The effect of CO2 ventilation on kinetics and yields of cell-mass and ethanol in batch cultures ofZymomonas mobilis

Summary The effect of CO₂ removal by continuous sparging of N₂ in batch cultures ofZymomonas mobilis (ATCC10988) was examined. N₂ sparging considerably reduces lag times in batch cultures, possibly because of continuous removal of CO₂ from the culture media. Ventilation of CO₂ from culture media results in an increase of about 15% in the average specific growth rate and about 12% in the cell-mass yield with no noticeable trend in the average specific glucose uptake and ethanol production rates. The overall ethanol yield on glucose, however, decreases slightly by 5%. Analysis of ventilated experiments show that the CO₂ production is directly coupled with the ethanol formation but not necessarily with the cell-mass production, indicating a decoupling of growth from ethanol production. Further, comparison of ventilated and non-ventilated experiments rules out the possibility of CO₂ accumulation in the culture media as a factor responsible for increasing growth inhibition and decoupling of growth from ethanol fermentation at increasing initial glucose concentrations in batch cultures.     

The effect of various atmospheric conditions on the 2,3-butanediol fermentation from glucose byBacillus polymyxa

The examination of the effect of N₂, air and O₂ on the glucose to 2,3-butanediol fermentation byBacillus polymyxa showed that N₂ sparging resulted in best 2,3-butanediol production at low yeast extract concentration (0.5%, w/v) whereas aeration produced best results with high yeast extract levels (1.2%, w/v). However, under all atmospheric conditions, improvements in rates and yields of 2,3-butanediol production and rates of glucose utilization were observed with high yeast extract. Regardless of the yeast extract levels, highest concentrations of ethanol and acetoin were obtained with N₂ sparging and aeration respectively. No acetoin accumulated under anaerobic (N₂) conditions and no ethanol accumulated with aeration. The rate of glucose utilization, in all fermentations, was highest under N₂ and lowest with O₂ sparging. In addition to the biochemical results, morphological observations with O₂, N₂ and air sparging are also reported.NRCC No. 23868     

The production of ethanol by immobilized yeast cells

Saccharomyces cerevisiae cells were immobilized in calcium alginate beads for use in the continuous production of ethanol. Yeasts were grown in medium supplemented with ethanol to selectively screen for a culture which showed the greatest tolerance to ethanol inhibition. Yeast beads were produced from a yeast slurry containing 1.5% alginate (w/v) which was added as drops to 0.05M CaCl₂ solution. To determine their optimum fermentation parameters, ethanol production using glucose as a substrate was monitored in batch systems at varying physiological conditions (temperature, pH, ethanol concentration), cell densities, and gel concentration. The data obtained were compared to optimum free cell ethanol fermentation parameters. The immobilized yeast cells examined in a packed-bed reactor system operated under optimized parameters derived from batch-immobilized yeast cell experiments. Ethanol production rates, as well as residual sugar concentration were monitored at different feedstock flow rates.     

Effect of calcium,manganese and lithium on growth and cardenolide content in cell suspension cultures of Digitalis thapsi L.

Cell suspension cultures of Digitalis thapsi were grown in Murashige and Skoog medium under continuous light. The effects of the absence of CaCl₂, elevation of the MnSO₄ concentration from 0.1 mM to 5 mM or the addition of 100 M LiCl on their growth and digoxin production were investigated. The elimination of calcium reduced growth and viability of cultures but promoted digoxin formation. An increase of the MnSO₄ concentration or the addition of LiCl resulted in higher digoxin content. Under such conditions growth was not affected.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BA N⁶ benzyladenine     

An investigation of ethanol inhibition and other limitations occurring during the fermentation of concentrated whey permeate byKluyveromyces fragilis

Based on the well-known fact thatKluyveromyces fragilis strains show sub-optimal performance when grown in concentrated whey permeate, previously optimized medium was investigated for possible limitations appearing at high concentrations. Shaken flask cultures showed that no additional vitamin or mineral sources were required when the optimized amount of yeast extract was added to the concentrated permeate. Several aspects of the ethanol inhibition of the growth ofK. fragilis NRRL 665 were investigated in continuous culture. The maximum ethanol concentration tolerated by this yeast, i.e. 45 g/l, was much lower than commonly reported for other strains. Ethanol and biomass production were also influenced by the increased ethanol concentration of the medium. At 31 g/l of alcohol product yield was reduced to 0.23 g/g whereas biomass yield was 0.05 g/g. Some evidence suggested that residence time and residual lactose concentration played a significant role in modulating the toxic effect of ethanol.     

Production of fructose syrup by selective removal of glucose from hydrolyzed Jerusalem artichoke juice

Summary The study shows that the yeastSaccharomyces cerevisiae ATCC 36859 can be successfully used for the production of fructose syrup from glucose-fructose mixtures or from Jerusalem artichoke juice by the conversion of glucose to ethanol. During these processes fructose concentration was unchanged.Ethanol yield (Y_P/S), based on glucose consumed in Jerusalem artichoke juice, and ethanol concentration were 0.428 g/g and 1.7% (w/v) respectively. When the juice was supplemented with glucose higher ethanol concentrations were attained but with lower ethanol yields.     

