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At least 613 records · Page 34Linked to original sources
PubMed2003

Glycerol formation during wine fermentation is mainly linked to Gpd1p and is only partially controlled by the HOG pathway.

Glycerol 3-phosphate dehydrogenase, a key enzyme in the production of glycerol, is encoded by GPD1 and GPD2. The isoforms encoded by these genes have different functions, in osmoregulation and redox balance, respectively. We investigated the roles of GPD1, GPD2 and HOG1-the kinase involved in the response to osmotic stress-in glycerol production during wine fermentation. We found that the deletion of GPD2 in a wine yeast-derived strain did not affect growth or fermentation performance and reduced glycerol production by only 20%. In contrast, a gpd1delta mutant displayed a prolonged lag phase, and produced 40% less glycerol than the wild-type strain. The deletion of HOG1 resulted in a slight decrease in growth rate and a 20% decrease in glycerol production, indicating that the HOG pathway operates under wine fermentation conditions. However, the hog1delta mutant was not as severely affected as the gpd1delta mutant during the first few hours of fermentation, and continued to express GPD1 strongly. The hog1delta mutant was able to increase glycerol production in response to high sugar concentration (15-28% glucose), to almost the same extent as the wild-type, whereas this response was totally abolished in the gpd1delta mutant. These data show that Gpd1p plays a major role in glycerol formation, particularly during the first few hours of exposure to high sugar concentration, and that GPD2 is only of little significance in anaerobic fermentation by wine yeast. The results also demonstrate that the HOG pathway exerts only limited control over GPD1 expression and glycerol production during wine fermentation.

Blotting, Northern↗
PubMed2004

A multi-scale study of industrial fermentation processes and their optimization.

In this article problems in multi-scale industrial fermentation processes are discussed. The problems are generated virtually, by using computer simulation on three different scales--the molecular scale (genetics), the cellular scale (metabolic regulation), and the reactor engineering scale. Inter-scale observation and operation are deemed to be crucial in the optimization of bioprocesses. Bioreaction engineering based on metabolic flux analysis and control is further elucidated. Optimization methodology for study of multi-scale problems in a fermentation process, based on correlation of data, and the scale-up technique for regulation of several bioprocess parameters are generalized by investigation of two typical fermentation processes. A novel bioreactor system was designed to monitor mass flux (for example substrates and (by-)products) in a fermentation process. It was successfully applied to the optimization and scale-up of an industrial fermentation process for penicillin, erythromycin, chlortetracyclin, inosine, and guanosine, and for production of recombinant human serum albumin and a malaria vaccine by use of the Pichia expression system. Substantial improvement of industrial fermentation productivity was achieved.

Bioreactors↗
PubMed1996

Levels of antinutritional factors in pearl millet as affected by processing treatments and various types of fermentation.

Pearl millet (Pennisetum typhoideum) was fermented with Lactobacilli or yeasts alone and in combination, and with natural microflora after various processing treatments, as grinding, soaking, debranning, dry heat treatment, autoclaving and germination. Fermentation was carried out at 30 degrees C for 48 hours with Lactobacillus plantarum (LP) and Rhodotorula (R) isolated from naturally fermented pearl millet and Lactobacillus acidophilus (LA), Candida utilis (CU) and natural microflora (NF). Germination and autoclaving, and debranning and autoclaving were the most effective processing treatments to reduce the phytic acid, amylase inhibitors and polyphenols. There was a further reduction in these antinutrients due to fermentation. Phytic acid and amylase inhibitors were completely eliminated after fermentation in some of the samples especially in soaked, debranned and germinated ones. Polyphenols were altered non-significantly in general but fermentation with Lp + R and NF caused a significant increase in polyphenols.

Fermentation↗
PubMed1982

Differential production of acid by Enterobacteriaceae in OF media and in fermentation broth.

Several species of Enterobacteriaceae were checked for acid formation from some carbohydrates or alcohols in OF medium [OF Basal Medium, Baltimore Biological Laboratories] and in a traditional "fermentation broth". After selection of those species that formed acid only oxidatively or fermentatively in OF, it was found that acid formation in the fermentation broth could reflect fermentation or oxidation, but that it was not necessarily related to either. In oxidative species, it occurred less frequently than oxidation in OF and was usually delayed. Fermentative species (in OF) either yielded acid in fermentation broth or did not, depending on the species. Thus, OF media cannot be substituted for traditional broths, although they may be of value in differentiating certain species.

