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At least 109 records · Page 6Linked to original sources

PubMed2001

Kojic acid production in an airlift bioreactor using partially hydrolyzed raw corn starch.

In a culture of Aspergillus oryzae MK-107-39 in a 3-l airlift bioreactor, kojic acid was not produced when glucose/wheat germ medium (GM1) was used. However, when a jar fermentor was used, the kojic acid yield was high. A suitable medium for culture in an airlift bioreactor consisting of partially hydrolyzed corn starch and a small amount of corn steep liquor (CSL) (SM1) was selected. In the cultivation in the airlift bioreactor using SM1, nearly 40 g/l of kojic acid was produced, which was the same as the amount produced in the jar fermentor containing GM1. The optimum aeration rate for the airlift bioreactor was 2.0 vvm (0.66 cm/s of superficial linear velocity (Vs)). The cost of SM1 using the airlift bioreactor was reduced to 40% that of GM1 using the jar fermentor. Furthermore, the energy cost of kojic acid production using SM1 in the airlift bioreactor was less than one-fourth of that for the jar fermentor using GM1.

Journal Article↗

PubMed2001

Performance of a partially packed charcoal pellet bioreactor for acetic acid fermentation.

The performance of a partially packed charcoal pellet bioreactor was compared to that of a fully packed bioreactor for aerobic acetic acid production. In the fully packed charcoal pellet bioreactor, it was considered that the shortening of an actual retention time of the culture broth limited the bioreactor performance under high dilution rate and high aeration conditions. By reducing the filling ratio of charcoal pellets to 44%, which increased the actual retention time of the culture broth, the maximum productivity increased from 3.9 g/l/h in the fully packed bed bioreactor to 5.7 g/l/h in the partially packed bioreactor without affecting the operational stability.

Journal Article↗

PubMed2002

Enhanced anthocyanin production from grape callus in an air-lift type bioreactor using a viscous additive-supplemented medium.

An N-medium containing carboxymethyl cellulose (CMC) was applied to an air-lift type bioreactor culture of grape (Vitis vinifera cv. Bailey alicant A.) callus, and anthocyanin production was investigated. Grape callus grew well at an air flow rate of 80 ml/min and anthocyanin production was significantly increased in the N-medium, reaching 17 mg/l after 7 d of culture. The anthocyanin content of the N-medium was about two times higher than that of the conventional medium without CMC. The effect of air flow rate was also investigated within the range from 40 to 160 ml/min. A twofold increase in anthocyanin content was obtained at all the air flow rates tested in the N-medium. The distribution of grape callus size obtained after 7 d of the bioreactor culture was investigated. The average callus size was 490 mum which was 1.6 times larger than that obtained in the conventional medium. It was found that large calli with a relatively high anthocyanin pigment content were formed in the bioreactor culture using the N-medium. The fluid dynamics in the bioreactor was also investigated at three points (top, middle and bottom) in the bioreactor by laser doppler velocimetry. The average axial velocity of the circulated medium was 0.4 times lower than that of the conventional medium while their average radial velocities were almost the same (zero). The standard deviation of radial velocity fluctuation in the N-medium was also 0.4 times less than that in the conventional medium. These results suggest that turbulent flow occurred in the bioreactor culture using the conventional medium and the degree of turbulent flow decreased significantly when 0.8% CMC was added to the medium to prepare the N-medium. A change of the flow pattern is considered to be the cause of the decrease in hydrodynamic stress, resulting in enhanced pigment production due to the enlargement of the callus.

Journal Article↗

PubMed2000

Mathematical modeling as a tool to investigate the design and operation of the zymotis packed-bed bioreactor for solid-state fermentation.

