the course of batch fermentations on glucose were examined by shotgun proteomics. Unlike C. acetobutylicum, the expression levels of proteins involved in glycolytic and fermentative pathways in C. tyrobutyricum did not decrease even at the stationary phase. Proteins related to energy conservation mechanisms, including Rnf complex, NfnAB, and pyruvate-phosphate dikinase that are absent in C. acetobutylicum, were identified. Such features explain why this organism can produce butyric acid to a much higher titer and better tolerate toxic metabolites. This study presenting the complete genome sequence, global protein expression profiles, and genome-based metabolic characteristics during the batch fermentation of C. tyrobutyricum will be valuable in designing strategies for metabolic engineering of this strain.

IMPORTANCE

Bio-based production of chemicals from renewable biomass has become increasingly important due to our concerns on climate change and other environmental problems. C. tyrobutyricum has been used for efficient butyric acid production. In order to further increase the performance and expand the capabilities of this strain toward production of other chemicals, metabolic engineering needs to be performed. For this, better understanding on the metabolic and physiological characteristics of this bacterium at the genome level is needed. This work reporting the results of complete genomic and proteomic analyses together with new insights on butyric acid biosynthetic pathway and energy conservation will allow development of strategies for metabolic engineering of C. tyrobutyricum for the bio-based production of various chemicals in addition to butyric acid.

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.

Feasibility of various carbon sources and plant materials in enhancing the growth and biomass productivity of the freshwater microalgae Monoraphidium griffithii NS16

In order to assess the feasibility of various carbon sources and plant materials in increasing the growth rate and biomass productivity of Monoraphidium griffithii, ten carbon sources as well as six plant materials were tested in mixotrophic cultures with or without aeration. It was found that glucose, fructose, maltose, sodium acetate and mannitol were potential carbon sources for growth enhancement of M. griffithii. Supplementation of culture medium with these carbon sources resulted in approximately 1-4-fold increase in cell density compared to control in a small scale culture. In a larger scale mixotrophic culture with aeration, 0.05% mannitol and 0.1% fructose resulted in a decent 1-1.5-fold increase in final cell density, approximately 2-fold increase in growth rate and 0.5-1-fold increase in dry biomass weight. Findings from this study suggests that glucose, fructose, maltose and mannitol were potential organic carbon sources for mixotrophic culture of M. griffithii.

Butyric acid fermentation from pretreated and hydrolysed wheat straw by an adapted Clostridium tyrobutyricum strain

Butyric acid is a valuable building-block for the production of chemicals and materials and nowadays it is produced exclusively from petroleum. The aim of this study was to develop a suitable and robust strain of Clostridium tyrobutyricum that produces butyric acid at a high yield and selectivity from lignocellulosic biomasses. Pretreated (by wet explosion) and enzymatically hydrolysed wheat straw (PHWS), rich in C6 and C5 sugars (71.6 and 55.4 g l⁻¹ of glucose and xylose respectively), was used as substrate. After one year of serial selections, an adapted strain of C. tyrobutyricum was developed. The adapted strain was able to grow in 80% (v v⁻¹) PHWS without addition of yeast extract compared with an initial tolerance to less than 10% PHWS and was able to ferment both glucose and xylose. It is noticeable that the adapted C. tyrobutyricum strain was characterized by a high yield and selectivity to butyric acid. Specifically, the butyric acid yield at 60–80% PHWS lie between 0.37 and 0.46 g g⁻¹ of sugar, while the selectivity for butyric acid was as high as 0.9–1.0 g g⁻¹ of acid. Moreover, the strain exhibited a robust response in regards to growth and product profile at pH 6 and 7.