Culture Media↗
PubMed2001

Anaerobic fermentation of gelatinized sago starch-derived sugars to acetone-1-butanol-ethanol solvent by Clostridium acetobutylicum.

A study of the kinetics and performance of solvent-yielding batch fermentation of individual sugars and their mixture derived from enzymic hydrolysis of sago starch by Clostridium acetobutylicum showed that the use of 30 g/L gelatinized sago starch as the sole carbon source produced 11.2 g/L total solvent, i.e. 1.5-2 times more than with pure maltose or glucose used as carbon sources. Enzymic pretreatment of gelatinized sago starch yielding maltose and glucose hydrolyzates prior to the fermentation did not improve solvent production as compared to direct fermentation of gelatinized sago starch. The solvent yield of direct gelatinized sago starch fermentation depended on the activity and stability of amylolytic enzymes produced during the fermentation. The pH optima for alpha-amylase and glucoamylase were found to be at 5.3 and 4.0-4.4, respectively. alpha-Amylase showed a broad pH stability profile, retaining more than 80% of its maximum activity at pH 3.0-8.0 after a 1-d incubation at 37 degrees C. Since C. acetobutylicum alpha-amylase has a high activity and stability at low pH, this strain can potentially be employed in a one-step direct solvent-yielding fermentation of sago starch. However, the C. acetobutylicum glucoamylase was only stable at pH 4-5, maintaining more than 90% of its maximum activity after a 1-d incubation at 37 degrees C.

1-Butanol↗
PubMed1997

Fermentation of biomass-derived glucuronic acid by pet expressing recombinants of E. coli B.

The economics of large-scale production of fuel ethanol from biomass and wastes requires the efficient utilization of all the sugars derived from the hydrolysis of the heteropolymeric hemicellulose component of lignocellulosic feedstocks. Glucuronic and 4-O-methyl-glucuronic acids are major side chains in xylans of the grasses and hardwoods that have been targeted as potential feedstocks for the production of cellulosic ethanol. The amount of these acids is similar to that of arabinose, which is now being viewed as another potential substrate in the production of biomass-derived ethanol. This study compared the end-product distribution associated with the fermentation of D-glucose (Glc) and D-glucuronic acid (GlcUA) (as sole carbon and energy sources) by Escherichia coli B (ATCC 11303) and two different ethanologenic recombinants--a strain in which pet expression was via a multicopy plasmid (pLOI297) and a chromosomally integrated construct, strain KO11. pH-stat batch fermentations were conducted using a modified LB medium with 2% (w/v) Glc or GlcUA with the set-point for pH control at either 6.3 or 7.0. The nontransformed host culture produced only lactic acid from glucose, but fermentation of GlcUA yielded a mixture of ethanol, acetic, and lactic acids, with acetic acid being the predominant end-product. The ethanol yield associated with GlcUA fermentation by both recombinants was similar, but acetic acid was a significant by-product. Increasing the pH from 6.3 to 7.0 increased the rate of glucuronate fermentation, but it also decreased the ethanol mass yield from 0.22 to 0.19 g/g primarily because of an increase in acetic acid production. In all fermentations there was good closure of the carbon mass balance, the exception being the recombinant bearing plasmid pLOI297 that produced an unidentified product from GlcUA. The metabolism of GlcUA by this metabolically engineered construct remains unresolved. The results offered insights into metabolic fluxes and the regulation of pyruvate catabolism in the wild-type and engineered strains. End-product distribution for metabolism of glucuronic acid by the nontransformed, wild-type E. coli B and recombinant strain KO11 suggests that the enzyme pyruvate-formate lyase is not solely responsible for the production of acetylCoA from pyruvate and that derepressed pyruvate dehydrogenase may play a significant role in the metabolism of GlcUA.

Acetyltransferases↗
PubMed2001

Significance of pantothenate for glucose fermentation by Oenococcus oeni and for suppression of the erythritol and acetate production.