Zymotis bioreactors for solid-state fermentation (SSF) are packed-bed bioreactors with internal cooling plates. This design has potential to overcome the problem of heat removal, which is one of the main challenges in SSF. In ordinary packed-bed bioreactors, which lack internal plates, large axial temperature gradients arise, leading to poor microbial growth in the end of the bed near the air outlet. The Zymotis design is suitable for SSF processes in which the substrate bed must be maintained static, but little is known about how to design and operate Zymotis bioreactors. We use a two-dimensional heat transfer model, describing the growth of Aspergillus niger on a starchy substrate, to provide guidelines for the optimum design and operation of Zymotis bioreactors. As for ordinary packed-beds, the superficial velocity of the process air is a key variable. However, the Zymotis design introduces other important variables, namely, the spacing between the internal cooling plates and the temperature of the cooling water. High productivities can be achieved at large scale, but only if small spacings between the cooling plates are used, and if the cooling water temperature is varied during the fermentation in response to bed temperatures.

Aspergillus niger↗

PubMed2003

Development of foamed emulsion bioreactor for air pollution control.

A new type of bioreactor for air pollution control has been developed. The new process relies on an organic-phase emulsion and actively growing pollutant-degrading microorganisms, made into a foam with the air being treated. This new reactor is referred to as a foamed emulsion bioreactor (FEBR). As there is no packing in the reactor, the FEBR is not subject to clogging. Mathematical modeling of the process and proof of concept using a laboratory prototype revealed that the foamed emulsion bioreactor greatly surpasses the performance of existing gas-phase bioreactors. Experimental results showed a toluene elimination capacity as high as 285 g(toluene) m(-3) (reactor) h(-1) with a removal efficiency of 95% at a gas residence time of 15 s and a toluene inlet concentration of 1-1.3 g x m(-3). Oxygen limited the reactor performance at toluene concentration above about 0.7-1.0 g x m(-3); consequently, performance was significantly improved when pure oxygen was added to the contaminated air. The elimination capacity increased from 204 to 408 g x m(-3) h(-1) with >77% toluene removal at toluene inlet concentrations of 2-2.2 g x m(-3). Overall, the results show that the performance of the FEBR far exceeds that of currently used bioreactors for air pollution control.

Air Pollutants↗

PubMed2005

Development, parallelization, and automation of a gas-inducing milliliter-scale bioreactor for high-throughput bioprocess design (HTBD).

A novel milliliter-scale bioreactor equipped with a gas-inducing impeller was developed with oxygen transfer coefficients as high as in laboratory and industrial stirred-tank bioreactors. The bioreactor reaches oxygen transfer coefficients of >0.4 s(-1). Oxygen transfer coefficients of >0.2 s(-1) can be maintained over a range of 8- to 12-mL reaction volume. A reaction block with integrated heat exchangers was developed for 48-mL-scale bioreactors. The block can be closed with a single gas cover spreading sterile process gas from a central inlet into the headspace of all bioreactors. The gas cover simultaneously acts as a sterile barrier, making the reaction block a stand-alone device that represents an alternative to 48 parallel-operated shake flasks on a much smaller footprint. Process control software was developed to control a liquid-handling system for automated sampling, titration of pH, substrate feeding, and a microtiter plate reader for automated atline pH and atline optical density analytics. The liquid-handling parameters for titration agent, feeding solution, and cell samples were optimized to increase data quality. A simple proportional pH-control algorithm and intermittent titration of pH enabled Escherichia coli growth to a dry cell weight of 20.5 g L(-1) in fed-batch cultivation with air aeration. Growth of E. coli at the milliliter scale (10 mL) was shown to be equivalent to laboratory scale (3 L) with regard to growth rate, mu, and biomass yield, Y(XS).

Aerobiosis↗

PubMed2005

Tissue engineering of human cartilage in bioreactors using single and composite cell-seeded scaffolds.

