Investigation of liquid-solid hydrodynamic boundary layers and oxygen requirements in hairy root cultures.

Rates of oxygen uptake, growth and alkaloid production by hairy roots in submerged culture were investigated using a recirculation reactor allowing operation at high liquid velocities for removal of hydrodynamic boundary layers. Measurements were performed at dissolved oxygen tensions of 31-450% air saturation. Critical oxygen concentrations for Atropa belladonna hairy roots were above air saturation, viz. 100-125% air saturation for oxygen uptake and 150% air saturation for growth, demonstrating that these roots cultivated in reactors with air sparging are oxygen-limited. The critical oxygen tension for oxygen uptake by Solanum aviculare hairy roots was 75% air saturation. Both the specific oxygen uptake rate and specific growth rate of A. belladonna hairy roots were dependent on the mass (g dry weight) of roots present; even in the absence of boundary layers, growth did not remain exponential over the entire culture period. Cryo-scanning electron microscopy showed that hairy roots grown submerged in liquid medium were covered with thick layers of hydrated mucilage and root hairs, representing a significant additional barrier to oxygen transfer. Roots protruding out of the liquid medium showed no evidence of mucilage accumulation. The specific oxygen demand of A. belladonna root tips was 3.3-11.5 times higher than for the remainder of the roots, the ratio increasing as the dissolved oxygen tension was reduced. Specific growth rates, biomass yields from sugar, and atropine levels were maximum at around 150% air saturation, but decreased significantly with oxygen concentrations above ca. 200%.     

Evaluation of Spray Cycle Bioreactor Using L-Alanine Degradation by Candida maltosa

The oxygen-supply capability of a spray cycle reactor was evaluated by using it for oxidative degradation of L-alanine. The volumetric oxygen transfer coefficient, k_La, was evaluated as a parameter for the oxygen supply. The liquid circulation rate in the spray cycle reactor was represented in terms of the number of circulations. The k_La increased with the number of circulations, especially by stirring in the reservoir vessel, reaching 272/h at 4.4/min of circulation numbers. This value was 1.4 times higher than that without stirring. The L-alanine degradation rate increased as the cell growth was promoted, and as the circulation numbers increased. Finally, the spray cycle reactor was evaluated by the specific degradation rate. This rate increased in proportion to the k_La, and was 8.8 times higher than that in the jar fermentor, suggesting that the spray cycle reactor is superior for oxygen-demanding fermentation.     

Root hairiness: effect on fluid flow and oxygen transfer in hairy root cultures

The effect of root hairiness on fluid flow and oxygen transfer in hairy root cultures was investigated using wild-type, transgenic and root-hair mutants of Arabidopsis thaliana. The root hair morphologies of the A. thaliana lines were hairless, short hairs, moderately hairy (wild-type) and excessively hairy, and these morphologies were maintained after transformation of seedlings with Agrobacterium rhizogenes. Filtration experiments were used to determine the permeability of packed beds of roots; permeability declined significantly with increasing root hairiness as well as with increasing biomass density. Hairy roots of wild-type A. thaliana grew fastest with a doubling time of 6.9 days, but the hairless roots exhibited the highest specific oxygen uptake rate. In experiments using a gradientless packed bed reactor with medium recirculation, the liquid velocity required to eliminate external mass transfer boundary layer effects increased with increasing root hairiness, reflecting the greater tendency towards liquid stagnation near the surface of roots covered with hairs. External critical oxygen tensions also increased with increasing root hairiness, ranging from 50% air saturation for hairless roots to ca. 150% air saturation for roots with excessive root hairs. These results are consistent with root hairs providing a significant additional resistance to oxygen transfer to the roots, indicating that very hairy roots are more likely than hairless roots to become oxygen-limited in culture. This investigation demonstrates that root hairiness is an important biological parameter affecting the performance of root cultures and suggests that control over root hair formation, either by use of genetically modified plant lines or manipulation of culture conditions, is desirable in large-scale hairy root systems.     

