Reduction In Cell Concentration Research Articles

Forced degradation of cell-based medicinal products guided by flow imaging microscopy: Explorative studies with Jurkat cells

Cell-based medicinal products (CBMPs) offer ground-breaking opportunities to treat diseases with limited or no therapeutic options. However, the intrinsic complexity of CBMPs results in great challenges with respect to analytical characterization and stability assessment. In our study, we submitted Jurkat cell suspensions to forced degradation studies mimicking conditions to which CBMPs might be exposed from procurement of cells to administration of the product. Flow imaging microscopy assisted by machine learning was applied for determination of cell viability and concentration, and quantification of debris particles. Additionally, orthogonal cell characterization techniques were used. Thawing of cells at 5 °C was detrimental to cell viability and resulted in high numbers of debris particles, in contrast to thawing at 37 °C or 20 °C which resulted in better stability. After freezing of cell suspensions at −18 °C in presence of dimethyl sulfoxide (DMSO), a DMSO concentration of 2.5% (v/v) showed low stabilizing properties, whereas 5% or 10% was protective. Horizontal shaking of cell suspensions did not affect cell viability, but led to a reduction in cell concentration. Fetal bovine serum (10% [v/v]) protected the cells during shaking. In conclusion, forced degradation studies with application of orthogonal analytical characterization methods allow for CBMP stability assessment and formulation screening.

Cytotoxic effect of cipó-pucá (Cissus sicyoides L.) supercritical extract on human red blood cells and as anti-inflammatory in spinal cord injury in adult rats

Cissus sicyoides L. is a plant that has great anti-inflammatory activity, due to the presence of phenolic compounds. The objective of this work was to identify such substances by HPLC and to evaluate the cytotoxic effect on human red blood cells, of the C. sicyoides extract obtained by supercritical extraction, using CO2 and EtOH as co-solvent, in comparison to the extract obtained by conventional extraction (Soxhlet), as well as, to evaluate its anti-inflammatory effect on spinal cord injury (SCI) in adult rats. In HPLC analysis, the UV/Visible spectral data revealed compounds with absorption bands in wavelengths characteristic of glycosylated flavonoids. The supercritical extract did not show cytotoxic effect, as there was no rupture of red blood cell membranes. The in vivo test demonstrated reduction in cell concentration in the lesion surrounding area in treated animals, suggesting an anti-inflammatory effect of the supercritical extract on the SCI model.

Karmitoxin production by Karlodinium armiger and the effects of K. armiger and karmitoxin towards fish

The dinoflagellate Karlodinium armiger has a huge impact on wild and caged fish during blooms in coastal waters. Recently, a new toxin, karmitoxin, was chemically characterized from K. armiger and a quantification method was established, thereby allowing investigations of the fish killing mechanism. K. armiger is not able to grow in standard growth media that are based on nitrate as a nitrogen source, and successful cultures of this species have only been achieved in mixotrophic cultures after addition of a prey source. Here we show that addition of ammonium (up to 50 µM) to the growth media is a good alternative, as K. armiger batch cultures achieve growth rates, which are comparable to growth rates reached in mixotrophic cultures. Karmitoxin production (1.9 and 2.9 pg cell−1 d−1) and cellular karmitoxin content (8.72 ± 0.25 pg cell−1 and 7.14 ± 0.29 pg cell−1) were in the same range, though significantly different, in prey-fed cultures and monocultures supplied with ammonium, respectively. Net production of karmitoxin stopped when the K. armiger cultures reached stationary growth phase, indicating no accumulation of karmitoxin in cells or growth media. Toxicity tests towards sheepshead minnow fish larvae indicated rapid death of the fish larvae when exposed to high K. armiger cell concentrations (LT50 of 2.06 h at 44.9 × 103 cells mL−1 cultivated with ammonium). Purified toxins caused the same physical damage to fish larvae as living K. armiger cultures. An exposure of purified karmitoxin to fish larvae and rainbow trout gill cells indicated that the fish larvae were about three times less sensitive than gill cells. When comparing the effect of purified toxins with the effect of whole K. armiger cultures, twice the toxin concentration of the purified toxins was needed to cause the same effect. Although a loss of karmitoxin of twenty percent was observed during the incubation, this could not explain the apparent discrepancy. Other factors, like a direct effect of the K. armiger cells on the fish larvae or other, yet unknown toxins may influence the effect of whole cell cultures. To study the effects of released karmitoxin, fish larvae were exposed to a K. armiger culture that was treated with HP-20 resin, which adsorbs extracellular karmitoxin. The 24 h HP-20 treatment resulted in a K. armiger culture that had 37% less total karmitoxin, without a reduction in cell concentration, and a reduced toxic effect was observed in the HP-20 treated culture, as compared to non-treated controls. Fish larvae that were exposed to HP-20 treated culture were immobilized, but survived during the 12 h exposure, whereas the exposure to non-treated culture led to high mortality of the fish larvae. Direct observations under the microscope revealed no evidence of micropredation of K. armiger on the fish larvae during any of the exposures. Thus, the results presented here, indicate that released karmitoxin is the main cause for fish kills by K. armiger. Finally, we found that juvenile rainbow trout were six times more sensitive than fish larvae towards K. armiger, indicating that juvenile fish are more sensitive to K. armiger in bloom situations than early larval stages.