Continuous Fermentation of Wheat Straw Hydrolysate by Clostridium tyrobutyricum with In-Situ Acids Removal

The present study focused on fermentative butyric acid production by Clostridium tyrobutyricum from pre-treated and hydrolysed wheat straw (PHWS) based on continuous operation mode and in situ acids extraction by reverse electro enhanced dialysis (REED). Different dilutions of PHWS in a synthetic medium (60-100 % v/v) were tested. It was found that continuous fermentation of PHWS greatly enhanced the sugar consumption rates and butyric acid productivity compared to batch tests, while application of REED enhanced them even further. Specifically, applying combined continuous operation mode and REED system for the fermentation of 70 % PHWS resulted in 19- and 53-fold higher glucose (1.37 g L^-1 h^-1) and xylose (0.80 g L^-1 h^-1) consumption rates, respectively, compared to those obtained by batch processing. Fermentation of 100 % PHWS continued unhindered with just urea and K₂HPO₄ added with butyric acid production rate, yield and selectivity being 1.30 g L^-1 h^-1, 0.45 g g^-1 sugars and 0.88 g g^-1 acids, respectively. These results were also confirmed in a 20 L pilot plant bioreactor system.

Enhanced butanol production by immobilized Clostridium beijerinckii TISTR 1461 using zeolite 13X as a carrier

Butanol production by cell immobilization onto porous materials-brick and zeolite 13X-was investigated using Clostridium beijerinckii TISTR 1461. Characterization results of two materials were completed to evaluate their potential as an immobilization carrier. Although zeolite has greater porosity than brick, it cannot be used for cell aggregation without treating with chemical. After immobilization, both materials can enhance butanol titers from 5.29 to 5.80g/L and 8.58g/L using brick and zeolite, respectively. Butanol to glucose yield also improved from 0.14 to 0.16g/g after immobilization. It was found that butanol production significantly increased due to an increase in buffering capacity, strong bonding between the zeolite surface and cell, and butanol tolerance. In addition, repeated batch fermentation was performed, demonstrating that cells immobilized onto zeolite 13X have high stability and potential for long-term use in continuous fermentation.

Comparison of the effects of high energy carbon heavy ion irradiation and Eucommia ulmoides Oliv. on biosynthesis butyric acid efficiency in Clostridium tyrobutyricum

Clostridium tyrobutyricum is well documented as a fermentation strain for the production of butyric acid. In this work, using high-energy carbon heavy ion irradiated C. tyrobutyricum, then butyric acid fermentation using glucose or alkali and acid pretreatments of Eucommia ulmoides Oliv. as a carbon source was carried out. Initially, the modes at pH 5.7-6.5 and 37°C were compared using a model medium containing glucose as a carbon source. When the 72gL(-1) glucose concentration was found to be the highest yield, the maximum butyric acid production from glucose increased significantly, from 24gL(-1) for the wild type strains to 37gL(-1) for the strain irradiated at 126AMeV and a dose of 35Gy and a 10(7)ions/pulse. By feeding 100gL(-1) acid pretreatments of E. ulmoides Oliv. into the fermentations, butyrate yields (5.8gL(-1)) and butyrate/acetate (B/A) ratio (4.32) were achieved.

Continuous ethanol production from sugarcane molasses using a newly designed combined bioreactor system by immobilized Saccharomyces cerevisiae

Continuous ethanol fermentation using polyvinyl alcohol (PVA), immobilized yeast, and sugarcane molasses (22 and 35°Bx) with 8 g/L urea was run in a combined bioreactor system consisting of three-stage tubular bioreactors in series. The effect of the dilution rate (D) at 0.0037, 0.0075, 0.0117, 0.0145, 0.018, and 0.0282 H(-1) on continuous ethanol fermentation was investigated in this study. The results showed that D had a significant effect on fermentation efficiency, sugar-utilized rate, ethanol yield, and ethanol productivity in this designed continuous fermentation system. The D had a linear relationship with residual sugar and ethanol production under certain conditions. The highest fermentation efficiency of 83.26%, ethanol yield of 0.44 g/g, and the lowest residual sugar content of 6.50 g/L were achieved at 0.0037 H(-1) in the fermentation of 22°Bx molasses, indicating that the immobilization of cells using PVA, sugarcane pieces, and cotton towel is feasible and the established continuous system performs well.