Dual aerobic hollow-fiber bioreactor for cultivation of Streptomyces aureofaciens

Streptomyces aureofaciens (ATCC 12416c) was grown in the interstitial region formed by a parallel arrangement of three hollow silicone tubules contained within a microporous polypropylene hollow fiber. Liquid-soluble nutrients were supplied by diffusion across the polypropylene fiber to the interstitial cell-containing region whereas air or oxygen was provided by diffusion from the silicone tubule lumina to the cell mass. In this bioreactor, S. aureofaciens grew to high cell densities (greater than 10(11) cells/cm(3)) and the culture so-obtained continously synthesized the secondary metabolite tetracycline. The volumetric productivity of tetracycline based on the interstitial volume was 90 mug/ml/h and based on the total reactor volume was 5.5 mug/mL/h. The high surface area-to-volume ratio afforded by the cylindrical configuration together with spatially distinct conduits to continuously transport liquids and gases, each of which may be nutrients or products of biosynthesis, to or from a tissuelike cell mass provides an alternative to the conventional air- or oxygen-sparged fermentation vessel. High volumetric reactor productivities may be achieved by virute of the concentrated stationary cell mass and by the appropriate selection of fiber sizes and materials so as to ensure adequate supplies of liquid and gaseous substrates to, as well as removal of metabolites from, most cells in the culture. This reactor topology is quite general and may be adapted to most microbial as well as mammalian and plant cell systems.     

Increase of Scopolamine Production by High Density Culture of Duboisia myoporoides Roots

A circulation culture system was established for the high density root culture of Duboisia roots. It consists of a vessel for root culture, an aeration tube, a medium reservoir, and a peristaltic pump. Medium saturated with pure oxygen was circulated continuously through the culture vessel and the medium reservoir, and was pumped back into the aeration tube by the pump. Duboisia roots could be cultured at densities of up to 120g dry weight (DW) dm^?3 with no decrease in scopolamine content, this density being about 20 times the amount that can be used in ordinary flask culture. The final scopolamine yield at the end of 3 weeks was 1350mgdm^?3.     

Computational fluid dynamics modeling of mass transfer behavior in a bioreactor for hairy root culture. I. Model development and experimental validation

A two-dimensional axisymmetric computational fluid dynamics (CFD) model based on a porous media model and a discrete population balance model was established to investigate the hydrodynamics and mass transfer behavior in an airlift bioreactor for hairy root culture.During the hairy root culture of Echinacea purpurea, liquid and gas velocity, gas holdup, mass transfer rate, as well as oxygen concentration distribution in the airlift bioreactor were simulated by this CFD model. Simulative results indicated that liquid flow and turbulence played a dominant role in oxygen mass transfer in the growth domain of the hairy root culture. The dissolved oxygen concentration in the hairy root clump increased from the bottom to the top of the bioreactor cultured with the hairy roots, which was verified by the experimental detection of dissolved oxygen concentration in the hairy root clump. This methodology provided insight understanding on the complex system of hairy root culture and will help to eventually guide the bioreactor design and process intensification of large-scale hairy root culture.     

Lateral root bridging as a strategy to enhance L-DOPA production in Stizolobium hassjoo hairy root cultures by using a mesh hindrance mist trickling bioreactor

Stizolobium hassjoo hairy roots exhibited a lateral root bridging behavior, enabling not only root dry weight but enhancement of intracellular L-DOPA content. When a single root tip was exerted a proper hindrance, the primary root growth was inhibited while lateral roots were profusely induced. The hindrance-induced lateral roots from individual primary root could bridge together under appropriate inoculation densities, leading to high density hairy root cultures producing secondary metabolites. In the present paper, a novel bioreactor was proposed based on a strategy of lateral root bridging by utilizing mesh as a hindrance, called "mesh hindrance mist trickling bioreactor (MHMTB)". Significant improvements of dry weight and L-DOPA production by using MHMTB were 1.8 and 2.2-folds, respectively, higher than those in the control run without the mesh hindrance within the root bed.     