The heterofermentative lactic acid bacterium Oenococcus oeni requires pantothenic acid for growth. In the presence of sufficient pantothenic acid, glucose was converted by heterolactic fermentation stoichiometrically to lactate, ethanol and CO2. Under pantothenic acid limitation, substantial amounts of erythritol, acetate and glycerol were produced by growing and resting bacteria. Production of erythritol and glycerol was required to compensate for the decreasing ethanol production and to enable the synthesis of acetate. In ribose fermentation, there were no shifts in the fermentation pattern in response to pantothenate supply. In the presence of pantothenate, growing O. oeni contained at least 10.2 microM HSCoA, whereas the HSCoA content was tenfold lower after growth in pantothenate-depleted media. HSCoA and acetyl-CoA are cosubstrates of phosphotransacetylase and acetaldehyde dehydrogenase from the ethanol pathway. Both enzymes were found with activities commensurate with their function in ethanol production during heterolactic fermentation. From the kinetic data of the enzymes and the HSCoA and acetyl-CoA contents, it can be calculated that, under pantothenate limitation, phosphotransacetylase, and in particular acetaldehyde dehydrogenase activities become limiting due to low levels of the cosubstrates. Thus HSCoA deficiency represents the major limiting factor in heterolactic fermentation of glucose under pantothenate deficiency and the reason for the shift to erythritol, acetate, and glycerol fermentation.

Acetates↗
PubMed2002

Electrically enhanced ethanol fermentation by Clostridium thermocellum and Saccharomyces cerevisiae.

Ethanol production by Clostridium thermocellum ATCC 35609 and Saccharomyces cerevisiae ATCC 26603 was improved in an electrochemical bioreactor system. It was increased by 61% with Cl. thermocellum and 12% with S. cerevisiae in the presence of -1.5 V of electric potential. These increases were attributed to high production rates due to regeneration and availability of increased reduced equivalents in the presence of electric potential. The electric current caused considerable shift in the metabolite concentrations on a molar basis in Cl. thermocellum fermentation but less in S. cerevisiae fermentation. Increasing electric potential in Cl. thermocellum fermentation resulted in less acetate and more lactate production. Acetate production was also reduced with increased electric potential in S. cerevisiae fermentation. The high electric potential of -5 V adversely affected the Cl. thermocellum fermentation, but not the S. cerevisiae fermentation even at a high electric potential of -10 V.

Bioreactors↗
PubMed2004

Improvement of fermentative hydrogen production: various approaches.

Fermentation of biomass or carbohydrate-based substrates presents a promising route of biological hydrogen production compared with photosynthetic or chemical routes. Pure substrates, including glucose, starch and cellulose, as well as different organic waste materials can be used for hydrogen fermentation. Among a large number of microbial species, strict anaerobes and facultative anaerobic chemoheterotrophs, such as clostridia and enteric bacteria, are efficient producers of hydrogen. Despite having a higher evolution rate of hydrogen, the yield of hydrogen [mol H2 (mol substrate(-1))] from fermentative processes is lower than that achieved using other methods; thus, the process is not economically viable in its present form. The pathways and experimental evidence cited in the literature reveal that a maximum of four mol of hydrogen can be obtained from substrates such as glucose. Modifications of the fermentation process, by redirection of metabolic pathways, gas sparging and maintaining a low partial pressure of hydrogen to make the reaction thermodynamically favorable, efficient product removal, optimum bioreactor design and integrating fermentative process with that of photosynthesis, are some of the ways that have been attempted to improve hydrogen productivity. This review briefly describes recent advances in these approaches towards improvement of hydrogen yield by fermentation.

Bacteria↗
PubMed2004

Growth rates of Dekkera/Brettanomyces yeasts hinder their ability to compete with Saccharomyces cerevisiae in batch corn mash fermentations.