Chondrocytes isolated from human fetal epiphyseal cartilage were seeded under mixed conditions into 15-mm-diameter polyglycolic acid (PGA) scaffolds and cultured in recirculation column bioreactors to generate cartilage constructs. After seeding, the cell distributions in thick (4.75 mm) and thin (2.15 mm) PGA disks were nonuniform, with higher cell densities accumulating near the top surfaces. Composite scaffolds were developed by suturing together two thin PGA disks after seeding to manipulate the initial cell distribution before bioreactor culture. The effect of medium flow direction in the bioreactors, including periodic reversal of medium flow, was also investigated. The quality of the tissue-engineered cartilage was assessed after 5 weeks of culture in terms of the tissue wet weight, glycosaminoglycan (GAG), total collagen and collagen type II contents, histological analysis of cell, GAG and collagen distributions, and immunohistochemical analysis of collagen types I and II. Significant enhancement in construct quality was achieved using composite scaffolds compared with single PGA disks. Operation of the bioreactors with periodic medium flow reversal instead of unidirectional flow yielded further improvements in tissue weight and GAG and collagen contents with the composite scaffolds. At harvest, the constructs contained GAG concentrations similar to those measured in ex vivo human adult articular cartilage; however, total collagen and collagen type II levels were substantially lower than those in adult tissue. This study demonstrates that the location of regions of high cell density in the scaffold coupled with application of dynamic bioreactor operating conditions has a significant influence on the quality of tissue-engineered cartilage.

Bioreactors↗

PubMed2005

Continuous plug-flow bioreactor: experimental testing with Pseudomonas putida culture grown on benzoate.

The goals of this work were to test the feasibility of a continuous plug-flow (PF) bioreactor and to compare the growth in the PF bioreactor to that in a batch bioreactor. A culture of Pseudomonas putida was pumped through a tube made of Teflon with varying residence times. The culture was aerated by pumping of air simultaneously with liquid medium to provide air bubbles along the tubular culture. When the residence time in the PF bioreactor was greater than the time needed to reach the stationary phase in batch mode, the maximum biomass density reached in PF mode was the same as the maximum density reached in the batch bioreactor, and benzoate (the only carbon and energy source) was completely consumed. The drawbacks for practical application of PF were found to be fluctuations of cell concentration in the outflow cultural liquid due to cell aggregation, significant cell adhesion to the inner wall of Teflon tubing, and inadequate aeration.

Benzoates↗

PubMed2005

Perfusion bioreactor system for human mesenchymal stem cell tissue engineering: dynamic cell seeding and construct development.

Human mesenchymal stem cells (hMSCs) have great potential for therapeutic applications. A bioreactor system that supports long-term hMSCs growth and three-dimensional (3-D) tissue formation is an important technology for hMSC tissue engineering. A 3-D perfusion bioreactor system was designed using non-woven poly (ethylene terepthalate) (PET) fibrous matrices as scaffolds. The main features of the perfusion bioreactor system are its modular design and integrated seeding operation. Modular design of the bioreactor system allows the growth of multiple engineered tissue constructs and provides flexibility in harvesting the constructs at different time points. In this study, four chambers with three matrices in each were utilized for hMSC construct development. The dynamic depth filtration seeding operation is incorporated in the system by perfusing cell suspensions perpendicularly through the PET matrices, achieving a maximum seeding efficiency of 68%, and the operation effectively reduced the complexity of operation and the risk of contamination. Statistical analyses suggest that the cells are uniformly distributed in the matrices. After seeding, long-term construct cultivation was conducted by perfusing the media around the constructs from both sides of the matrices. Compared to the static cultures, a significantly higher cell density of 4.22 x 10(7) cell/mL was reached over a 40-day culture period. Cellular constructs at different positions in the flow chamber have statistically identical cell densities over the culture period. After expansion, the cells in the construct maintained the potential to differentiate into osteoblastic and adipogenic lineages at high cell density. The perfusion bioreactor system is amenable to multiple tissue engineered construct production, uniform tissue development, and yet is simple to operate and can be scaled up for potential clinical use. The results also demonstrate that the multi-lineage differentiation potential of hMSCs are preserved even after extensive expansion, thus indicating the potential of hMSCs for functional tissue construct development. The system has important applications in stem cell tissue engineering.

Adipocytes↗

PubMed2006

Flow characterization of a wavy-walled bioreactor for cartilage tissue engineering.