D-Xylose fermentation to ethanol bySchizosaccharomyces pombe cloned with xylose isomerase gene

Summary Schizosaccharomyces pombe cloned with the xylose isomerase gene from E. coli is able to grow on YNB and YMP broths containing xylose as the sole carbon source. This yeast can ferment D-xylose to ethanol directly; however, the ethanol production rate and the yield were dependent on the nitrogen source. With the YMP broth as a nitrogen source, the final ethanol concentration can reach 3.7% (w/v), and the ethanol yield was 80% of the theoretical value based on the amount of xylose that was metabolized. The ethanol production is slow, and the xylitol production is still very active; apparently, the limiting step is the isomerization of xylose to xylulose.     

Ethanol production from Jerusalem artichoke juice using flocculent cells of Kluyveromyces marxianus

Summary Flocculent cells ofKluyveromyces marxianus SM 16-10 were used for batch production of ethanol from the inulin sugars derived from Jerusalem artichoke tubers. Using 20% initial sugar concentration, a maximum ethanol concentration of 92 g/l was achieved in 7 h, when the flocculent cell concentration was 30 g dry wt./l bioreactor volume. The same flocculent cells were used repeatedly for 7 batch runs starting with fresh medium at the beginning of each run. The ethanol yield was found to be almost constant at about 94% of the theoretical for all the 7 batch cycles, while the maximum ethanol production rate increased from 17.21 g ethanol/1/h during the first batch run to 21 g ethanol/1/h during the last batch run.     

The effect of temperature on the kinetics of ethanol production by strains of Zymomonas mobilis

Summary Two strains of Z. mobilis were evaluated for temperature sensitivity between 25°C and 40°C. At higher temperatures the cell viability, biomass yield, ethanol yield and final ethanol concentration decreased, and there was evidence of increased ethanol inhibition. However the kinetic parameters , q_s and q_p were largely unaffected by temperature over this range.     

Ethanol production by zymomonas mobilis: Effect of temperature on cell growth,ethanol production and intracellular ethanol accumulation

Summary The kinetic behaviour of Zymomonas mobilis is studied at temperatures from 27 °C to 34.5 °C. Increases of temperature (above a critical value) have a negative effect on the yield of ethanol, mainly by raising the maintenance coefficient. Cell growth is less inhibited by the ethanol accumulation inside the cell than is the fermentative pathway. The specific rate of ethanol production is depressed when the intracellular ethanol concentration is maximal. An increase of temperature enhances this phenomenon.     

The inhibitory effect of ethanol on ethanol production by Zymomonas mobilis

Summary In an effort to establish the reasons for the limitations in the final ethanol concentration of Zymomonas mobilis fermentation, the effects of CO₂ and ethanol on the fermentation were investigated using continuous and fed-batch cultivation systems. The nucleation and stripping out of CO₂ from the fermenter using diatomaceous earth or nitrogen gas or both exhibited a profound effect on the glucose uptake rate during the early stages of fed-batch fermentation, but did not improve final ethanol yields. The addition of ethanol together with above mentioned experiments confirmed conclusively that ethanol inhibition is responsible for the final ethanol concentration obtainable during Zymomonas mobilis fermentation. The final concentration lies between 90 and 110 gl⁻¹ or approximately 12–15% (v/v) ethanol.     

Conversion of sugar-beet particles to ethanol by the bacteriumZymomonas mobilis in solid-state fermentation

Summary The possibility of usingZymomonas mobilis as the microorganism, in solid-state fermentation of sugar-beet particles was investigated. The major factors affecting the process were investigated and related to ethanol yield and productivity. Ethanol yield of 0.48 g/g sugar, volumetric productivity of 12 g/L h, and final ethanol concentration of 130 g/L show the good performance ofZ.mobilis in a solid-state fermentation.     

The effect of temperature,pH, and initial glucose concentration on the kinetics of ethanol production by Zymomonas mobilis in batch fermentation

Summary Zymomonas mobilis, strain ATCC 10988, was used to evaluate the effects of pH (5.0 to 8.0), temperature (30°C to 40°C), and initial glucose concentration (75 g/l to 150 g/l) on the kinetics of ethanol production from glucose using batch fermentation. Specific ethanol production rate was maximum and nearly constant over a pH range of 6.0 to 7.5. End-of-batch ethanol yield and specific growth rate were insensitive to pH in the range of 5.0 to 7.5. End-of-batch ethanol yield was maximum and nearly constant between 30°C and 37°C but decreased by 24% between 37°C and 40°C. All other kinetic parameters are greatest at 34°C. End-of-batch ethanol yield is maximum at an initial glucose concentration of 100 g/l. Specific growth rate reaches a maximum at 75 g/l, but specific ethanol production rate decreases throughout the range. The optimum initial glucose concentration of 100 g/l gives the highest ethanol yield at a specific ethanol production rate less than 10% below the maximum observed.     