Acute growth inhibition & toxicity analysis of nano-polystyrene spheres on Raphidocelis subcapitata

Micro/nano-plastics (MNPs) have been found within many environments and organisms including humans, making them a significant and growing concern. Initial research into the potential detrimental effects these MNPs both from acute and chronic exposure has been ongoing but still requires substantially more data to clarify. This research presents the response of nano-polystyrene (NPS) on Raphidocelis subcapitata, a freshwater alga, under an existing acute toxicity test along with additional analytical techniques to try identifying possible sources of toxicity. R. subcapitata cells were exposed for 72 h to a concentration range of 0–100 mg/l NPS. Growth Inhibition (GI) testing showed the R. subcapitata demonstrated statistically distinct reductions in growth over 72 h at all NPS exposure concentrations while not suffering culture collapse. By the 100 mg/l NPS exposure the R. subcapitata has suffered almost a 33.7% reduction in cell concentration after 72 h compared to control samples. Confocal imaging showed the NPS wasn't permeating into the algal plasma membrane or individual organelles but agglomerated onto the algal cell wall. The agglomeration was irregular but increased in total surface area covered as NPS concentration increases. UV–Vis fluorimetry testing produced a linear response of emission intensities to algae exposed to the 0–100 mg/l range of NPS. However, comparisons of emission intensity values of algae exposed to NPS to emission intensities of pure NPS at identical concentrations showed consistent intensity reduction. This response further indicated NPS agglomerating within the media and onto the alga cells seen from confocal imaging. Finally, Raman spectroscopy on R. subcapitata attempted to distinguish the key 1001 cm−1 peak or other crucial identifier peaks of polystyrene from overall Raman spectra. This was not successful as emissions from algal component (e.g. phenylaniline) completely suppressed the signal region.

Bacteriophages Infecting Gram-Negative Bacteria in a Commercial Cucumber Fermentation

