Co-fermentation Of Glucose Research Articles

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.

Data for rapid ethanol production at elevated temperatures by engineered thermotolerant Kluyveromyces marxianus via the NADP(H)-preferring xylose reductase-xylitol dehydrogenase pathway.

A thermo-tolerant NADP(H)-preferring xylose pathway was constructed in Kluyveromyces marxianus for ethanol production with xylose at elevated temperatures (Zhang et al., 2015 [25]). Ethanol production yield and efficiency was enhanced by pathway engineering in the engineered strains. The constructed strain, YZJ088, has the ability to co-ferment glucose and xylose for ethanol and xylitol production, which is a critical step toward enabling economic biofuel production from lignocellulosic biomass. This study contains the fermentation results of strains using the metabolic pathway engineering procedure. The ethanol-producing abilities of various yeast strains under various conditions were compared, and strain YZJ088 showed the highest production and fastest productivity at elevated temperatures. The YZJ088 xylose fermentation results indicate that it fermented well with xylose at either low or high inoculum size. When fermented with an initial cell concentration of OD600=15 at 37 °C, YZJ088 consumed 200 g/L xylose and produced 60.07 g/L ethanol; when the initial cell concentration was OD600=1 at 37 °C, YZJ088 consumed 98.96 g/L xylose and produced 33.55 g/L ethanol with a productivity of 0.47 g/L/h. When fermented with 100 g/L xylose at 42 °C, YZJ088 produced 30.99 g/L ethanol with a productivity of 0.65 g/L/h, which was higher than that produced at 37 °C.

High-cell-density cultivation of an engineered Rhodococcus opacus strain for lipid production via co-fermentation of glucose and xylose

An engineered strain MITXM-61 of Rhodococcus opacus PD630 capable of utilizing xylose was used to produce biofuel precursor-triacylglycerols (TAG) from mixed glucose–xylose substrates. Optimal nitrogen source and carbon source concentrations were investigated for cell growth and microbial lipid production by MITXM-61 in flask cultures. In a two-stage batch culture, the maximum lipid yield (0.152gTAGperg consumed carbon source) was achieved by utilizing a mixture of glucose and xylose. The fed-batch culture featured intermittent feeding of refined xylose solution during the lipid accumulation stage provided 45gL−1 of cell dry weight, 54% (gTAGperg cell dry weight) of lipid content, 0.179gg−1 (gTAGperg consumed carbon source) of lipid yield, and a 6.9gL−1day−1 of lipid productivity. Fatty acids extracted from microbial lipids produced by MITXM-61 were predominately palmitic and oleic acids, which are the major components in TAG-derived biofuels.

Substrate consumption and hydrogen production via co-fermentation of monomers derived from carbohydrates and proteins in biomass wastes

Fermentative hydrogen production from biomass wastes is a promising technology combining waste treatment and clean fuel production. Biomass wastes have various types and components, while the fundamental fermentation reactions involve monosaccharides and amino acids. In this study, typical monosaccharides (glucose and xylose) and amino acids (glutamic acid, aspartic acid, serine, glycine, arginine and alanine) were mixed and fermented by anaerobic fermentative bacteria (AFB) obtained from heat pre-treated anaerobic digestion sludge, to directly examine the substrate consumption and hydrogen production during the co-fermentation of monosaccharides and amino acids. Hydrogen was mainly produced from the fermentation of monosaccharides, but not from the fermentation of amino acids. Monosaccharide consumption generally preceded amino acid consumption. Glucose was more readily utilised by AFB than xylose. The maximum volumetric hydrogen productivity and production rate from the co-fermentation of glucose and mixed amino acids was 2.7 times and 3.1 times higher than those from the co-fermentation of xylose and mixed amino acids. Glutamic acid, serine and alanine were more readily utilised by AFB than aspartic acid, glycine and arginine. The co-fermentation of monosaccharides and amino acids showed efficient energy conversion and carbon conversion, with the maximum efficiencies of 83.3% and 93.3%, respectively.