Growth rates determined by linear regression analysis revealed that Saccharomyces cerevisiae consistently grew more rapidly than Brettanomyces yeasts under a wide array of batch fermentative conditions, including acetic acid stress, in normal gravity (ca. 20 degrees Plato) mashes made from ground corn. Brettanomyces yeasts only grew more rapidly than S. cerevisiae when acetic acid concentrations were elevated to industrially irrelevant levels (>0.45%, w/v). Furthermore, the three Brettanomyces isolates used in this study failed to produce significant quantities of acetic acid under pure culture fermentative conditions. In fact, the small amounts of acetic acid which accumulated in pure culture fermentations of whole corn mash were below the concentration required to inhibit the growth and metabolism of S. cerevisiae. Acetic acid concentrations in pure culture Brettanomyces fermentations exceeded 0.05% (w/v) only in media containing low levels of glucose (<4%, w/v) or when aeration rates were elevated to at least 0.03 vol. air vol.-1 mash min-1. Consequently, it was concluded that Brettanomyces yeasts would not be capable of competing with S. cerevisiae in industrial batch fermentations of whole corn mash based solely on growth rates, nor would they be capable of producing inhibitory concentrations of acetic acid in such fermentations.

Acetic Acid↗
PubMed2005

Extracellular production of a glycolipid biosurfactant, mannosylerythritol lipid, by Candida sp. SY16 using fed-batch fermentation.

Candida sp. strain SY16 produces a glycolipid-type biosurfactant, mannosylerythritol lipid (MEL-SY16), which can reduce the surface tension of a culture broth from 72 to 30 dyne cm(-1) and highly emulsify hydrocarbons when cultured in soybean-oil-containing media. As such, laboratory-scale fermentation for MEL-SY16 production was performed using optimized conditions. In batch fermentation, MEL-SY16 was mainly produced during the stationary phase of growth, and the concentration of MEL-SY16 reached 37 g l(-1) after 200 h. The effect of pH control on the production of MEL-SY16 was also examined in batch fermentation. The highest production yield of MEL-SY16 was when the pH was controlled at 4.0, and the production was significantly improved compared to batch fermentation without pH control. In fed-batch fermentation, glucose and soybean oil (1:1, w/w) were used in combination as the initial carbon sources for cell growth, and soybean oil was used as the feeding carbon source during the MEL production phase. The feeding of soybean oil resulted in the disappearance of any foam and a sharp increase in the MEL production until 200 h, at which point the concentration of MEL-SY16 was 95 g l(-1). Among the investigated culture systems, the highest MEL-SY16 production and volumetric production rate were achieved with fed-batch fermentation.

Candida↗
PubMed2007

Fermentative production of lactic acid from biomass: an overview on process developments and future perspectives.

The concept of utilizing excess biomass or wastes from agricultural and agro-industrial residues to produce energy, feeds or foods, and other useful products is not necessarily new. Recently, fermentation of biomass has gained considerable attention due to the forthcoming scarcity of fossil fuels and also due to the necessity of increasing world food and feed supplies. A cost-effective viable process for lactic acid production has to be developed for which several attempts have been initiated. Fermentation techniques result in the production of either D: (-) or L: (+) lactic acid, or a racemic mixture of both, depending on the type of organism used. The interest in the fermentative production of lactic acid has increased due to the prospects of environmental friendliness and of using renewable resources instead of petrochemicals. Amylolytic bacteria Lactobacillus amylovorus ATCC 33622 is reported to have the efficiency of full conversion of liquefied cornstarch to lactic acid with a productivity of 20 g l(-1) h(-1). A maximum of 35 g l(-1) h(-1) was reported using a high cell density of L. helveticus (27 g l(-1)) with a complete conversion of 55- to 60-g l(-1) lactose present in whey. Simultaneous saccharification and fermentation is proved to be best in the sense of high substrate concentration in lower reactor volume and low fermentation cost. In this review, a survey has been made to see how effectively the fermentation technology explored and exploited the cheaply available source materials for value addition with special emphasis on lactic acid production.

Biomass↗
PubMed2000

Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation.

