Effect of dissolved O concentration on the Escherichia coli in a cell-recycle bioreactor

In the fermentation of Escherichia coli, a ceramic membrane filter was used in conjunction with a fermenter for cell-recycle operation. The metabolic behaviour, especially the acetic acid production and the specific growth rate, under different concentrations of dissolved O was investigated. An unstructured model was constructed, and it was shown that the observed lower cell density under low dissolved O concentrations was accompanied by large acetic aicd production. However, the concentration of acetic acid was not high enough to cause the observed growth inhibition, and inhibition by other metabolites under low O environment is suspected.     

High-rate continuous production of lactic acid by Lactobacillus rhamnosus in a two-stage membrane cell-recycle bioreactor

It is important to produce L(+)-lactic acid at the lowest cost possible for lactic acid to become a candidate monomer material for promising biodegradable polylactic acid. In an effort to develop a high-rate bioreactor that provides high productivity along with a high concentration of lactic acid, the performance of membrane cell-recycle bioreactor (MCRB) was investigated via experimental studies and simulation optimization. Due to greatly increased cell density, high lactic acid productivity, 21.6 g L(-1) h(-1), was obtained in the reactor. The lactic acid concentration, however, could not be increased higher than 83 g/L. When an additional continuous stirred tank reactor (CSTR) was attached next to the MCRB a higher lactic acid concentration of 87 g/L was produced at significant productivity expense. When the two MCRBs were connected in series, 92 g/L lactic acid could be produced with a productivity of 57 g L(-1) h(-1), the highest productivity among the reports of L(+)-lactic acid that obtained lactic acid concentration higher than 85 g/L using glucose substrate. Additionally, the investigation of lactic acid fermentation kinetics resulted in a successful model that represents the characteristics of lactic acid fermentation by Lactobacillus rhamnosus. The model was found to be applicable to most of the existing data with MCRBs and was in good agreement with Levenspiel's product-inhibition model, and the Luedeking-Piret equation for product-formation kinetics appeared to be effective in representing the fermentation kinetics. There was a distinctive difference in the production potential of cells (cell-density-related parameter in Luedeking-Piret equation) as lactic acid concentration increases over 55 g/L, and this finding led to a more precise estimation of bioreactor performance.     

High-concentration cultivation of Lactococcus cremoris in a cell-recycle reactor

High-cell concentration cultivation of Lactococcus cremoris, a homofermentative lactic acid producer, in a cell-recycle fermentor is described. Cross-flow filtration allowing continuous removal of the inhibitory metabollte, the influence of dilution rate on growth was investigated in total or partial cell-recycle cultures. The dependence of growth characteristics on operating conditions was identified and quantified using lactose as the carbon source. Growth kinetics could be described by both lactate removal efficiency and nutrient availability. Based on physiological observations, biomass and lactic acid productivities were predicted in partial cell-recycle cultures.     

Cultivation of Aspergillus niger in a pilot plant external-loop air-lift bioreactor

Abstract: Changes of the main hydrodynamic and oxygen transfer parameters during Aspergillus niger cultivation in an external-loop air-lift bioreactor of 200 dm³ operating capacity were investigated. The final average concentrations of biomass and citric acid obtained in batch fermentations were about 17 g 1^-1 and 90 g 1^-1, respectively. Significant influence of the increasing biomass concentration on the rheological properties of the broth and operating parameters was found. Volumetric oxygen transfer coefficient. k ^L a , was found to be dependent on the apparent viscosity of the broth with an exponent of -0.984.     

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     

Decolourisation of a pigment plant effluent by Pycnoporus cinnabarinus in a packed-bed bioreactor

Summary The decolourisation of wastewater from a pigment plant by the white-rot fungus Pycnoporus cinnabarinus was studied in a packed-bed bioreactor. Decolourisation was first observed 48 to 72 h after inoculation and was followed using UV/VIS spectrophotometry. An assessment of the inhibitory properties of the effluent on the growth of Pycnoporus cinnabarinus showed that this fungus can tolerate high levels of potentially toxic waste.     