Co-fermentation of glucose, starch, and cellulose for mesophilic biohydrogen production

The aim of this study was to assess the synergistic effects of co-fermentation of glucose, starch, and cellulose using anaerobic digester sludge (ADS) on the biohydrogen (H2) production and the associated microbial communities. Yields of H2 were 1.22, 1.00, and 0.15 mol H2/mol hexose-added in fermentation reactions containing glucose, starch, and cellulose as mono-substrates. The H2 yields were greater by an average of 27 ± 4% than expected in all the different co-substrate conditions, which affirmed that co-fermentation of different substrates improved the H2 potential. Glucose addition to starch and/or cellulose favored acetate synthesis, while cellulose degradation was associated with the propionate synthesis pathway. Illumina sequencing technology and bioinformatics analyses revealed operational taxonomic units (OTUs) in the Phyla Bacteroides, Chloroflexi, Firmicutes, Proteobacteria, Spirochaetes, Synergistes, and Thermotogae were common in mono- and co-substrate batches. However, OTUs in the Phyla Acidobacteria, Actinobacteria, and Bacteroidetesee were unique to only the co-substrate conditions.

Cofermentation of glucose and galactose by a newly isolated Saccharomyces cerevisiae strain in free and immobilized forms

A newly isolated yeast strain from the soil of grape fruit farm was identified as Saccharomyces cerevisiae Wu-Y2 through molecular characterization. This strain, whether used in free or immobilized form, showed a good performance on co-fermentation of reagent grade mixed sugars comprising of glucose and galactose in production of bioethanol in batch and fed batch culture. The yield coefficient (YE/S; 0.47g/g) for ethanol from monosaccharide and yield efficiency (YE; 92.0%) after 48h fermentation of mixed sugars shown by this wild-type S. cerevisiae Wu-Y2 were much higher than those by engineered S. cerevisiae (D452-2BT) strain (0.34g/g, 67%) and engineered industrial distillers’ yeast (0.28g/g and 55%). The immobilized S. cerevisiae Wu-Y2 cells exhibited a high degree of operational stability for several weeks without significant loss of viability or ethanologenicity in fed batch culture and it can tolerate up to 7–10% of ethanol for more than a month. This strain also showed good ability to utilize glucose and galactose present in red seaweed hydrolysate with high ethanol conversion efficiency; it showed significant potential to be an efficient bioethanol producer using seaweed as a feedstock.

Effect of fermentation conditions on the flocculation of recombinant Saccharomyces cerevisiae capable of co-fermenting glucose and xylose.

Flocculation is a desirable property in industrial yeasts and is particularly important in the fuel ethanol industry because it provides a simple and cost-free way to separate yeast cells from fermentation products. In the present study, the effect of pH and lignocellulose-derived sugars on yeast flocculation was investigated using a flocculent Saccharomyces cerevisiae, MA-R4, which has been recombinantly engineered to simultaneously co-ferment glucose and xylose to ethanol with high productivity. The flocculation level of MA-R4 dramatically decreased at pH values below 3.0 during co-fermentation of glucose and xylose. Sedimentation and microscopic observation revealed that flocculation was induced in MA-R4 when it fermented glucose, a glucose/xylose mixture, or mannose, whereas attempts to ferment xylose, galactose, and arabinose led to the loss of flocculation. MA-R4 fermented xylose and galactose more slowly than glucose and mannose. Therefore, the various flocculation behaviors shown by MA-R4 should be useful in the control of ethanol fermentation processes.

Simultaneous saccharification and co-fermentation of aqueous ammonia pretreated corn stover with an engineered Saccharomyces cerevisiae SyBE005

Co-fermentation of glucose and xylose from lignocelluloses is an efficient approach to increasing ethanol production. Simultaneous saccharification and co-fermentation (SSCF) of corn stover pretreated with aqueous ammonia was performed using engineered yeast with xylose utilization pathway. Thus far, the effect of the several key factors on SSCF was investigated, including temperature, inoculation size, pre-hydrolysis and pH. Ethanol concentration was achieved to 36.5g/L during SSCF process with 6% glucan loading. The addition of Tween 20 reduced enzyme loading, i.e., from 15 to 7.5FPU/gglucan with the same final ethanol concentration. The ethanol concentration was achieved to 70.1g/L at 12% glucan loading. Yeast feeding, combined with substrate and enzyme feeding, was proved to be an efficient approach for SSCF with high solid loading.