Cucumber fermentations are one of the most important vegetable fermentations in the United States. The fermentation is usually driven by lactic acid bacteria (LAB) indigenous to fresh cucumbers. But LAB are greatly outnumbered by many Gram-negative bacteria on fresh cucumbers, which may influence the growth of LAB and the incidence of bloater defect (hollow cavities formed inside fermented cucumbers) leading to serious economic loss to the pickle industry. Rapid elimination of Gram-negative bacteria is crucial to the dominance of LAB and the reduction of bloater defect in the fermentation. Various factors can affect the viability of Gram-negative bacteria in cucumber fermentation. Bacteriophages (phages) may be one of such factors. This study explored the abundance, diversity, and functional role of phages infecting Gram-negative bacteria in a commercial cucumber fermentation. Cover brine samples were taken from a commercial fermentation tank over a 30-day period. On day 1 and day 3 of the fermentation, 39 Gram-negative bacteria and 26 independent phages were isolated. Nearly 67% of Gram-negative bacterial isolates were susceptible to phage infection. Phage hosts include Enterobacter, Citrobacter, Escherichia, Pantoea, Serratia, Leclercia, Providencia, and Pseudomonas species. About 88% of the isolated phages infected the members in the family Enterobacteriaceae and 58% of phages infected Enterobacter species. Eight phages with unique host ranges were characterized. These phages belong to the Myoviridae, Siphoviridae, or Podoviridae family and showed distinct protein profiles and DNA fingerprints. The infectivity of a phage against Enterobacter cancerogenus was evaluated in cucumber juice as a model system. The phage infection at the multiplicity of infection 1 or 100 resulted in a 5-log reduction in cell concentration within 3 h and rapidly eliminated its host. This study revealed the abundance and variety of phages infecting Gram-negative bacteria, particularly Enterobacteriaceae, in the commercial cucumber fermentation, suggesting that phages may play an important role in the elimination of Gram-negative bacteria, thereby facilitating the dominance of LAB and minimizing bloater defect. To our knowledge, this is the first report on the ecology of phages infecting Gram-negative bacteria in commercial cucumber fermentations.

Escherichia coli O157:H7 bacteriophage Φ241 isolated from an industrial cucumber fermentation at high acidity and salinity.

A novel phage, Φ241, specific for Escherichia coli O157:H7 was isolated from an industrial cucumber fermentation where both acidity (pH ≤ 3.7) and salinity (≥5% NaCl) were high. The phage belongs to the Myoviridae family. Its latent period was 15 min and average burst size was 53 phage particles per infected cell. The phage was able to lyse 48 E. coli O157:H7 strains, but none of the 18 non-O157 strains (including E. coli O104:H7) or the 2 O antigen-negative mutants of O157:H7 strain, 43895Δper (also lacking H7 antigen) and F12 (still expressing H7 antigen). However, the phage was able to lyse a per-complemented strain (43895ΔperComp) which expresses O157 antigen. These results indicated that phage Φ241 is specific for O157 antigen, and E. coli strains lacking O157 antigen were resistant to the phage infection, regardless of the presence or absence of H7 antigen. SDS-PAGE profile revealed at least 13 structural proteins of the phage. The phage DNA was resistant to many commonly used restriction endonucleases, suggesting the presence of modified nucleotides in the phage genome. At the multiplicity of infection of 10, 3, or 0.3, the phage caused a rapid cell lysis within 1 or 2 h, resulting in 3.5- or 4.5-log-unit reduction in cell concentration. The high lytic activity, specificity and tolerance to low pH and high salinity make phage Φ241 a potentially ideal biocontrol agent of E. coli O157:H7 in various foods. To our knowledge, this is the first report on E. coli O157:H7 phage isolated from high acidity and salinity environment.

Impact of procedural steps and cryopreservation agents in the cryopreservation of chlorophyte microalgae.

The maintenance of traditional microalgae collections based on liquid and solid media is labour intensive, costly and subject to contamination and genetic drift. Cryopreservation is therefore the method of choice for the maintenance of microalgae culture collections, but success is limited for many species. Although the mechanisms underlying cryopreservation are understood in general, many technical variations are present in the literature and the impact of these are not always elaborated. This study describes two-step cryopreservation processes in which 3 microalgae strains representing different cell sizes were subjected to various experimental approaches to cryopreservation, the aim being to investigate mechanistic factors affecting cell viability. Sucrose and dimethyl sulfoxide (DMSO) were used as cryoprotectants. They were found to have a synergistic effect in the recovery of cryopreserved samples of many algal strains, with 6.5% being the optimum DMSO concentration. The effect of sucrose was shown to be due to improved cell survival and recovery after thawing by comparing the effect of sucrose on cell viability before or after cryopreservation. Additional factors with a beneficial effect on recovery were the elimination of centrifugation steps (minimizing cell damage), the reduction of cell concentration (which is proposed to reduce the generation of toxic cell wall components) and the use of low light levels during the recovery phase (proposed to reduce photooxidative damage). The use of the best conditions for each of these variables yielded an improved protocol which allowed the recovery and subsequent improved culture viability of a further 16 randomly chosen microalgae strains. These isolates included species from Chlorellaceae, Palmellaceae, Tetrasporaceae, Palmellopsis, Scenedesmaceae and Chlamydomonadaceae that differed greatly in cell diameter (3–50 µm), a variable that can affect cryopreservation success. The collective improvement of each of these parameters yielded a cryopreservation protocol that can be applied to a broad range of microalgae.