Improvement of a fixed bed bioreactor for plant cell culture

A bioreactor used for cultivation of microbes entrapped in beads was utilized for batch culture of tobacco cells. Tobacco cells were tightly fixed on the cell-attachment net and growth rates of the cells were similar in both the bioreactor and flasks. Furthermore, there was no significant difference in the intracellular biosynthesis of phenylpropanoids between the bioreactor and flask cultures.     

Manufacturing of fermented goat milk with a mixed starter culture of Bifidobacterium animalis and Lactobacillus acidophilus in a controlled bioreactor

AIMS: This work was undertaken to study the feasibility and the characteristics of a fermented product made of goat milk, using a mixed starter culture of Bifidobacterium animalis and Lactobacillus acidophilus under controlled conditions, and to determine their survival in the fermented milk during refrigerated storage. METHODS AND RESULTS: Goat milk was inoculated with Lact. acidophilus and Bif. animalis mixed starter, fermented in a glass bioreactor with controlled temperature (37 degrees C) and anaerobiosis, and monitored for growth and acidification. The fermented milk was then stored for 10 days under refrigeration, and monitored daily for starter microflora survival and pH changes. Lact. acidophilus viable counts reached a maximum of 7.1 x 10(8) colony-forming units (CFU) ml(-1), and Bif. animalis a maximum of 6.3 x 10(7) CFU ml(-1) by 20 h of fermentation. During refrigerated storage, both strains exhibited a good survival, with viable numbers remaining essentially constant throughout the experiment, whereas the pH of the fermented milk dropped slightly. CONCLUSIONS: Mixed cultures of Bif. animalis and Lact. acidophilus may be used to produce fermented goat milk with high counts of both probiotic strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Goat milk fermented with Bif. animalis and Lact. acidophilus can be manufactured as an alternative probiotic dairy product.     

植物组织培养生物反应器技术研究进展

从植物大规模组织培养的特点、反应器类型和反应器中微环境等方面介绍了生物反应器技术在药用植物微繁殖和天然产物细胞生产中的研究进展。     

Flow regimes in a two phase reversed flow jet loop bioreactor

Reversed flow jet loop bioreactors (RFJLB) have been used extensively for 2 or 3 phase biochemical reactions. From visual observations and gas holdup data, 3 distinct flow regimes are identified in RFJLB, namely: (1) Bubble free regime (BFR), where bubbles are observed in the draft tube only; (2) Transition regime (TR), where bubbles are observed in both the draft tube and the annulus, but without circulation; and (3) Complete bubble circulation regime (CBCR), where bubbles circulate in both the draft tube and annulus. CBCR is the most desirable regime, since the reactor operation in this regime gives a higher gas holdup and mass transfer rate than in the other two regimes. In the present study, the hydrodynamic behavior of RFJLB was investigated under various operational and geometrical conditions, such as gas and liquid velocity and nozzle configuration. Factors affecting the critical liquid circulation velocity (CLCV) above which the CBCR is established were identified and evaluated quantitatively.     

Mixing intensity studies in a pilot plant stirred bioreactor with an electromagnetic drive

The design and methodology of a stirring intensity measuring device, SIMD-f3, are described. A low noise action electromagnetic drive is developed and applied. Measurements in water demonstrate the fundamental validity of the device. Measurements in air–water and different solutions of carboxymethyl cellulose (CMC) do not contradict the physical interpretation. Potential applications could embrace optimization of mixers design and mixing regimes, control of technological processes, scale-up and scale-down. The low noise action electromagnetic drive provides a possibility of carring out correct mixing measurements and elimination of contamination when cultivating microorganisms.     

Concentration multiplicity in a draft tube fluidized-bed bioreactor involving two limiting substrates

Concentration multiplicity in a two-phase or three-phase draft tube fluidized-bed bioreactor containing biofloc particles is studied. The kinetics of biological reactions considered involve two limiting substrates. The necessary and sufficient conditions for concentration multiplicity in both the biofilm and bioreactor are examined in terms of effectiveness factor, inlet and bulk concentration of substrates, and liquid flow rate. Hysteresis behavior in both the biofilm and bioreactor and multiplicity of concentration profiles in the biofilm are also discussed.     