Evaluation of Paecilomyces variotii potential in bioethanol production from lignocellulose through consolidated bioprocessing.

The ascomycete Paecillomyces variotii was evaluated for the first time as a candidate species for the production of bioethanol from lignocellulose through consolidated bioprocessing (CBP) approaches. The examined strain (ATHUM 8891) revealed all the necessary phenotypic characteristics required for 2nd generation biofuel production. The fungus is able to efficiently ferment glucose and xylose to ethanol, with yields close to the theoretical maximum. Nitrogen supplementation greatly affected ethanol production with nitrate-nitrogen presenting the best results. Notably, ethanol yield on xylose fermentation was higher than that of glucose, while in co-fermentation of glucose-xylose mixtures no distinguished diauxic behavior was observed. Furthermore, the fungus seems to possess the necessary enzyme factory for the degradation of lignocellulosic biomass, as it was able to grow and produce ethanol on common agro-industrial derivatives. Overall, the results of our study indicate that P. variotii is a new and possibly powerful candidate for CBP applications.

Biosynthesis of 1,3-propanediol from glycerol with Lactobacillus reuteri: Effect of operating variables

Chemical synthesis of 1,3-propanediol (1,3-PD) is environmentally unfriendly and hence its microbial production is preferred, especially for biomedical, cosmetic and textile applications. In this work, production of 1,3-PD by co-fermentation of glucose and glycerol by Lactobacillus reuteri was investigated under different cultivation conditions such as aeration, acetate concentration and different molar ratios of glucose/glycerol. The final concentration of 1,3-PD and yield attained under unaerated conditions was close to that obtained under anaerobic conditions. Addition of acetate in the initial medium at 5 g/l increased the productivity of 1,3-PD but above this concentration it was found to be inhibitory. Batch reactor experiments showed that the molar ratio of glucose and glycerol in the medium affected the fermentation pattern. The effect of molar ratios was further investigated in fed-batch fermentation and the optimum ratio was found to be 1.5. In repeated fed-batch fermentation with co-feeding of glucose and glycerol in the molar ratio of 1.5, 1,3-PD concentration reached up to 65.3 g/l, which is the highest 1,3-PD concentration reported so far for this strain. The yield (0.97 mol/mol) based on glycerol utilized also approached the theoretical value (1 mol/mol).

Metabolic engineering of a Saccharomyces cerevisiae strain capable of simultaneously utilizing glucose and galactose to produce enantiopure (2R,3R)-butanediol

2,3-Butanediol (BDO) is an important chemical with broad industrial applications and can be naturally produced by many bacteria at high levels. However, the pathogenicity of these native producers is a major obstacle for large scale production. Here we report the engineering of an industrially friendly host, Saccharomyces cerevisiae, to produce BDO at high titer and yield. By inactivation of pyruvate decarboxylases (PDCs) followed by overexpression of MTH1 and adaptive evolution, the resultant yeast grew on glucose as the sole carbon source with ethanol production completely eliminated. Moreover, the pdc- strain consumed glucose and galactose simultaneously, which to our knowledge is unprecedented in S. cerevisiae strains. Subsequent introduction of a BDO biosynthetic pathway consisting of the cytosolic acetolactate synthase (cytoILV2), Bacillus subtilis acetolactate decarboxylase (BsAlsD), and the endogenous butanediol dehydrogenase (BDH1) resulted in the production of enantiopure (2R,3R)-butanediol (R-BDO). In shake flask fermentation, a yield over 70% of the theoretical value was achieved. Using fed-batch fermentation, more than 100g/L R-BDO (1100mM) was synthesized from a mixture of glucose and galactose, two major carbohydrate components in red algae. The high titer and yield of the enantiopure R-BDO produced as well as the ability to co-ferment glucose and galactose make our engineered yeast strain a superior host for cost-effective production of bio-based BDO from renewable resources.