Toxicity analysis of encapsulation solutions and polymers in the cultivation of insect cells

Summary Microencapsulation of insect cells, hosts for baculovirus expression systems, requires that the encapsulation reagents and membrane-forming materials be non-toxic to the cells. Various encapsulation polymers (poly-l-lysine, chitosan and alginate) and solutions (KCl, CaCl₂, CHES and sodium citrate) were tested for their toxicity toSpodoptera frugiperda cells. The effects of varying polymer molecular weight and concentration on cell viability were also investigated.     

Thermophilic methanogenesis from sugar beet pulp by a defined mixed bacterial culture

Summary Thermophilic degradation of sugar beet pulp was studied in batch cultures at 55°C by different associations of bacteria, includingClostridium thermocellum,Methanobacterium sp. andMethanosarcina MP.C. thermocellum produced acetate, succinate, methanol, ethanol, H₂ and CO₂. The coculture ofC. thermocellum andMethanobacterium sp. produced trace amounts of ethanol and succinate; acetate concentration was about three times higher than in theC. thermocellum monoculture. The association of this coculture withMethanosarcina MP produced 5.5 mmol CH₄/g dry weight sugar beet pulp.     

Continuous production of ethanol from a glucose,xylose and arabinose mixture by a flocculent strain ofPichia stipitis

Summary Enhanced rates of continuous ethanol production by a flocculent strain ofPichia stipitis from a sugar mixture (xylose 75%, glucose 20%, arabinose 5%) were attained using a single-stage gas lift tower fermentor. With a substrate feed of 50g/l, the biomass accumulated at a level near 50g/l, showed a maximum and stable ethanol productivity of 10.7 g/l.h, with a substrate conversion of 80%; the ethanol yield reached 0.41g/g. In these operating conditions, similar performances were obtained when D.xylose alone was supplied.     

Production of ethanol and biomass from various carbohydrates byKluyveromyces fragilis

Summary Growth ofKluyveromyces fragilis NRC 2475 and the production of ethanol by the yeast were studied in the media containing one of the following sugars: glucose, lactose, galactose, or a glucose-galactose (50% 50%) mixture as a carbon source.The largest biomass yield and the lowest yield of ethanol were obtained in the medium containing glucose. The medium containing galactose gave the lowest yield of biomass and the largest yield of ethanol. When lactose was used for the growth and production of ethanol the obtained results for both biomass and ethanol were between those obtained with glucose and galactose.The ethanol productivities, expressed in terms of ethanol produced either per unit of cells, or per unit of cells and time, were the highest in the system with galactose and the lowest in that with glucose.     

The effect of aeration on D-xylose fermentation byPachysolen tannophilus,Pichia stipitis,Kluyveromyces marxianus andCandida shehatae

Summary The fermentation of D-xylose byPachysolen tannophilus Y2460,Pichia stipitis Y7124,Kluyveromyces marxianus Y2415 andCandida shehatae Y12878 was investigated in aerobic, anaerobic and microaerophilic batch cultures. The aeration rate greatly influenced the fermentations; growth, rate of ethanol production and oxidation of ethanol are affected. Of the strains tested,Pichia stipitis appears superior; under anaerobic conditions it converts D-xylose (20 g/l) to ethanol with a yield of 0.40 g/l and it exhibits the highest ethanol specific productivity (3.5 g of ethanol per g dry cell per day) under microaerophilic conditions.     

Effect of calcium and sodium salts on ethanol production in high sugar fermentation by free cells ofZymomonas mobilis

Summary Addition of calcium carbonate enhanced ethanol production byZymomonas mobilis ZM4 and a mutant (ZMI₂), especially at higher concentrations (200–400 g/L) of glucose and sucrose, as well as at higher temperature (42°C) by the mutant. Calcium and sodium carbonates neutralized the acid produced in the medium and enhanced the ethanol production. The Na salts were less effective in the parent strain and were not favourable for the mutant. Ca²⁺ ions played a direct role in augmenting ethanol production as evidenced by the effect of calcium chloride at controlled pH (5.5).     

Ethylene and ethane production in response to salinity stress

Abstract Ethylene and ethane production in mung bean hypocotyl sections were evaluated as possible indicators of stress due to contact with four salts that are common in natural sites. Ethylene production decreased with increasing concentrations of applied NaCl and KCl. When CaCl₂ was applied, the ethylene evolution was greater. However, when MgCl₂ was applied, ethylene evolution remained high then decreased and at higher salt concentrations again showed an increase. NaCl (up to 0.1 kmol m^?1) and KCl (up to 0.5 kmol m^?3) caused a concentration-dependent increase in ethane production. The ethane production with CaCl₂ was the lowest among the salts tested and only a minute increase was noticed with the increase of concentration from 0.01 to 1 kmol m^?3. Ethane production showed a distinct maximum at 0.2 kmol m^?3 MgCl₂. The introduction of 0.01 kmol m^?3 CaCl₂, as well as anaerobic conditions obtained by purging vials with N₂, eliminated that high ethane production. Respiratory activity of the mung bean hypocotyl sections in MgCl₂ concentrations from 0 to 0.5 kmol m^?3 was correlated with ethane but not with ethylene production. The ethane/ethylene ratio showed three patterns for the four salts tested.