Alcoholic fermentation by Zymomonas mobilis: Effect of initial substrate on physiological parameters

Summary The influence of initial substrate concentration on fermentation kinetics of Zymomonas mobilis on glucose has been studied in batch cultures over the range 50–190 gl^-1 glucose. With increasing glucose, parameters relative to growth ( and R_GX) are more rapidly and more noticeably affected than those connected with ethanol production (p and R_GP). The water content of the cells is also affected.     

Spore production ofPenicillium roqueforti by simulated solid state fermentation

Summary A culture technique, based on the growth of a microorganism on inert porous particles (e. g. pozzolano) impregnated and continuously fed with substrate is applied to the growth and spore production ofPenicillium roqueforti. The composition and the feed rate of the medium can be controlled, and the biomass is directly estimated.P. roqueforti exhibits a diauxic growth on the medium containing sucrose and malt extract used, and 1.5 10⁹ spores/g pozzolano may be obtained.     

Bioconversion of gitoxigenin by immobilized plant cells in a column bioreactor

Summary Daucus carota cells immobilized in a Ca-alginate performed the bioconversion of gitoxigenin to 5-hydroxygitoxigenin in a column bioreactor. The smooth spherical shape of the alginate beads was preserved for more than three weeks. The bioreactor was functional for more than thirty days as detected by the bioconversion activity. The rate of bioconversion was influenced by means of aeration.Issued as National Research Council of Canada Publication Number 19556     

Ethanol production with Saccharomyces cerevisiae at potassium-limited aerobic growth conditions

Summary The specific ethanol productivity withSaccharomyces cerevisiae grown aerobically in a chemostat at a growth rate of 0.17 hr^–1 was found to increase from zero to 13 mmol/g cell dry matter·h when the potassium content in the substrate used was decreased to 0.05 mol/kg glucose. 78% of the glucose metabolized were converted to ethanol under these aerobic growth conditions.     

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.     

Linear growth in microbial cultures limited by accumulated substrate

Summary The linear growth phase in cultures limited by intracellular (conservative) substrate is represented by a flat exponential curve. Within the range of experimental errors, the presented model fits well the data from both batch and continuous cultures ofEscherichia coli, whose growth is limited in that way.List of symbols D dilution rate, h^–1 - K_S saturation constant, g.L^–1 - S concentration of the limiting substrate, g.L^–1 - S_i concentration of the limiting substrate accumulated in the cells, g.g^–1 - S_o initial concentration of the limiting substrate, g.L^–1 - t time of cultivation, h - t₁ time of exhaustion of the limiting substrate from medium, h - t_o beginning of exponential phase, h - X biomass concentration, g.L^–1 - X₁ biomass concentration at the time of exhaustion of the limiting substrate from the medium, g.L^–1 - X_o biomass concn. at the beginning of exponential phase, g.L^–1 - biomass concn. at steady-state, g.L^–1 - Y growth yield coefficient (biomass/substrate) - specific growth rate, h^–1 - _m maximum specific growth rate, h^–1     

Utilization of palm kernel cake for production of β-mannanase by Aspergillus niger FTCC 5003 in solid substrate fermentation using an aerated column bioreactor

The production of β-mannanase from palm kernel cake (PKC) as a substrate in solid substrate fermentation (SSF) was studied using a laboratory column bioreactor. The simultaneous effects of three independent variables, namely incubation temperature, initial moisture content of substrate and airflow rate, on β-mannanase production were evaluated by response surface methodology (RSM) on the basis of a central composite face-centered (CCF) design. Eighteen trials were conducted in which Aspergillus niger FTCC 5003 was cultivated on PKC in an aerated column bioreactor for seven days under SSF process. The highest level of β-mannanase (2117.89 U/g) was obtained when SSF process was performed at incubation temperature, initial moisture level and aeration rate of 32.5°C, 60% and 0.5 l/min, respectively. Statistical analysis revealed that the quadratic terms of incubation temperature and initial moisture content had significant effects on the production of β-mannanase (P < 0.01). A similar analysis also demonstrated that the linear effect of initial moisture level and an interaction effect between the initial moisture content and aeration rate significantly influenced the production of β-mannanase (P < 0.01). The statistical model suggested that the optimal conditions for attaining the highest level of β-mannanase were incubation temperature of 32°C, initial moisture level of 59% and aeration rate of 0.5 l/min. A β-mannanase yield of 2231.26 U/g was obtained when SSF process was carried out under the optimal conditions described above.     