Enhanced xylose fermentation capacity related to an altered glucose sensing and repression network in a recombinant Saccharomyces cerevisiae

The co-fermentation of glucose and xylose is one of the issues in decreasing the price of biofuel or chemicals produced from lignocellulosic materials. A glucose and xylose co-utilizing Saccharomyces cerevisiae was obtained through rational genetic manipulation. Non-rational evolution in xylose was performed, and the xylose utilization efficiency of the engineered strain was significantly enhanced. The results of transcriptome study suggested that Snf1/Mig1-mediated regulation, a part of glucose sensing and repression network, was altered in the evolved strain and might be related to the enhancement of xylose utilization.

Direct ethanol production from glucose, xylose and sugarcane bagasse by the corn endophytic fungi Fusarium verticillioides and Acremonium zeae

Production of ethanol with two corn endophytic fungi, Fusarium verticillioides and Acremonium zeae, was studied. The yield of ethanol from glucose, xylose and a mixture of both sugars were 0.47, 0.46 and 0.50g/g ethanol/sugar for F. verticillioides and 0.37, 0.39 and 0.48g/g ethanol/sugar for A. zeae. Both fungi were able to co-ferment glucose and xylose. Ethanol production from 40g/L of pre-treated sugarcane bagasse was 4.6 and 3.9g/L for F. verticillioides and A. zeae, respectively, yielding 0.31g/g of ethanol per consumed sugar. Both fungi studied were capable of co-fermenting glucose and xylose at high yields. Moreover, they were able to produce ethanol directly from lignocellulosic biomass, demonstrating to be suitable microorganisms for consolidated bioprocessing.

Simultaneous saccharification and co-fermentation of whole wheat in integrated ethanol production

Two of the most important ways of reducing the production cost of lignocellulosic ethanol are to increase the ethanol yield and the concentration in the fermentation broth. This can be facilitated by co-fermentation of glucose and xylose from agricultural residues such as wheat straw, due to the high amount of xylose in the hemicelluloses in these materials.Simultaneous saccharification and co-fermentation (SSCF) of steam-pretreated wheat straw (SPWS) with and without the addition of liquefied wheat meal (LWM) was performed using the pentose-fermenting yeast, TMB3400. The highest overall ethanol yield in batch operation, of around 70%, equivalent to an ethanol concentration of 43.7 g L−1, was achieved using SPWS with 7.5% water-insoluble solids (WIS) and addition of LWM with 1% WIS. Using SPWS with a higher WIS (10%) resulted in a decreased yield, 60%, although the concentration of ethanol increased to 53.0 g L−1. SSCF of 7.5% straw was also performed with a single (after 20 h) or fed-batch addition of 1% WIS LWM (after 20, 24 and 28 h) resulting in an increase in both ethanol yield and concentration compared to the reference, without wheat meal addition, but no significant difference compared to the batch experiments.The addition of wheat meal to SSCF did not improve xylose utilization significantly, probably due to the instant release of glucose from the liquefied meal, which hampers the uptake of xylose. The instant release of glucose was shown to be caused by the high amylase activity of the β-glucosidase enzyme preparation.

Simultaneous hydrogen and ethanol production from a mixture of glucose and xylose using extreme thermophiles I: Effect of substrate and pH

The simultaneous hydrogen and ethanol production from glucose and xylose was investigated. The effect of carbon sources on hydrogen and ethanol production was examined in batches. When the substrate concentration was increased from 1 g/L to 7 g/L, the hydrogen yield decreased from 0.74 mol/mol to 0.15 mol/mol and from 0.67 mol/mol to 0.07 mol/mol for glucose and xylose. The highest ethanol yield of 1.19 mol/(mol·glucose) was obtained at 5 g/L glucose and 6 g/L xylose concentrations. For the co-fermentation of glucose and xylose, the highest ethanol yield 1.54 mol/(mol·hexose) was obtained at 2.5 g/L glucose to 2.5 g/L xylose (1:1). However, the hydrogen yield was not significantly affected by the glucose to xylose ratio. Continuous co-fermentation of glucose and xylose by extreme thermophiles was successfully demonstrated using an upflow anaerobic reactor. The hydrogen production rate, the ethanol concentration, and the substrate degradation efficiency increased along with pH. The optimal pH for the continuous mode was determined to be in the range of 5.8–6.6.