Computational fluid dynamics modeling of mass-transfer behavior in a bioreactor for hairy root culture. II. Analysis of ultrasound-intensified process

Recently, cichoric acid production from hairy roots of Echinacea purpurea was significantly improved by ultrasound stimulation in an airlift bioreactor. In this article, the possible mechanism on ultrasound-intensified hairy root culture of E. purpurea in the bioreactor was elucidated with the help of computational fluid dynamics (CFD) simulation, membrane permeability detection, dissolved oxygen concentration detection, confocal laser-scanning microscopy (LSM) observation, and phenylalanine ammonium lyase (PAL) activity analysis. The CFD model developed in Part I was used to simulate the hydrodynamics and oxygen mass transfer in hairy root bioreactor culture stimulated by ultrasound. A dynamic mesh model combined with a changing Schmidt number method was used for the simulation of the ultrasound field. Simulation results and experimental data illustrated that ultrasound intensified oxygen mass transfer in the hairy root clump, which subsequently stimulated root growth and cichoric acid biosynthesis. Ultrasound increased the hairy root membrane permeability, and a high root membrane permeability of 0.359 h(-1) was observed at the bottom region in the bioreactor. LSM observation showed that the change in the membrane permeability recovered to normal in the further culture after ultrasound stimulation. PAL activity in the hairy roots was stimulated by ultrasound increase and was correlated well to cichoric acid accumulation in the hairy roots of E. purpurea.     

Biomass production of hairy roots of Artemisia annua and Arachis hypogaea in a scaled‐up mist bioreactor

Hairy roots have the potential to produce a variety of valuable small and large molecules. The mist reactor is a gas phase bioreactor that has shown promise for low‐cost culture of hairy roots. Using a newer, disposable culture bag, mist reactor performance was studied with two species, Artemisia annua L. and Arachis hypogaea (peanut), at scales from 1 to 20 L. Both species of hairy roots when grown at 1 L in the mist reactor showed growth rates that surpassed that in shake flasks. From the information gleaned at 1 L, Arachis was scaled further to 4 and then 20 L. Misting duty cycle, culture medium flow rate, and timing of when flow rate was increased were varied. In a mist reactor increasing the misting cycle or increasing the medium flow rate are the two alternatives for increased delivery of liquid nutrients to the root bed. Longer misting cycles beyond 2–3 min were generally deemed detrimental to growth. On the other hand, increasing the medium flow rate to the sonic nozzle especially during the exponential phase of root growth (weeks 2–3) was the most important factor for increasing growth rates and biomass yields in the 20 L reactors. A. hypogaea growth in 1 L reactors was µ = 0.173 day^?1 with biomass yield of 12.75 g DW L^?1. This exceeded that in shake flasks at µ = 0.166 day^?1 and 11.10 g DW L^?1. Best growth rate and biomass yield at 20 L was µ = 0.147 and 7.77 g DW L^?1, which was mainly achieved when medium flow rate delivery was increased. The mist deposition model was further evaluated using this newer reactor design and when the apparent thickness of roots (+hairs) was taken into account, the empirical data correlated with model predictions. Together these results establish the most important conditions to explore for future optimization of the mist bioreactor for culture of hairy roots. Biotechnol. Bioeng. 2010;107: 802–813. © 2010 Wiley Periodicals, Inc.     

The scale-up of plant cell culture: Engineering considerations

The enormous versatility of plants has continued to provide the impetus for the development of plant tissue culture as a commercial production strategy for secondary metabolites. Unfortunately problems with slow growth rates and low products yields, which are generally non-growth associated and intracellular, have made plant cell culture-based processes, with a few exceptions, economically unrealistic. Recent developments in reactor design and control, elicitor technology, molecular biology, and consumer demand for natural products, are fuelling a renaissance in plant cell culture as a production strategy. In this review we address the engineering consequences of the unique characteristics of plant cells on the scale-up of plant cell culture.Abbreviations a gas-liquid interfacial area per volume - C dissolved oxygen concentration - C^* liquid phase oxygen concentration in equilibrium with the partial pressure of oxygen in the bulk gas phase - K_L overall mass transfer coefficient - k_L liquid film mass transfer coefficient - m_O2 cell maintenance coefficient for oxygen - OTR oxygen transfer rate - OUR oxygen uptake rate - pO₂ partial pressure of oxygen - STR stirred-tank reactor - v.v.m. volume of gas fed per unit operating volume of reactor per minute - X biomass concentration - Y_x/O2 biomass yield coefficient for oxygen - specific growth rate     