1,3-Propanediol inhibition during glycerol fermentation to 1,3-propanediol by Clostridium butyricum CNCM 1211 has been studied. The initial concentration of the 1,3-propanediol affected the growth of the bacterium more than the glycerol fermentation. mu(max) was inversely proportional to the initial concentration of 1,3-propanediol (0-65 g l(-1)). For glycerol at 20 g l(-1), the growth and fermentation were completely stopped at an initial 1,3-propanediol concentration of 65 g l(-1). However, for an initial 1,3-propanediol concentration of 50 g l(-1) and glycerol at 70 g l(-1), the final concentration (initial and produced) of 1,3-propanediol reached 83.7 g l(-1)(1.1 M), with complete consumption of the glycerol. Therefore, during the fermentation, the strain tolerated a 1,3-propanediol concentration higher than the initial inhibitory concentration (65 g l(-1)). The addition of 1,2-propanediol or 2,3-butanediol (50 g l(-1)) in the presence of glycerol (50-100 g l(-1)), showed that 2-diols reduced the mu(max) in a similar way to 1,3-propanediol. The measurement of the osmotic pressure of glycerol solutions, diols and diol/glycerol mixtures did not indicate any differences between these compounds. The hypothesis of diol inhibition was discussed. Taking into account the strain tolerance of highly concentrated 1,3-propanediol during fermentation, the fermentation processes for optimising production were considered.

Butylene Glycols↗
PubMed1999

Oxygen starvation induces cell death in Candida shehatae fermentations of D-xylose, but not D-glucose.

Candida shehatae cells, cultivated on D-glucose and D-xylose, were subjected to a shift from fully aerobic to anaerobic fermentative conditions. After anaerobic conditions were imposed, growth was limited to approximately one doubling or less as C. shehatae rapidly entered a stationary phase of growth. Following the shift to anoxia, cell viability rapidly declined and the total cell volume declined in the D-xylose fermentations. Moreover, the cell volume distribution shifted to smaller volumes. Cell viability, measured by plate counts, declined nine times faster for D-xylose fermentations than for D-glucose fermentations. Anaerobic growth did not occur on either D-glucose or D-xylose. Selected vitamins and amino acids did not stimulate anaerobic growth in C. shehatae, but did enhance anaerobic growth on D-glucose in S. cerevisiae. The decline in cell viability and lack of anaerobic growth by C. shehatae were attributed to oxygen deficiency and not to ethanol inhibition. The results shed light on why C. shehatae anaerobic fermentations are not currently practical and suggest that research directed towards a biochemical understanding of why C. shehatae can not grow anaerobically will yield significant improvements in ethanol fermentations from D-xylose.

Aerobiosis↗
PubMed2001

Use of catabolite repression mutants for fermentation of sugar mixtures to ethanol.

Use of agricultural biomass, other than corn-starch, to produce fuel ethanol requires a microorganism that can ferment the mixture of sugars derived from hemicellulose. Escherichia coli metabolizes a wide range of substrates and has been engineered to produce ethanol in high yield from sugar mixtures. E. coli metabolizes glucose in preference to other sugars and, as a result, utilization of the pentoses in hemicellulose-derived sugar mixtures is delayed and may be incomplete. Residual sugar lowers the ethanol yield and is problematic for downstream processing of fermentation products. Therefore, a catabolite repression mutant that simultaneously utilizes glucose and pentoses would be useful for fermentation of complex substrate mixtures. We constructed ethanologenic E. coli strains with a glucose phosphotransferase (ptsG) mutation and used the mutants to ferment glucose, arabinose, and xylose, singly and in mixtures, to ethanol. Yields were 87-94% of theoretical for both the wild type and mutants, but the mutants had an altered pattern of mixed sugar utilization. Phosphotransferase mutants metabolized the pentoses simultaneously with glucose, rather than sequentially. Based upon fermentations of sugar mixtures, a catabolite-repression mutant of ethanologenic E. coli is expected to provide more efficient fermentation of hemicellulose hydrolysates by allowing direct utilization of pentoses.

Biomass↗
PubMed2005

Suitability of a batch in vitro fermentation model using human faecal microbiota for prediction of conversion of flaxseed lignans to enterolactone with reference to an in vivo rat model.