Degradation of oxadiazon in a bioreactor integrated in the water closed circuit of a plant nursery

Hardy ornamental nursery stock (HONS) use fertigation as a rational supply of nutrients all along the growth cycle of plants. Nevertheless, that frequency of irrigation increases the risks of nutrient and herbicide leaching and subsequent contamination of the waste water. Therefore, systems of water treatment are required in plant nurseries. Pseudomonas fluorescens strain CG5 cells were immobilized on a ceramic support (sepiolite) contained in a 150 l-bioreactor for the biodegradation of the herbicide oxadiazon in the re-circulated leachates. Percolation and inundation operating processes were assayed in the bioreactor. The levels of oxadiazon in water samples were determined by solid phase extraction on C18 columns and gas chromatography with electron capture detection system. Fifty eight percolation cycles resulted in a significant reduction of oxadiazon up to just 5 microg l(-1) at the outlet. Similar herbicide elimination was achieved after two consecutive 68-h inundation periods. In addition, it was found that the nutrient content in the waste water at the bioreactor outlet was sufficient to support an adequate plant growth.     

Development of a helical-ribbon impeller bioreactor for high-density plant cell suspension culture

A double helical-ribbon impeller (HRI) bioreactor with a 11-L working volume was developed to grow high-density Catharanthus roseus cell suspensions. The rheological behavior of this suspension was found to be shear-thinning for concentrations higher than 12 to 15 g DW . L(-1). A granulated agar suspension of similar rheological properties was used as a model fluid for these suspensions. Mixing studies revealed that surface baffling and bottom profiling of the bioreactor and impeller speeds of 60 to 150 rpm ensured uniform mixing of suspensions. The HRI power requirement was found to increase singnificantly for agar suspensions higher than 13 g DW . L(-1), in conjunction with the effective viscosity increase. Oxygen transfer studies showed high apparent surface oxygen transfer coefficients (k(L)a approximately 4 to 45 h(-1)) from agar suspensions of 30 g DW . L(-1) to water and for mixing speeds ranging from 120 to 150 rpm. These high surface k(I)a values were ascribed to the flow pattern of this bioreactor configuration combined with surface bubble generation and entrainment in the liquid phase caused by the presence of the surface baffles. High-density C. roseus cell suspension cultures were successfully grown in this bioreactor without gas sparging. Up to 70% oxygen enrichment of the head space was required to ensure sufficient oxygen supply to the cultures so that dissolved oxygen concentration would remain above the critical level (>/=10% air saturation). The best mixing speed was 120 rpm. These cultures grew at the same rate ( approximately 0.4 d(-1)) and attained the same high biomass concentrations ( approximately 25 to 27 g DW . L(-1), 450 to 500 g filtered wet biomass . L(-1), and 92% to 100% settled wet biomass volume) as shake flask cultures. The scale-up potential of this bioreactor configuration is discussed.     

Impact of two starter cultures on proteolysis in Kashkaval cheese

Summary Kashkaval cheese is produced with a traditional yogurt starter culture S. thermophilus 13a + Lb. delbrueckii ssp. bulgaricus 2–11. The present paper has investigated the contribution of a selected starter culture (Lactococcus lactis ssp. lactis C11 + Streptococcus thermophilus P23 + Lactobacillus casei ssp. casei RP5) for proteolysis of Kashkaval (A) in comparison with a traditional yogurt culture (B) and soluble nitrogen (at pH 4.6 and in 12% TCA) and free amino acids as indicators of Kashkaval ripeness. After the microflora was isolated and differentiated, the largest count of mesophilic cocci (69%) and lower counts of thermophilic cocci (19.8%) and mesophilic lactobacilli (11.2%) were found in cheddared curd A, whereas in cheddared curd B thermophilic cocci (69%) prevailed over thermophilic lactobacilli (30%). Hot-brining of curd at 72 °C for 2 min destroyed 91 and 84.5%, respectively, of the starter microflora A and B and two batches of Kashkaval started ripening with 3.9 × 10⁸ c.f.u. g⁻¹ and 3.4 × 10⁸ c.f.u. g⁻¹. The ripening of Kashkaval cheese occurred mainly under the influence of the starter microflora. Ripening of Kashkaval A occurred with dominating presence of Lactobacillus casei ssp. casei RP5 from 64% at day 30 to 95.2% at day 90. In Kashkaval B the participation of Lactobacillus delbrueckii ssp. bulgaricus 2–11 increased from 36.3 to 39.9%, however it always remained relatively smaller (1.5–2.3-fold) than that of thermophilic cocci. Great activity of transformation of pH 4.6-soluble nitrogen into TCA-soluble nitrogen in Kashkaval A was registered. The high proteolytic activity of starter culture A shortened the ripening process by 30 days (30-day-old Kashkaval A had 17.3% level of proteolysis, 29.9% depth of proteolysis). Kashkaval B reached satisfactory ripeness properties when it was 60 days old (20.2% level of proteolysis, 24.9% depth of proteolysis). The high activity of amino acid release mainly by Lactobacillus casei ssp. casei RP5 and to a lesser extent by the cocci caused accumulation of a considerable amount of free amino acids in ripe Kashkaval A (421.9 mg (100 g)⁻¹ for 30-day-old Kashkaval). In ripe 30-day-old Kashkaval A the concentration of free amino acids was three times higher than in Kashkaval B, with domination of lysine, leucine, phenylalanine, valine and threonine.     