Cartilage tissue engineering requires the use of bioreactors in order to enhance nutrient transport and to provide sufficient mechanical stimuli to promote extracellular matrix (ECM) synthesis by chondrocytes. The amount and quality of ECM components is a large determinant of the biochemical and mechanical properties of engineered cartilage constructs. Mechanical forces created by the hydrodynamic environment within the bioreactors are known to influence ECM synthesis. The present study characterizes the hydrodynamic environment within a novel wavy-walled bioreactor (WWB) used for the development of tissue-engineered cartilage. The geometry of this bioreactor provides a unique hydrodynamic environment for mammalian cell and tissue culture, and investigation of hydrodynamic effects on tissue growth and function. The flow field within the WWB was characterized using two-dimensional particle-image velocimetry (PIV). The flow in the WWB differed significantly from that in the traditional spinner flask both qualitatively and quantitatively, and was influenced by the positioning of constructs within the bioreactor. Measurements of velocity fields were used to estimate the mean-shear stress, Reynolds stress, and turbulent kinetic energy components in the vicinity of the constructs within the WWB. The mean-shear stress experienced by the tissue-engineered constructs in the WWB calculated using PIV measurements was in the range of 0-0.6 dynes/cm2. Quantification of the shear stress experienced by cartilage constructs, in this case through PIV, is essential for the development of tissue-growth models relating hydrodynamic parameters to tissue properties.

Animals↗

PubMed2006

Model of the mass transport to the surface of animal cells cultured in a rotating bioreactor operated in micro gravity.

A mathematical model is used to investigate the transport of dissolved oxygen from the bulk fluid to the surface of aggregates of animal cells cultured in a rotating bioreactor. These aggregates move through different regions of the bioreactor with a local flow field and concentration distribution that vary with time. The time variation of the Sherwood number and the surface concentration for a range of parameters typical of a cell science experiment executed in the Rotating Wall Perfused Vessel (RWPV) bioreactor in space are investigated. The Reynolds numbers experienced by the aggregate are generally low (Re < 1) and the Peclet numbers range from O(1) to O(100). Comparison of the results from the numerical solution of the mathematical model with those from a quasi-steady model, using a steady-state correlation for mass transport on a sphere, indicate that the quasi-steady assumption is not a good model to compute the instantaneous Sherwood number. This indicates a significant history effect in the Sherwood number response to the variations of acceleration of the aggregates in the bioreactor. A high resistance to the mass transport from the bulk fluid to the surface of the aggregate exists for the bioreactor operated in micro gravity. The difference between the surface concentration and the free stream concentration was as high as 30% for aggregates larger than 3 mm. Diffusion reduces the variations of the free stream concentration resulting in a nearly constant value for the concentration at the surface of the aggregates.

Animals↗

PubMed2007

Flow modeling in a novel non-perfusion conical bioreactor.

We have developed a bioreactor vessel design which has the advantages of simplicity and ease of assembly and disassembly, and with the appropriately determined flow rate, even allows for a scaffold to be suspended freely regardless of its weight. This article reports our experimental and numerical investigations to evaluate the performance of a newly developed non-perfusion conical bioreactor by visualizing the flow through scaffolds with 45 degrees and 90 degrees fiber lay down patterns. The experiments were conducted at the Reynolds numbers (Re) 121, 170, and 218 based on the local velocity and width of scaffolds. The flow fields were captured using short-time exposures of 60 microm particles suspended in the bioreactor and illuminated using a thin laser sheet. The effects of scaffold fiber lay down pattern and Reynolds number were obtained and correspondingly compared to results obtained from a computational fluid dynamics (CFD) software package. The objectives of this article are twofold: to investigate the hypothesis that there may be an insufficient exchange of medium within the interior of the scaffold when using our non-perfusion bioreactor, and second, to compare the flows within and around scaffolds of 45 degrees and 90 degrees fiber lay down patterns. Scaffold porosity was also found to influence flow patterns. It was therefore shown that fluidic transport could be achieved within scaffolds with our bioreactor design, being a non-perfusion vessel. Fluid velocities were generally same of the same or one order lower in magnitude as compared to the inlet flow velocity. Additionally, the 90 degrees fiber lay down pattern scaffold was found to allow for slightly higher fluid velocities within, as compared to the 45 degrees fiber lay down pattern scaffold. This was due to the architecture and pore arrangement of the 90 degrees fiber lay down pattern scaffold, which allows for fluid to flow directly through (channel-like flow).