BACKGROUND: In vitro fermentation models have been used widely for studies of shortchain fatty acid (SCFA) formation from carbohydrates, whereas the suitability of these methods for enterolactone (ENL) formation has received less attention. AIM: The aim was to study the suitability of an in vitro fermentation model for prediction of bioconversion of lignans to ENL, to compare the approach with that of an in vivo rat model and to study the SCFA formation in both models. METHODS: Predigested samples of rye bran (R), flaxseed meal (F) alone, or in combination with rye bran (R&F) and a faecal control were incubated in an in vitro fermentation model using human faecal microbiota. In the in vivo experiment rats consumed a non-fibre control diet (C) or diets supplemented either with rye bran (R), flaxseed meal (F) alone, or with their combination (R&F) for four weeks. Enterodiol (END), ENL and SCFA concentrations were measured from in vitro faecal fermentation samples and from the intestinal contents of rats. Plasma ENL concentrations from rats were also measured. RESULTS: The highest ENL production was found in vitro with the F supplement (areas under curve: 740 +/- 4, 7,500 +/- 400, 2,600 +/- 500 and 1,520 +/- 70 nmol x h for the R, F, R&F supplements and faecal control, respectively). In vivo, the concentration of ENL in caecal digesta from flaxseed meal was significantly (P < 0.05) enhanced by the presence of rye bran (medians 261, 407 and 24 nmol/g in the F, R&F and C groups, respectively). No correlation was found between the models regarding ENL production, possibly due to different responses to the presence of rye bran matrix, differences in microbiota or application of a batch in the in vitro fermentation model. Rye bran supplementation enhanced butyrate production both in vitro and in vivo. CONCLUSION: In vitro fermentation and the in vivo rat models responded differently to the presence of rye bran and no correlation with regard to the ENL formation from flaxseed lignans was observed.

4-Butyrolactone↗
PubMed2006

Effects of methylmalonyl-CoA mutase gene knockouts on erythromycin production in carbohydrate-based and oil-based fermentations of Saccharopolyspora erythraea.

In carbohydrate-based fermentations of Saccharopolyspora erythraea, a polar knockout of the methylmalonyl-CoA mutase (MCM) gene, mutB, improved erythromycin production an average of 126% (within the range of 102-153% for a 0.95 confidence interval). In oil-based fermentations, where erythromycin production by the wild-type strain averages 184% higher (141-236%, 0.95 CI) than in carbohydrate-based fermentations, the same polar knockout in mutB surprisingly reduced erythromycin production by 66% (53-76%, 0.95 CI). A metabolic model is proposed where in carbohydrate-based fermentations MCM acts as a drain on the methylmalonyl-CoA metabolite pool, and in oil-based fermentations, MCM acts in the reverse direction to fill the methylmalonyl-CoA pool. Therefore, the model explains, in part, how the well-known oil-based process improvement for erythromycin production operates at the biochemical level; furthermore, it illustrates how the mutB erythromycin strain improvement mutation operates at the genetic level in carbohydrate-based fermentations.

Bacterial Proteins↗
PubMed2006

Improvement in fermentation characteristics of degermed ground corn by lipid supplementation.

With rapid growth of fuel ethanol industry, and concomitant increase in distillers dried grains with solubles (DDGS), new corn fractionation technologies that reduce DDGS volume and produce higher value coproducts in dry grind ethanol process have been developed. One of the technologies, a dry degerm, defiber (3D) process (similar to conventional corn dry milling) was used to separate germ and pericarp fiber prior to the endosperm fraction fermentation. Recovery of germ and pericarp fiber in the 3D process results in removal of lipids from the fermentation medium. Biosynthesis of lipids, which is important for cell growth and viability, cannot proceed in strictly anaerobic fermentations. The effects of ten different lipid supplements on improving fermentation rates and ethanol yields were studied and compared to the conventional dry grind process. Endosperm fraction (from the 3D process) was mixed with water and liquefied by enzymatic hydrolysis and was fermented using simultaneous saccharification and fermentation. The highest ethanol concentration (13.7% v/v) was achieved with conventional dry grind process. Control treatment (endosperm fraction from 3D process without lipid supplementation) produced the lowest ethanol concentration (11.2% v/v). Three lipid treatments (fatty acid ester, alkylphenol, and ethoxylated sorbitan ester 1836) were most effective in improving final ethanol concentrations. Fatty acid ester treatment produced the highest final ethanol concentration (12.3% v/v) among all lipid supplementation treatments. Mean final ethanol concentrations of alkylphenol and ethoxylated sorbitan ester 1836 supplemented samples were 12.3 and 12.0% v/v, respectively.

Culture Media↗