CO2 in large-scale and high-density CHO cell perfusion culture

Productivity in a CHO perfusion culture reactor was maximized when pCO₂ was maintained in the range of 30–76 mm Hg. Higher levels of pCO₂ (> 150 mm Hg) resulted in CHO cell growth inhibition and dramatic reduction in productivity. We measured the oxygen utilization and CO₂ production rates for CHO cells in perfusion culture at 5.55×10^-17 mol cell^-1 sec^-1 and 5.36×10^-17 mol cell^-1 sec^-1 respectively. A simple method to directly measure the mass transfer coefficients for oxygen and carbon dioxide was also developed. For a 500 L bioreactor using pure oxygen sparge at 0.002 VVM from a microporous frit sparger, the overall apparent transfer rates (k_La+k_AA) for oxygen and carbon dioxide were 0.07264 min^-1 and 0.002962 min^-1 respectively. Thus, while a very low flow rate of pure oxygen microbubbles would be adequate to meet oxygen supply requirements for up to 2.1×10⁷ cells/mL, the low CO₂ removal efficiency would limit culture density to only 2.4×10⁶ cells/mL. An additional model was developed to predict the effect of bubble size on oxygen and CO₂ transfer rates. If pure oxygen is used in both the headspace and sparge, then the sparging rate can be minimized by the use of bubbles in the size range of 2–3 mm. For bubbles in this size range, the ratio of oxygen supply to carbon dioxide removal rates is matched to the ratio of metabolic oxygen utilization and carbon dioxide generation rates. Using this strategy in the 500 L reactor, we predict that dissolved oxygen and CO₂ levels can be maintained in the range to support maximum productivity (40% DO, 76 mm Hg pCO₂) for a culture at 10⁷ cells/mL, and with a minimum sparge rate of 0.006 vessel volumes per minute.A = volumetric agitated gas-liquid interfacial area at the top of the liquid, 1/mB = cell broth bleeding rate from the vessel, L/minCER = carbon dioxide evolution rate in the bioreactor, mol/min[CO₂] = dissolved CO₂ concentration in liquid, M[CO₂]^* = CO₂ concentration in equilibrium with sparger gas, M[CO₂]^** = CO₂ concentration in equilibrium with headspace gas, MCO₂(1) = dissolved carbon dioxide molecule in water[C_T] = total carbonic species concentration in bioreactor medium, M[C_T]_F = total carbonic species concentration in feed medium, MD = bioreactor diameter, mD_I = impeller diameter, mD_b = the initial delivered bubble diameter, mF = fresh medium feeding rate, L/minH_L = liquid height in the vessel, mk_A = carbon dioxide transfer coefficient at liquid surface, m/mink _infA ^supO = oxygen transfer coefficient at liquid surface, m/minNomenclature     

Design and characterization of a rotating bed system bioreactor for tissue engineering applications

The main challenge in the development of bioreactors for tissue engineering is the delivery of a sufficient nutrient and oxygen supply for cell growth in a 3D environment. Thus, a new rotating bed system bioreactor for tissue engineering applications was developed. The system consists of a culture vessel as well as an integrated rotating bed of special porous ceramic discs and a process control unit connected with the reactor to ensure optimal culturing conditions. The aim of the project was the design and construction of a fully equipped rotating bed reactor, and in particular, the characterization and optimization of the system with regard to technical parameters such as mixing time and pH-control to guarantee optimal conditions for cell growth and differentiation. Furthermore, the applicability of the developed system was demonstrated by cultivation of osteoblast precursor cells. The porous structure of the ceramic discs and the external medium circulation loop provide an optimal environment for tissue generation in long-term cultivations. Mass transfer limitations were minimized by the slow rotation, which also provides the cells with sufficient nutrients and oxygen through alternate contact to air and medium. An osteoblast precursor cell line was successfully cultivated in this bioreactor for 28 days.     