Enhanced poly(γ-glutamic acid) fermentation by Bacillus subtilis NX-2 immobilized in an aerobic plant fibrous-bed bioreactor

To enhance poly(γ-glutamic acid) (PGA) production, a novel aerobic plant fibrous-bed bioreactor (APFB) was constructed for immobilized fermentation. Based on the analysis of the kinetics of immobilized-cell fermentation using the APFB and conventional free-cell fermentation, immobilized-cell fermentation exhibited more efficient PGA production. Furthermore, repeated fed-batch cultures for PGA production were conducted to evaluate the stability of the APFB system. Average final PGA concentration and productivity of 71.21±0.83g/L and 1.246±0.008g/L/h were respectively achieved by cells immobilized in bagasse during APFB, which was reused eight times over a period of 457±18h. Analysis of the membrane phospholipids and the key enzyme activities indicated that APFB-adapted cells had better productivity than original cells. Thus, this study demonstrated the significant potential of the APFB culture system in future industrial applications.

Radiation induces acid tolerance of Clostridium tyrobutyricum and enhances bioproduction of butyric acid through a metabolic switch

BACKGROUND

Butyric acid as a renewable resource has become an increasingly attractive alternative to petroleum-based fuels. Clostridium tyrobutyricum ATCC 25755T is well documented as a fermentation strain for the production of acids. However, it has been reported that butyrate inhibits its growth, and the accumulation of acetate also inhibits biomass synthesis, making production of butyric acid from conventional fermentation processes economically challenging. The present study aimed to identify whether irradiation of C. tyrobutyricum cells makes them more tolerant to butyric acid inhibition and increases the production of butyrate compared with wild type.

RESULTS

In this work, the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 3.6, 7.2 and 10.8 g·L-1 equivalents were studied. The results showed that, regardless of the irradiation used, there was a gradual inhibition of cell growth at butyric acid concentrations above 10.8 g·L-1, with no growth observed at butyric acid concentrations above 3.6 g·L-1 for the wild-type strain during the first 54 h of fermentation. The sodium dodecyl sulfate polyacrylamide gel electrophoresis also showed significantly different expression levels of proteins with molecular mass around the wild-type and irradiated strains. The results showed that the proportion of proteins with molecular weights of 85 and 106 kDa was much higher for the irradiated strains. The specific growth rate decreased by 50% (from 0.42 to 0.21 h-1) and the final concentration of butyrate increased by 68% (from 22.7 to 33.4 g·L-1) for the strain irradiated at 114 AMeV and 40 Gy compared with the wild-type strains.

CONCLUSIONS

This study demonstrates that butyric acid production from glucose can be significantly improved and enhanced by using 12C6+ heavy ion-irradiated C. tyrobutyricum. The approach is economical, making it competitive compared with similar fermentation processes. It may prove useful as a first step in a combined method employing long-term continuous fermentation of acid-production processes.

Cost-effective lignocellulolytic enzyme production by Trichoderma reesei on a cane molasses medium

BACKGROUND

Cane molasses, an important residue of the sugar industry, have the potential as a cost-effective carbon source that could serve as nutrients for industrial enzyme-producing microorganisms, especially filamentous fungi. However, the enzyme mixtures produced in such a complex medium are poorly characterized. In this study, the secretome of Trichoderma reesei grown on a cane molasses medium (CMM) as well as on a lactose-based conventional medium (LCM) were compared and analyzed by using proteomics.

RESULTS

In this study we show that both the CMM and LCM can serve as excellent growth media for T. reesei. The enzyme expression patterns in the two media were similar and a considerable number of the identified proteins on two-dimensional gel electrophoresis (2-DE) gels were those involved in biomass degradation. The most abundant cellulolytic enzymes identified in both media were cellobiohydrolases (Cel7A/Cel6A) and endoglucanases (Cel7A/Cel5A) and were found to be more abundant in CMM. We also found that both media can serve as an inducer of xylanolytic enzymes. The main xylanases (XYNI/XYNIV) and xyloglucanase (Cel74A) were found at higher concentrations in the CMM than LCM.

CONCLUSIONS

We analyzed the prevalent proteins secreted by T. reesei in the CMM and LCM. Here, we show that hydrolytic enzymes are cost-effective and can be produced on cane molasses as a carbon source which can be used to digest lignocellulolytic biomass.