Bioreactors↗

PubMed2001

New pulsatile bioreactor for fabrication of tissue-engineered patches.

To date, one approach to tissue engineering has been to develop in vitro conditions to ultimately fabricate functional cardiovascular structures prior to final implantation. In our current experiment, we developed a new pulsatile flow system that provides biochemical and biomechanical signals to regulate autologous patch-tissue development in vitro. The newly developed patch bioreactor is made of Plexiglas and is completely transparent (Mediport Kardiotechnik, Berlin). The bioreactor is connected to an air-driven respirator pump, and the cell culture medium continuously circulates through a closed-loop system. We thus developed a closed-loop, perfused bioreactor for long-term patch-tissue conditioning, which combines continuous, pulsatile perfusion and mechanical stimulation by periodically stretching the tissue-engineered patch constructs. By adjusting the stroke volume, the stroke rate, and the inspiration/expiration time of the ventilator, it allows various pulsatile flows and different levels of pressure. The whole system is a highly isolated cell culture setting, which provides a high level of sterility, gas supply, and fits into a standard humidified incubator. The bioreactor can be sterilized by ethylene oxide and assembled with a standard screwdriver. Our newly developed bioreactor provides optimal biomechanical and biodynamical stimuli for controlled tissue development and in vitro conditioning of an autologous tissue-engineered patch.

Biocompatible Materials↗

PubMed2004

Quantitative analysis of three-dimensional fluid flow in rotating bioreactors for tissue engineering.

Tissue engineering has emerged as a viable alternative to the problem of organ and tissue shortage. Our laboratory has developed matrices for bone tissue engineering based on sintered spherical particles and, using bioreactor technology, has demonstrated the ability to produce highly mineralized matrices in vitro. In this study, porous microcapsule scaffolds were developed for bone tissue engineering in the high aspect ratio vessel rotating bioreactor. The motion of individual microcapsules as well as scaffolds in the bioreactor were studied by numerical simulation and in situ imaging analysis. Results show that spherical microcapsules with density less than the surrounding fluid exhibited two motions: (1) a periodic circular orbit with tangential speed equal to the free fall speed of the particle, and (2) an inward radial migration of the circular orbit toward the center of the bioreactor vessel. Lighter-than-water scaffolds were fabricated by sintering poly(lactic-co-glycolic acid) hollow microcarriers with diameter from 500 to 860 microm into a fixed three-dimensional geometry with approximately 30% pore volume and 180 to 190 microm median pore size. Scaffolds were fabricated with aggregate densities ranging from 0.65 g/mL and 0.99 g/mL by appropriate combinations of hollow and solid microcarriers within the scaffold. Scaffold velocity in the bioreactor for the above range of densities was accurately predicted by numerical simulation and ranged from 100 mm/s to 3 mm/s. Maximum shear stress estimation due to media flow over the exterior of the scaffold ranged from 0.3 N/m(2) to 0.006 N/m(2). Internal perfusion velocity through scaffolds also was calculated and ranged from 13 mm/s to 0.2 mm/s. Estimates of maximum interior shear stress ranged from 0.03 to 0.0007 N/m(2). These analytical methods provide an excellent vehicle for the study of bone tissue synthesis in three-dimensional culture with fluid flow.

Bioreactors↗

PubMed2005

A GPIIb/IIIa bioreactor for specific treatment of immune thrombocytopenic purpura, an autoimmune disease. Preparation, in vitro characterization, and preliminary proof-of-concept animal studies.