A comparative study on growth and morphology of wasabi plantlets under the influence of the micro-environment in shoot and root zones during photoautotrophic and photomixotrophic micropropagation

The growth of wasabi (Wasabia japonica Matsumura) plantlets under different micro-environments inside culture vessels in photoautotrophic micropropagation (PA) and photomixotrophic micropropagation (PM) conditions were compared. After 28 days of culture, dry weight, relative growth rate, leaf area, and leaf chlorophyll contents of plantlets in PA were greater than those in PM. The number of leaves did not differ significantly between PA and PM conditions. PA promoted root growth and development with a greater number of roots, root length, root diameter, root fresh weight, root dry weight, and root xylem vessel system. Dissolved oxygen concentration in PA culture medium sharply decreased after 7 days of culture and then recovered. In PM culture medium, no significant fluctuation of dissolved oxygen concentration was apparent. The net photosynthetic rates of plantlets in PA were much higher than those in PM and increased with culture time. In contrast, the net photosynthetic rates of wasabi plantlets in PM kept a low and constant value during the culture period. With the presence of gas exchange membranes attached to the vessel lids, the detected vapor pressure deficit was higher in PA than in PM conditions. Higher stomatal density and larger stomatal aperture on the abaxial and adaxial surfaces of the leaves in PM medium promoted leaf water loss following ex vitro conditions. Thus, PA is applicable for producing healthy wasabi transplants.     

Oxygen requirements and mass transfer in hairy-root culture

Oxygen mass transfer in clumps of Atropa belladonna hairy roots was investigated as a function of root density and external flow conditions. Convection was the dominant mechanism for mass transfer into root clumps 3.5 to 5.0 cm in diameter; Peclet numbers inside the clumps ranged from 1.4 x 10(3) to 7.1 x 10(4) for external superficial flow velocities between 0.4 and 1.4 cm s(-1). Local dissolved-oxygen levels and rates of oxygen uptake were measured in aflow chamber and in bubble column and stirred bioreactors. When air was used as oxygen source, intraclump dissolved-oxygen tensions ranged from90% to 100% air saturation at high external flow velocity andlow root density, to less than 20% air saturation in dense root clumps. Specific oxygen-uptake rate declined with increasing root density. When external boundary layers around individual roots were eliminated byforcing liquid through the clumps at superficial velocities between 0.2 and1.0 cm s(-1), internal dissolved-oxygen tension was maintained at 95% to 100% air saturation and rate of oxygen uptake at 1.6 x 10(-6) g g(-1) s(-1) dry weight. Liquid culture of single A. belladonna hairy roots was used to investigate the effect of dissolved-oxygen tensionon root growth and morphology. Total root length and number of root tips increased exponentially at oxygen tensions between 70% and 100%air saturation. Specific growth rate increased with oxygen tension up to 100% air saturation; this result demonstrates that hairy roots aeratedwithout oxygen supplementation are likely to be oxygenlimited. No growth occurred at 50% air saturation. Growth of hairy roots proceeded with an average length per tip of about 1 cm; this value was essentially independent of dissolved-oxygen tension between 70% and 100% air saturation. (c) 1994 John Wiley & Sons, Inc.     

三相逆流湍动床气液传质性能的研究

由空气-水(清水/废水)-中空玻璃珠构成三相体系,在表观气速0·53~10mm·s-1、固含率为0~0·3、表观液速0~0·2mm·s-1的条件下,采用溶氧仪研究了三相逆流湍动床的气液传质性能,考察了操作参数和液体性质对液相容积传质系数kLa的影响。结果表明,在所试条件下,kLa为0·0456~1·414min-1。kLa随着表观气速和表观液速的增加而增加,随着固含率的增加先增加后减小,0·05~0·08为反应器传质的最优固含率条件。液体性质对kLa有重大影响,高浓度模拟废水和工业废水中的kLa比清水中的kLa分别减小39·0%和50·9%。研究结果可为后续逆流湍动床废水生物处理过程分析与模拟提供传质基础数据。     

Inoculation and tissue distribution in pilot-scale plant root culture bioreactors

Summary Inoculation of large-scale plant root culture reactors can be carried out by briefly homogenizing bulk root tissue, followed by aseptic transfer as a slurry to the reactor. Uniform root distribution can be achieved in bioreactors by entrapment of the growing root inoculum onto process packing elements (e.g. distillation packings), randomly distributed within the reactor, in a bubble column operation. These two techniques have been successfully used to inoculate a 14 L pilot-scale reactor which is subsequently operated as a trickle bed reactor.     