Effect of salts on the Co-fermentation of glucose and xylose by a genetically engineered strain of Saccharomyces cerevisiae

BackgroundA challenge currently facing the cellulosic biofuel industry is the efficient fermentation of both C5 and C6 sugars in the presence of inhibitors. To overcome this challenge, microorganisms that are capable of mixed-sugar fermentation need to be further developed for increased inhibitor tolerance. However, this requires an understanding of the physiological impact of inhibitors on the microorganism. This paper investigates the effect of salts on Saccharomyces cerevisiae 424A(LNH-ST), a yeast strain capable of effectively co-fermenting glucose and xylose.ResultsIn this study, we show that salts can be significant inhibitors of S. cerevisiae. All 6 pairs of anions (chloride and sulfate) and cations (sodium, potassium, and ammonium) tested resulted in reduced cell growth rate, glucose consumption rate, and ethanol production rate. In addition, the data showed that the xylose consumption is more strongly affected by salts than glucose consumption at all concentrations. At a NaCl concentration of 0.5M, the xylose consumption rate was reduced by 64.5% compared to the control. A metabolomics study found a shift in metabolism to increased glycerol production during xylose fermentation when salt was present, which was confirmed by an increase in extracellular glycerol titers by 4 fold. There were significant differences between the different cations. The salts with potassium cations were the least inhibitory. Surprisingly, although salts of sulfate produced twice the concentration of cations as compared to salts of chloride, the degree of inhibition was the same with one exception. Potassium salts of sulfate were less inhibitory than potassium paired with chloride, suggesting that chloride is more inhibitory than sulfate.ConclusionsWhen developing microorganisms and processes for cellulosic ethanol production, it is important to consider salt concentrations as it has a significant negative impact on yeast performance, especially with regards to xylose fermentation.

Improved efficiency of butanol production by absorbed lignocellulose fermentation

Alkali-treated steam-exploded corn stover (SECSAT) was used as solid substrate for acetone-butanol-ethanol (ABE) production by absorbed lignocellulose fermentation (ALF) using Clostridium acetobutylicum ATCC 824. The ABE concentration in ALF culture had increased by 47% compared with that in submerged culture. More surprisingly, the acetone production was promoted and ethanol production was lower in the presence of SECSAT than that in its absence. ALF was also successfully in cofermentation of glucose and xylose, although decreased fermentability with an increase in the proportion of xylose. An invariable chemical composition and dry weight of SECSAT was found in ALF. Partial simultaneous saccharification and fermentation of SECSAT using a certain amount of cellulase could not only enhance the ABE concentration by 71%, but also significantly increase the area proportion of fiber cells in SECSAT from 53% to 90%, which would be an excellent paper making material.

Characterization of a Recombinant Flocculent Saccharomyces cerevisiae Strain That Co-Ferments Glucose and Xylose: II. Influence of pH and Acetic Acid on Ethanol Production

The inhibitory effects of pH and acetic acid on the co-fermentation of glucose and xylose in complex medium by recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated. In the absence of acetic acid, the fermentation performance of strain MA-R4 was similar between pH 4.0-6.0, but was negatively affected at pH 2.5. The addition of acetic acid to batch cultures resulted in negligible inhibition of several fermentation parameters at pH 6.0, whereas the interactive inhibition of pH and acetic acid on the maximum cell and ethanol concentrations, and rates of sugar consumption and ethanol production were observed at pH levels below 5.4. The inhibitory effect of acetic acid was particularly marked for the consumption rate of xylose, as compared with that of glucose. With increasing initial acetic acid concentration, the ethanol yield slightly increased at pH 5.4 and 6.0, but decreased at pH values lower than 4.7. Notably, ethanol production was nearly completely inhibited under low pH (4.0) and high acetic acid (150-200mM) conditions. Together, these results indicate that the inhibitory effects of acetic acid and pH on ethanol fermentation by MA-R4 are highly synergistic, although the inhibition can be reduced by increasing the medium pH.