Solid substrate fermentation for cellulase production using palm kernel cake as a renewable lignocellulosic source in packed-bed bioreactor

Palm kernel cake (PKC), is an agro-industrial residue created in the palm oil industry, and large quantities of PKC are produced in Malaysia. Sustainable development of the palm oil industry in Malaysia demands an economical technology for the environmentally friendly utilization of PKC in industrial utility systems. This research was carried out to evaluate the use of PKC in the production of cellulase by the cultivation of Aspergillus niger FTCC 5003 in a laboratory packed-bed bioreactor for seven days. A central composite design was used to perform eighteen trials of solid substrate fermentation under selected conditions of incubation temperature, initial moisture content of substrate, and airflow rate. Experimental results showed that a cellulase yield of 244.53 U/g of dry PKC was obtained when 100 g of PKC was hydrolyzed at an incubation temperature of 32.5°C, an initial moisture level of 60%, and an aeration rate of 1.5 L/min/g PKC. An empirical second-order polynomial model was adjusted to the experimental data to evaluate the effects of the studied operating variables on cellulase production. The statistical model revealed that the quadratic term for initial moisture content had a significant effect on the production of cellulase (P < 0.01). The regression model also indicated that the quadratic terms for incubation temperature and interaction effects between initial moisture content and aeration rate significantly influenced cellulase production (P < 0.05). The empirical model determined that the optimum conditions for cellulase production were an incubation temperature of 31.0°C, an initial moisture content of 59.0% and an airflow rate of 1.55 L/min/g PKC.     

Solid state fermentation of dried citrus peel byAspergillus niger

Summary Solid state fermentation of dried citrus peel was studied in a packed bed reactor withAspergillus niger QH-2. When no nitrogen source was added the growth was limited. When urea and/or ammonium sulphate were added in the proportion of 0.63 g N/100 g solid dry substrate a diauxie was observed and the final content of crude protein was higher than 10%. The results of a factorial design show that ammonium sulphate has a significant effect on the specific growth rate.     

Evaporative temperature and moisture control in solid substrate fermentation

Summary An integrated computerized control system, consisting of temperature and moisture sensors, a variable relative humidity air stream and water sprayers was used to control temperature and moisture in the solid substrate fermentation of extruded corn withRhizopus oligosporus in a 15 l rotary drum fermenter. Dry air was blown through the substrate to force evaporative cooling, balanced by spraying of cold water to maintain constant moisture.     

A two stage continuous process for the production of thermogelable curdlan-type exopolysaccharide

Summary A laboratory-scale, two-stage continuous process for the production of curdlan-type exopolysaccharide has been operated in steady-state for 500hr. Two continuous flow, constant volume fermenters are connected in series. A stable, curdlan-producing strain of Alcaligenes faecalis var myxogenes ATCC 31749 is grown aerobically in a nitrogen-limited chemostat operating near D_max at 0.24 hr^–1. The effluent is introduced directly into a second larger constant volume fermenter which is being simultaneously fed a glucose solution at a fixed rate. Under sub-optimal conditions associated with curdlan production, the observed Qp was 0.05 g curdlan/g cell/hr. At a biomass level of 4 g/L in the second stage, curdlan was present at 10 g DW/L and the volumetric productivity was 0.2 g/g cell/hr. The substrate (glucose) conversion efficiency was 42%. The process is described in patents applied for on behalf of George Weston Ltd. (Toronto, Canada).     

Spectrophotometric titrations of ferricytochrome C with ferrohexacyanide in the pH range 5 to 7

Spectrophotometric titrations were conducted on the system horse heart ferricytochromec plus ferrohexacyanide in the pH range 5 to 7 and at temperatures 8, 18, 22 and 28°C. A difference extinction coefficient for reducedvs. oxidized cytochromec at 550 nm of 21 mmol^–1cm^–1 was used in part of the evaluations. On the assumption that only one electron-transferlinked proton dissociation is effective for both ferro- and ferricytochromec in this pH range, various possible models are developed with only three conforming with the experimental pH dependence of the spectrophotometric equilibrium constant. The data conform best to a model with protonic dissociation constants between pH 5 and 7 such that the reduced cytochromec species is at least a factor of 3 more acidic than the one for oxidized cytochromec (with pK_H 6). This interpretation holds least for the data at 22°C, which points to a structural rearrangement at about this temperature (Czerlinski and Bracokova, 1973; Zabinski and Czerlinski, 1974; Zabinski, et al., 1974). While the extinction coefficient of ferrocytochromec shows no significant change with pH and temperature, the one for ferricytochromec does: it is about 5% larger at pH 5 than at pH 7 (550 nm). Graphs for the absorption change of ferricytochromec (pH 7 as reference) document the details over the wavelength range 500 to 750 nm.     

Growth of the yeast Hansenula anomala with nitrate as sole source of nitrogen under aerobic and anaerobic conditions

Summary The oxygen requirement ofHansenula anomala growing in batch culture on nitrate as sole source of nitrogen was examined. An aeration rate of 0.03 vvm or a constant oxygen partial pressure of 0.01 bar is sufficient for optimal growth.     

Microbial production of citric acid in fixed-bed column bioreactors

Summary Aspergillus niger NRRL 567 was cultured on the solid substrate, fruit pomace, in fixed-bed column bioreactors to produce citric acid. The rates of substrate consumption and citric acid production were strongly influenced by (1) the rate of aeration, (2) the fermentation temperature, (3) the initial moisture content of the substrate, and (4) the size of the inoculum. This culture method yielded approximately 130 g of citric acid per kg of apple pomace fermented under optimum conditions.     