Sensitivity ofMycobacterium aviumsubspparatuberculosis,Escherichia coliandSalmonella entericaserotype Typhimurium to low pH, high organic acids and ensiling

To evaluate the persistence of Mycobacterium avium subsp paratuberculosis (Myco. paratuberculosis), Salmonella enterica serotype Typhimurium (Salm.Typhimurium) and a commensal Escherichia coli (E. coli) isolate under the low pH and high organic acid (OA) conditions of ensiling of forages. Decay rates and the time required to obtain a 90% reduction in cell concentration were calculated following (i) exposure to buffered OA (pH 4.0, 5.0, 6.0 or 7.0) (ii) exposure to silage exudates and (iii) survival through ensiling of forage materials. Salm. Typhimurium had higher decay rates in silage exudates (-0.5601 day(-1) ) than did E. coli (-0.1265 day(-1) ), but both exhibited lower decay rates in silage than in OA or silage exudates. Myco. paratuberculosis showed no decrease in silage and decay rates in silage exudates were significantly lower (2-12 times) than for the other two organisms. Escherichia coli, Salm. Typhimurium and Myco. paratuberculosis exhibit marked differences in response to acidity. All three organisms show acid resistance, but Myco. paratuberculosis in particular, if present in manure and applied to forage grasses, may survive the low pH and high OA of the ensilaging process; silage may therefore be a potential route of infection if ingested by a susceptible animal. This information contributes to the understanding of potential risks associated with silage preservation and contamination of livestock feed with manure-borne pathogens.

Role of insulin hormone in modulation of inflammatory phenomena.

Evidence demonstrates the involvement of hormones in the development of inflammatory response. Inflammation evokes marked structural alterations of microvasculature, besides migration of leukocytes from microcirculation to the site of lesion. These alterations are caused primarily by release or activation of endogenous mediators, in which hormones play an integral role in this regulatory system. Binding sites for many hormones may be characterized by vascular structures and hematogenous cells involved with the inflammatory response. Quantitative alterations of inflammatory events involving the decrease in microvascular response to inflammatory mediators, deficiency in the leukocyte-endothelium interaction, reduction of cell concentration in the inflammatory exudate, and failure of the phagocyte function of mononuclear cells were observed in insulin- deficient states. Therefore, inflammation is not merely a local response, but rather a process controlled by hormones in which insulin plays an essential role in modulation of these phenomena, and assures tissue repair and remodeling within the limits of normality.

Hydrophobic bacteria at the hexadecane–water interface: Examination of micrometre-scale interfacial properties

Hydrophobic bacteria, like colloidal solids, can spontaneously adsorb onto fluid–fluid interfaces and modify their mechanical properties. In this study, two strains of bacteria – Acinetobacter venetianus RAG-1 and Rhodococcus erythropolis 20S-E1-c – were prepared in their stationary (i.e. non-dividing) phase in the absence of biosurfactants; the cells were then used as emulsifiers to stabilize n-hexadecane droplets in aqueous environments. Using the micropipette technique, colloidal stability of the bacteria-coated droplets was examined through direct-contact experiments. Both types of bacteria were seen to function as effective stabilizers, although the Acinetobacter venetianus RAG-1 film provided stronger resistance to droplet–droplet coalescence. In addition to creating steric barriers, the adsorbed bacteria also interacted with one another at the interface, giving rise to higher order rheological properties. A technique of directly probing the mechanical properties of the emulsion drop surfaces (i.e. the adsorbed films) on the micrometre-scale revealed that (a) the films behaved as purely elastic sheets, and (b) with a reduction in cell concentration in the aqueous phase, less oil was emulsified, but the elastic moduli of the adsorbed films remained unchanged (suggesting an “all or none” adsorption process). These results are in contrast to a previous macroscopic (i.e. millimetre-scale) study, which showed that the absorbed films were viscoelastic, with the apparent elastic moduli depending strongly on cell concentration. The rheological properties of these bacteria-adsorbed interfaces appeared therefore to be length scale-dependent.