Butyric acid from anaerobic fermentation of lignocellulosic biomass hydrolysates by Clostridium tyrobutyricum strain RPT-4213

A novel Clostridium tyrobutyricum strain RPT-4213 was found producing butyrate under strict anaerobic conditions. This strain produced 9.47 g L(-1) butyric acid from MRS media (0.48 g/g glucose). RPT-4213 was also used to ferment dilute acid pretreated hydrolysates including wheat straw (WSH), corn fiber (CFH), corn stover (CSH), rice hull (RHH), and switchgrass (SGH). Results indicated that 50% WSH with a Clostridia medium (Ct) produced the most butyric acid (8.06 g L(-1), 0.46 g/g glucose), followed by 50% SGH with Ct (6.01 g L(-1), 0.44 g/g glucose), however, 50% CSH Ct showed growth inhibition. RPT-4213 was then used in pH-controlled bioreactor fermentations using 60% WSH and SGH, with a dilute (0.5×) Ct medium, resulting 9.87 g L(-1) butyric acid in WSH (yield 0.44 g/g) and 7.05 g L(-1) butyric acid in SGH (yield 0.42 g/g). The titer and productivity could be improved through process engineering.

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.

Acetone, butanol, and ethanol production from cane molasses using Clostridium beijerinckii mutant obtained by combined low-energy ion beam implantation and N-methyl-N-nitro-N-nitrosoguanidine induction

In order to obtain mutant strains showing higher solvent tolerance and butanol production than those of wild-type strains, the butanol-producing strain Clostridium beijerinckii L175 was subjected to mutagenesis using a combined method of low-energy ion beam implantation and N-methyl-N-nitro-N-nitrosoguanidine induction. With this effort, mutant strain MUT3 was isolated. When it was used for butanol fermentation in P2 medium, the production of butanol was 15.8±0.7 g/L 46% higher than the wild-type strain. Furthermore, after optimization of butanol production from cane molasses with MUT3, the maximum butanol production of 14.9±0.5 g/L were obtained in crew-capped bottles. When ABE production by MUT3 was carried out in a bioreactor, the production of butanol and total solvent were 15.1±0.8 g/L and 22.1±0.9 g/L, respectively. The remarkable butanol production and solvent tolerance of MUT3 make it promising for butanol production from cane molasses.

Genome Sequence of Clostridium tyrobutyricum ATCC 25755, a Butyric Acid-Overproducing Strain

Clostridium tyrobutyricum ATCC 25755 is an efficient producer of butyric acid. Here we report a 3.01-Mb assembly of its genome sequence and other useful information, including the coding sequences (CDSs) responsible for an alternative pathway leading to acetate synthesis as well as a series of membrane transport systems.

Butyric acid production from sugarcane bagasse hydrolysate by Clostridium tyrobutyricum immobilized in a fibrous-bed bioreactor

A fermentation process using Clostridium tyrobutyricum immobilized in a fibrous-bed bioreactor (FBB) was developed for butyric acid production from sugarcane bagasse (SCB) hydrolysate. SCB was first treated with dilute acid and then hydrolyzed with cellulases. The hydrolysate containing glucose and xylose was used as carbon source for the fermentation without detoxification. The bacterium was able to grow at a specific growth rate of ∼0.06 h(-1) in media containing 15-20% (w/v) SCB in serum bottles. In batch cultures in the FBB, both glucose and xylose in the SCB hydrolysate were simultaneously converted to butyrate with a high yield (0.45-0.54 g/gsugar) and productivity (0.48-0.60 g/Lh). A final butyrate concentration of 20.9 g/L was obtained in a fed-batch culture, with an overall productivity of 0.51 g/Lh and butyrate yield of 0.48 g/g sugar consumed. This work demonstrated the feasibility of using SCB as a low-cost feedstock to produce butyric acid.