Shear stress effects on plant cell suspension cultures in a rotating wall vessel bioreactor

A rotating wall vessel, designed for growth of mammalian cells under microgravity, was used to study shear effects on Taxus cuspidata plant suspension cell cultures. Shear stress, as quantified by defined shear fields of Couette viscometers, improved specific cell growth rates and was detrimental to volumetric product formation rates. Received 5 January 1998/ Accepted in revised form 8 December 1998     

Contained and high-level production of recombinant protein in plant chloroplasts using a temporary immersion bioreactor

Chloroplast transformation is a promising approach for the commercial production of recombinant proteins in plants. However, gene containment still remains an issue for the large-scale cultivation of transplastomic plants in the field. Here, we have evaluated the potential of using tobacco transplastomic cell suspensions for the fully contained production of a modified form of the green fluorescent protein (GFP+) and, a vaccine antigen, fragment C of tetanus toxin (TetC). Expression of these proteins in cell suspension cultures (and calli) was much less than in leaves, reaching 0.5%-1.5% of total soluble protein (TSP), but still produced 2.4-7.2 mg/L of liquid culture. Much better expression levels were achieved with a novel protein production platform in which transgenic cell suspension cultures were placed in a temporary immersion bioreactor in the presence of Thidiazuron to initiate shoot formation. GFP+ yield reached 660 mg/L of bioreactor (33% TSP), and TetC accumulated to about 95 mg/L (8% TSP). This new production platform, combining the rapid generation of transplastomic cell suspension cultures and the use of temporary immersion bioreactors, is a promising route for the fully contained low-cost production of recombinant proteins in chloroplasts.     

Biomass axial distribution in airlift bioreactor with yeast and plant cells

This study was aimed at determining the degree of biomass homogeneity in the various parts of an internal loop airlift bioreactor, thus verifying the assumption, often made in bioreactor studies, of a well-mixed liquid-biomass system. Following characterization of the hydrodynamics of the vessel with water, the axial biomass distribution in the riser and downcomer was determined for plant and yeast cell suspensions of 5.8, 8.5, and 12.5 g DW/L Phaseolus vulgaris and of 30 and 46 g DW/L Saccharomyces cerevisiae. The airlift bioreactor with a surface ratio A(D)/A(D) of 1.04 and aspect ratio of 4.95 was investigated under various aeration rates. The yeast cells were found to be distributed practically uniformly throughout the vessel at the aeration rates of 0.1-1.45 vvm. However, in the case of the denser and cluster-forming plant cells, a clear trend of a gradual bio-mass accumulation in the downcomer, a slightly lower but uniform biomass loading in the riser, and a slightly higher biomass concentration in the gas-liquid separator was observed at the lower aeration rates of 0.1-0.61 vvm. In the case of powderized calcium carbonate (55g/L) often used in fermentations of organic acids, a slight trend of a gradual accumulation of solids towards the bottom parts in both the downcomer and riser was observed. A better representative sampling location, in terms of solids and biomass loading, seems to be in the middle part of the vessel. It is suggested that airlift bioreactors with higher aspect ratios (>5) may be prone to a more significant inhomogeneity of solids (biomass and particles).