Cofermentation of Glucose, Xylose, and Cellobiose by the Beetle-Associated Yeast Spathaspora passalidarum

Fermentation of cellulosic and hemicellulosic sugars from biomass could resolve food-versus-fuel conflicts inherent in the bioconversion of grains. However, the inability to coferment glucose and xylose is a major challenge to the economical use of lignocellulose as a feedstock. Simultaneous cofermentation of glucose, xylose, and cellobiose is problematic for most microbes because glucose represses utilization of the other saccharides. Surprisingly, the ascomycetous, beetle-associated yeast Spathaspora passalidarum, which ferments xylose and cellobiose natively, can also coferment these two sugars in the presence of 30 g/liter glucose. S. passalidarum simultaneously assimilates glucose and xylose aerobically, it simultaneously coferments glucose, cellobiose, and xylose with an ethanol yield of 0.42 g/g, and it has a specific ethanol production rate on xylose more than 3 times that of the corresponding rate on glucose. Moreover, an adapted strain of S. passalidarum produced 39 g/liter ethanol with a yield of 0.37 g/g sugars from a hardwood hydrolysate. Metabolome analysis of S. passalidarum before onset and during the fermentations of glucose and xylose showed that the flux of glycolytic intermediates is significantly higher on xylose than on glucose. The high affinity of its xylose reductase activities for NADH and xylose combined with allosteric activation of glycolysis probably accounts in part for its unusual capacities. These features make S. passalidarum very attractive for studying regulatory mechanisms enabling bioconversion of lignocellulosic materials by yeasts.

Separate hydrolysis and co-fermentation for improved xylose utilization in integrated ethanol production from wheat meal and wheat straw

BackgroundThe commercialization of second-generation bioethanol has not been realized due to several factors, including poor biomass utilization and high production cost. It is generally accepted that the most important parameters in reducing the production cost are the ethanol yield and the ethanol concentration in the fermentation broth. Agricultural residues contain large amounts of hemicellulose, and the utilization of xylose is thus a plausible way to improve the concentration and yield of ethanol during fermentation. Most naturally occurring ethanol-fermenting microorganisms do not utilize xylose, but a genetically modified yeast strain, TMB3400, has the ability to co-ferment glucose and xylose. However, the xylose uptake rate is only enhanced when the glucose concentration is low.ResultsSeparate hydrolysis and co-fermentation of steam-pretreated wheat straw (SPWS) combined with wheat-starch hydrolysate feed was performed in two separate processes. The average yield of ethanol and the xylose consumption reached 86% and 69%, respectively, when the hydrolysate of the enzymatically hydrolyzed (18.5% WIS) unwashed SPWS solid fraction and wheat-starch hydrolysate were fed to the fermentor after 1 h of fermentation of the SPWS liquid fraction. In the other configuration, fermentation of the SPWS hydrolysate (7.0% WIS), resulted in an average ethanol yield of 93% from fermentation based on glucose and xylose and complete xylose consumption when wheat-starch hydrolysate was included in the feed. Increased initial cell density in the fermentation (from 5 to 20 g/L) did not increase the ethanol yield, but improved and accelerated xylose consumption in both cases.ConclusionsHigher ethanol yield has been achieved in co-fermentation of xylose and glucose in SPWS hydrolysate when wheat-starch hydrolysate was used as feed, then in co-fermentation of the liquid fraction of SPWS fed with the mixed hydrolysates. Integration of first-generation and second-generation processes also increases the ethanol concentration, resulting in a reduction in the cost of the distillation step, thus improving the process economics.