Effect of aeration on large-scale cultures of plant cells

Summary The large scale culture of plant cells in bioreactors presents problems of a different nature to those seen with micro-organisms. One particular problem is concerned with the mode of culture aeration and the effects of aeration on cell growth. Data is presented which illustrates this problem through the effects of varying rates of aeration on both the initial growth rate and maximum growth rate of cells of Catharanthus roseus.     

Photosynthetic ability in dark-grown Reboulia hemisphaerica and Barbula unguiculata cells in suspension culture

Suspension cultured cells of the liverwort, Reboulia hemisphaerica and of the moss, Barbula unguiculata were independently subcultured in the medium containing 2% glucose in the dark or in the light for more than one year, and the photosynthetic activities of the final cultures were determined. Throughout the culture period light-grown cells of both species contained high amount of chlorophyll (4 to 34 g mg^–1 dry weight) and showed a high photosynthetic activity (10 to 84 mol O₂ mg^–1 chlorophyll h^–1). Dark-grown cells of R. hemisphaerica showed the same level of chlorophyll content and photosynthetic O₂ evolving activity as light-grown cells. Although chlorophyll content in dark-grown B. unguiculata cells was ten-fold lower than that in light-grown cells, the photosynthetic activity of these dark-grown cells was higher than that of light-grown cells based on chlorophyll content.     

Continuous culture of a recombinantEscherichia coli and plasmid maintenance for tryptophan production

Summary Production of tryptophan by a temperature sensitive recombinant microorganism (Escherichia coli W3110 trpLDtrpR ^ts tna ^– (pCRT185)) was investigated. In a single-stage continous culture, at an elevated temperature, 42°C (derepressed condition), tryptophan concentration increased in an early phase of the fermentation, and then gradually decreased with time. The reduction in the production rate was mostly due to the segregation of the plasmid and subsequent increase of plasmid-free cells. However, the plasmid could be maintained stable at 37°C, with repressed condition oftrp-operon, over 200 generations. A two-stage continuous culture system, i.e. cell growth was maintained in the first stage at 37°C and gene expression was induced in the second stage at 42°C, was therefore tested to improve the performance of the fermentation system. Operation of the two-stage system showed that the plasmid stability was significantly improved, and the specific rate of tryptophan production was maintained almost constant for more than 500 hours in the second stage.     

Production of pullulan by a fed-batch fermentation

Summary In pullulan production from sucrose byAureobasidium pullulans, a sugar concentration higher than 5% (w/v) inhibited cell growth and the production of exopolysaccharide. By a fed-batch fermentation, the inhibitory effects of the high sugar concentration were overcome and 58.0 g/1 of exopolysaccharide were obtained from 10% sucrose.Abbreviations m, n relationship parameters for the growth and non-growth associated product formation - X, Xmax biomass and maximum biomass concentration (g cell/1) - P product concentration (g exopolysaccharide/1) - specific growth rate of cell (hr^–1)     

Effect of irrigation from a point source (trickling) on oxygen flux and on root extension in the soil

A two-dimensional trickle-irrigated soil model was examined in order to determine its aeration regime. Oxygen diffusion rate (O.D.R.) was used as an index of the soil aeration regime, and its influence on the development of root systems was determined. Volumetric soil air content was calculated from soil water tension data, using a retention curve.The root system was markedly concentrated at the periphery of the trickle-irrigated soil volume, while in the center there were few roots. An exponential correlation was found between root distribution and O.D.R., in which 20×10^–8g O₂×cm^–2×min^–1 was the critical value for root growth. There was a linear correlation between O.D.R. and volumetric air content which was affected by diffusion distance.     

Refining and unifying the upper limits of the least limiting water range using soil and plant properties

The least limiting water range (LLWR) was introduced as an integrated soil water content indicator, measuring the impact of mechanical impedance, oxygen and water availability on water uptake and crop growth. However, a rigorous definition of the upper limit of the LLWR using plant physiological and soil physical concepts was not given. We introduce in this study an upper limit of the LLWR, based on soil physical and plant physiological properties. We further evaluate the sensitivity of this boundary to different soil and crop variables, and compare the sensitivity of the upper limit of the LLWR to previous definitions of soil water content at field capacity. The current study confirms that the upper limit of the LLWR can be predicted from knowledge of the soil moisture characteristic curve, plant root depth and oxygen consumption rate. The sensitivity analysis shows further that the upper limit of the LLWR approaches the volumetric soil water content at saturation when the oxygen consumption rate by plants becomes less than 2 µmol m^?3 s^?1. When plants are susceptible to aeration (e.g. potato and avocado), there is a big difference between the upper limit of the LLWR and the soil water content at field capacity, in particular for sandy soils. Results also show that the soil water content at aeration porosity corresponding to 10% cannot be considered as an appropriate upper limit of LLWR because it does not appropriately reflect the crop water requirements. Similar poor results are obtained when considering the soil water content at matric potential ?0.033 MPa or when defining the soil water content at field capacity based on drainage flux rate. It is observed that the upper limit of the LLWR is higher than either soil water content at ?0.033 MPa matric potential or soil water content at field capacity as based on drainage flux rate, especially in sandy soils.