Immune thrombocytopenic purpura (ITP) is an autoimmune disease that affects thousands of Americans each year. The resulting thrombocytopenia, which develops from destruction of platelets (PLT) by anti-PLT autoantibodies (APAb), is often associated with hemorrhagic complications. Existing therapies are not effective and are associated with significant morbidity. Recently, a new treatment modality using plasmapheresis with a Protein-A column has shown some clinical promise. Yet, although this method would remove the pathogenic APAb, it would also deplete protective antibodies, thereby weakening the body's self-defense system. Because about 80% of patients with ITP develop APAb against the GPIIb/IIIa antigens on PLT, a novel approach of attaching a GPIIb/IIIa-linked bioreactor with an extracorporeal circuit is suggested herein to achieve highly effective/specific APAb removal and overcome shortcomings of plasmapheresis in treating ITP. A hollow fiber-based bioreactor device was fabricated, and GPIIb/IIIa antigens were immobilized onto the inner lumens of the hollow fibers by using the epichlorohydrin activation method. An optimized bioreactor containing a loading of 1.63 mg GPIIb/IIIa/g fibers and adsorption capacity of 1.9 mg 7E3/g fibers was developed. Preliminary proof-of-concept investigation using a 7E3-induced thrombocytopenic rat model (which mimicked clinical ITP) was carried out. A complete (100%) return of PLT counts to their initial levels was observed in rats within 6 h after the GPIIb/IIIa bioreactor treatment. In addition, a rapid restoration of WBC counts in the treated rats was also found. These preliminary findings shed light of promise of using the GPIIb/IIIa bioreactor approach in achieving highly improved ITP therapy.

Animals↗

PubMed2004

Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes.

GOALS, SCOPE AND BACKGROUND: From 2005, deposition of organic waste will be banned in Sweden. Likewise, in Germany and Austria, similar bans are being planned, and further countries will probably follow. Thus, there is a need to develop new methods and to refine established techniques for sludge management in the whole of the European Union. For this end, there is also an urgent need for appropriate ecotoxicological approaches to elucidate and assess the hazard potential of sewage sludge. Therefore, the present study was designed to assess the capacity of various established sludge treatment methods using different oxygen regimes to degrade recalcitrant nitro-substituted organic compounds and reduce their toxicity. Sewage sludge samples from a wastewater treatment plant in Sweden (Cambrex Karlskoga AB, industrial area Björkborn) receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives were processed with different sludge treatment methods. Among other treatment methods, bioreactors (for anaerobic and aerobic sludge treatment) were used. In the present investigation, a battery of in vitro bioassays was employed to compare the cytotoxic and genotoxic potentials of different fractions of sludge samples in order to elucidate whether the treatments were suitable to reduce the toxicity of the sludge. METHODS: In order to investigate the cytotoxicity of the extracts of treated and untreated sludge samples, the acute cytotoxicity test with the permanent cell line RTL-W1 was used. Genotoxicity was tested by means of the comet assay (single cell gel electrophoresis) with RTL-W1 cells, and mutagenicity was assessed with the Ames test using the Salmonella typhimurium strains TA98, TA98NR and TA100. Sludge toxicity was tested in different fractions of organic extracts produced by acetone and hexane extractions. The subsequent clean-up procedure (silica gel chromatography and elution with hexane and dichloromethane) resulted in two fractions, a lipophilic hexane-fraction and a semi-lipophilic dichloromethane-fraction. For the genotoxicity and mutagenicity tests, these fractions were reunited at equal ratios. RESULTS AND DISCUSSION: The acute cytotoxicity test with RTL-W1 cells revealed a high cytotoxic potential for the semi-lipophilic DM-fractions of all sludge samples with NR50 values (= effective concentration for 50% cell death in the neutral red test) from 8.9 up to 20 mg sludge d.w./ml medium. A low cytotoxic potential for the hexane fractions of the untreated sludge samples (NR50 400 to > 400 mg sludge d.w./ml medium) was observed, whereas the hexane fractions of the treated sludge samples showed elevated cytotoxicity increasing further with treatment in the bioreactors. The comet assay indicated that three out of eight of the reunited fractions had a significant genotoxic potential. Whereas the genotoxic potential of one sample treated anaerobically was very high with an induction factor of 11.6, a similar sample (taken from the same anaerobic reactor four months later) and one untreated sample showed lower potentials. The samples treated in another anaerobic bioreactor as well as the samples treated aerobically showed no genotoxic potential. Results indicate that aerobic treatment was basically adequate for reducing the genotoxicity of the sludge, whereas anaerobic treatment was only partly useful for reduction of genotoxicity. The Ames test revealed a very high mutagenic potential for the reunited fractions of the untreated sludge samples with strain TA98 (maximum induction factors (IFmax) up to 45) and a relatively high potential for one of the samples treated aerobically (S2, IFmax = 18 (TA98, S9-)), thus documenting the suitability of both anaerobic and aerobic treatments to reduce the mutagenicity of the samples, however, with the aerobic treatment being less effective. CONCLUSIONS: Overall, none of the microbiological treatments for wastewater sludge in bioreactors was found to be ideal for general toxicity reduction of the sludge samples. Whereas cytotoxicity of the sludge increased or levelled off in most cases following either treatment, genotoxicity both increased or decreased after anaerobic treatment, depending on the specific sample. However, mutagenicity could generally be reduced by anaerobic treatment and, to a lesser degree, by aerobic treatment. RECOMMENDATIONS AND PERSPECTIVES: The complex modification of the diverse damage potentials of sludge sample extracts by use of an in vitro biotest battery following treatment for toxicity reduction in bioreactors showed that considerations of different toxicological endpoints is essential for an adequate hazard assessment. Whereas in the case of cytotoxicity reduction, the reactors proved ineffective, mutagenicity could be reduced significantly at least in some cases in this case study.