Economical production of poly(γ-glutamic acid) using untreated cane molasses and monosodium glutamate waste liquor by Bacillus subtilis NX-2

The production of poly(γ-glutamic acid) by Bacillus subtilis NX-2 from cane molasses and monosodium glutamate waste liquor (MGWL) was studied for the first time in this work. When batch fermentation was carried out with untreated molasses, 33.6±0.37 g L(-1) PGA was obtained with a productivity of 0.46±0.006 g L(-1) h(-1). In order to minimize the substrate inhibition, fed-batch fermentation was performed with untreated or hydrolyzed molasses in 7.5 L bioreactor, giving 50.2±0.53 and 51.1±0.51 g L(-1) of PGA at 96 h, respectively. Further studies were carried out by using MGWL as another carbon source, resulting in a PGA concentration of 52.1±0.52 g L(-1) with a productivity of 0.54±0.003 g L(-1) h(-1). These results suggest that the low-cost cane molasses and MGWL can be used for the environmental-friendly and economical production of PGA by B. subtilis NX-2.

Improving the productivity of propionic acid with FBB-immobilized cells of an adapted acid-tolerant Propionibacterium acidipropionici

Propionic acid is an important short-chain fatty acid with many applications, but its large-scale bioproduction was hindered by the low productivity. An adapted acid-tolerant Propionibacterium acidipropionici CGMCC 1.2230 strain was selected to produce propionic acid with a relatively high productivity (0.29 g/(Lh)) in the free-cell fermentation. Further immobilized-cell fermentation in fibrous-bed bioreactor (FBB) supported high-level repeated batch fermentations with a high productivity of 0.96 g/(Lh). The FBB also presents the potential to increase final propionic acid concentration by using glucose feeding strategy. The propionic acid concentration was increased to 51.2g/L in the fed-batch fermentation with the productivity of 0.71 g/(Lh). By adopting the above strategies, sugarcane bagasse hydrolysate could support the production of propionic acid with high productivity in the repeat-batch and fed-batch fermentations. The present work would pave one road to the accomplishment of large-scale bioproduction of propionic acid from renewable resources.

Molasses-based growth and production of oil and astaxanthin by Chlorella zofingiensis

The aim of this study is to evaluate the industrial waste cane molasses as a carbon source for cell growth, lipid and astaxanthin production of Chlorella zofingiensis. Pretreated with cation exchange resin to remove the metal ions, cane molasses provided better productivities of biomass, lipid, and astaxanthin (1.55, 0.71 g L(-1)day(-1) and 1.7 mg L(-1)day(-1), respectively) than glucose. Using a strategy of semi-continuous cultures coupled with feeding at a low concentration, molasses without pretreatment has the same effect as pretreated one on supporting the algal cell growth, lipid and astaxanthin production. The efficient metabolism of molasses triggered the up-regulation of genes involved in fatty acid and also astaxanthin biosynthesis, leading to the very high production of the two metabolites. This study highlights the possibility of using C. zofingiensis to deal with industrial wastes and to produce profitable biodiesel as well as the high-value astaxanthin.

Adaptive evolution for fast growth on glucose and the effects on the regulation of glucose transport system in Clostridium tyrobutyricum

Laboratory adaptive evolution of microorganisms offers the possibility of relating acquired mutations to increased fitness of the organism under the conditions used. By combining a fibrous-bed bioreactor, we successfully developed a simple and valuable adaptive evolution strategy in repeated-batch fermentation mode with high initial substrate concentration and evolved Clostridium tyrobutyricum mutant with significantly improved butyric acid volumetric productivity up to 2.25 g/(L h), which is the highest value in batch fermentation reported so far. Further experiments were conducted to pay attention to glucose transport system in consideration of the high glucose consumption rate resulted from evolution. Complete characterization and comparison of the glucose phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) were carried out in the form of toluene-treated cells and cell-free extracts derived from both C. tyrobutyricum wide-type and mutant, while an alternative glucose transport route that requires glucokinase was confirmed by the phenomena of resistance to the glucose analogue 2-deoxyglucose and ATP-dependent glucose phosphorylation. Our results suggest that C. tyrobutyricum mutant is defective in PTS activity and compensates for this defect with enhanced glucokinase activity, resulting in the efficient uptake and consumption of glucose during the whole metabolism.