Mass transfer in a rectangular air-lift reactor: effects of geometry and gas recirculation

The interrelationships between the three parts of the air lift reactor, the riser, the downcomer, and gas-liquid separator, were examined with relation to the overall mass transfer in the reactor. This involved studying the mass transfer of oxygen from the gas phase to the liquid phase for 20 different reactor geometries. Both one- and two-sparger systems were studied. It was demonstrated that the gas-liquid separator plays a major role in reactor behavior and must be considered in reactor design. It was found that the overall reactor mass transfer coefficient KLA could be correlated to the pneumatic power of gas input per total dispersion volume (P/VD) and to the true riser superficial gas velocity JGR for all experimental conditions examined. The KLA is directly related to the P/VD with an exponent of approximately 1. "Two-sparger" systems, where an auxiliary gas sparger is placed near the downcomer entrance, have higher ab solute values for KLA than single-sparger systems.     

Production and release of pigments by culture of transformed hairy root of red beet

Adventitious roots were induced from red beet (Beta vulgaris L. cv. Detroit dark red) by infecting the plant with a soil bacterium, Agrobacterium rhizogenes. Based on analysis of opines which are uniquely produced in transformed hairy roots, the established clone was proved to be a transformed hairy root. In a shake culture of the beet hairy root clone with a liquid medium, it was found that significant amounts of pigments, mainly betanin and vulgaxanthin-I, were released into the medium by the cessation of culture shaking (temporary limitation of oxygen supply). The hairy root cells were capable of propagation even after the cells were subjected to shaking cessation. Repeated-batch culture of the beet hairy root was performed with the cell growth phases for 9 or 10 d and with pigment leakage phases during shaking cessation for 2 d, and more than 20% of the total intracellular pigments were recovered from the culture broth at a culture time of 35 d. The released pigments were confirmed to be substantially identical to those extracted from the hairy root and original plant cells of red beet.     

Influence of a propeller on Saccharomyces cerevisiae fermentations in a pilot scale airlift bioreactor

The hydrodynamics (sectional gas holdup and liquid velocities) and oxygen transfer performance of a conventionally operated multiconfigurable pilot scale (0.25?m³) concentric airlift bioreactor containing baker's yeast were significantly improved by operating a marine propeller to draw liquid down the draft tube and aid recirculation at the base of the vessel. Propeller operation reduced the severe DOT heterogeneity of the reactor, which gave DOT values below 1% air saturation in the riser, by producing DOTs above 40% around the vessel at maximum energy dissipation rate. As a consequence the overall oxygen uptake rate (OUR) of the baker's yeast increased up to 3 fold with the total energy dissipation rate into the reactor until the lowest DOTs of the vessel were at or above 10%. The different degrees of heterogeneity generated by the two reactor configurations enabled the reactor to be used as a scale down tool to study the impact of heterogeneity on the physiology of fermentation broths. Comparison of the hydrodynamics and oxygen transfer between tall and short reactor heights revealed that the faster circulation times of the short reactor produced a greater improvement in the OUR with propeller operation even though similar DOT changes occurred around both sizes of reactor. This indicated that the yeast cells were responding to the rapid DOT changes around the vessel.     

The growth of single roots of Artemisia annua in nutrient mist reactors

To better characterize the development and growth of hairy roots in a mist-fed root bed, a single root aerosol reactor was developed. Growth kinetics studies were conducted on hairy roots of Artemisia annua as a function of the mist cycle, carrier gas, and nutrient compositions. Sustained rapid growth was only observed when conditioned medium was fed to the roots. The presence of 1% CO(2) in the carrier gas did not enhance the growth kinetics but it did prevent necrosis of the tissue at the highest mist cycle.