Biological Assay↗

PubMed2003

Homogeneous batch cultures of Aspergillus oryzae by elimination of wall growth in the Variomixing bioreactor.

A novel principle for mixing and aeration in stirred bioreactors, named Variomixing, was developed. Four baffles are rotated intermittently at a rotational speed slower or similar to the speed of a centrally placed axial flow impeller. Rotational speeds of the baffles and impeller of 5-10 and 500-600 rpm, respectively, results in the highly turbulent flow regime characteristic of conventional bioreactors with high mixing and mass transfer capacities. Stagnant zones around crevices and crannies in which wall growth may commence are avoided since the baffles are never completely at rest. Increasing the rotational speed of the baffles (5 s every 5 min), so that it follows the speed of the impeller (500-600 rpm), cancels the effect of the baffles and a deep vortex and high peripheral liquid flow rates at the reactor wall develop. The vortex ensures that also the head-space of the reactor wall is flushed and any deposits removed. The filamentous fungus Aspergillus oryzae has been grown in batch cultures in the Variomixing bioreactor. Compared to conventional laboratory-scale bioreactors, in which more than 30% of all biomass was found attached to walls, less than 2% of the total A. oryzae biomass was found on the walls in the Variomixing bioreactor.

Aerobiosis↗

PubMed2001

Shear stress enhances microcin B17 production in a rotating wall bioreactor, but ethanol stress does not.

Stress, including that caused by ethanol, has been shown to induce or promote secondary metabolism in a number of microbial systems. Rotating-wall bioreactors provide a low stress and simulated microgravity environment which, however, supports only poor production of microcin B17 by Escherichia coli ZK650, as compared to production in agitated flasks. We wondered whether the poor production is due to the low level of stress and whether increasing stress in the bioreactors would raise the amount of microcin B17 formed. We found that applying shear stress by addition of a single Teflon bead to a rotating wall bioreactor improved microcin B17 production. By contrast, addition of various concentrations of ethanol to such bioreactors (or to shaken flasks) failed to increase microcin B17 production. Ethanol stress merely decreased production and, at higher concentrations, inhibited growth. Interestingly, cells growing in the bioreactor were much more resistant to the growth-inhibitory and production-inhibitory effects of ethanol than cells growing in shaken flasks.

Bacteriocins↗