Enhanced adsorption of zinc is associated with aging and lysis of bacterial cells in batch incubations

Bacteria can immobilize significant quantities of trace metals through surface complexation reactions. However, bacterial cell lysis is an integral part of the development process, and the extent to which this process affects adsorbed metals has not been properly investigated. In order to evaluate the effects of cell lysis on metal fixation, bacterial suspensions containing approximately 10 ppm Zn in 0.01 M NaNO(3) were monitored over an one-month period for adsorbed Zn, pH, cell concentration, dissolved organic carbon, NH(3) and dissolved amino acids. Cell concentration decreased with time, in parallel with an increase in dissolved organic carbon. Zn adsorption decreased with time for suspensions with near-neutral (5.5-7.0) initial pH values, consistent with the reduction in cell concentration and/or formation of metal-ligand complexes in solution, with lysis products acting as ligands. However, Zn adsorption increased with time for suspensions with initially low pH (<or=5), and was accompanied by an upward shift in suspension pH. Surface complexation modelling suggests that enhanced adsorption of Zn is predominantly due to the increase in pH, with ternary surface complexation at pH values below the pK(a) of the carboxyl surface sites. The increase in pH is due to production of ammonia, and/or proton buffering by the amphoteric cytoplasmic compounds. The observed changes may have implications for understanding metal sequestration during remineralisation of organic matter in nature.

Effect of Age and Sampling Site on the Chondro-Osteogenic Potential of Rabbit Marrow-derived Mesenchymal Progenitor Cells

Four sequential bone-marrow aspirations from the ipsilateral tibia and iliac crest of New Zealand White rabbits, aged 4 months or 1, 2, or 3 years, were assayed in vitro and in vivo for their chondro-osteogenic potential. Nonhematopoietic cells from the samples of bone marrow were isolated and expanded in culture; their colony-forming efficiency was determined, and second-passage marrow-derived cells, referred to as mesenchymal progenitor cells, were loaded into porous calcium-phosphate ceramic cubes as carrier vehicles for an in vivo cartilage and bone-formation assay. The cubes were placed subcutaneously in nude BALB/C mice for 3 and 6 weeks. On histological examination, the cubes were scored for the presence of bone and cartilage in their pores, and average values for age groups and location were compared. At aspiration, the samples from the iliac crest exhibited an overall reduction in cell concentration with increasing age, and at the first harvest time, they showed a decrease in colony-forming efficiency and cube score with increasing age. This study demonstrated that repeated bone-marrow aspirations may be performed and may have an enhancing effect on the osteochondral progenitor cells of older animals.

Effect of age and sampling site on the chondro-osteogenic potential of rabbit marrow-derived mesenchymal progenitor cells.

Four sequential bone-marrow aspirations from the ipsilateral tibia and iliac crest of New Zealand White rabbits, aged 4 months or 1, 2, or 3 years, were assayed in vitro and in vivo for their chondro-osteogenic potential. Nonhematopoietic cells from the samples of bone marrow were isolated and expanded in culture; their colony-forming efficiency was determined, and second-passage marrow-derived cells, referred to as mesenchymal progenitor cells, were loaded into porous calcium-phosphate ceramic cubes as carrier vehicles for an in vivo cartilage and bone-formation assay. The cubes were placed subcutaneously in nude BALB/C mice for 3 and 6 weeks. On histological examination, the cubes were scored for the presence of bone and cartilage in their pores, and average values for age groups and location were compared. At aspiration, the samples from the iliac crest exhibited an overall reduction in cell concentration with increasing age, and at the first harvest time, they showed a decrease in colony-forming efficiency and cube score with increasing age. This study demonstrated that repeated bone-marrow aspirations may be performed and may have an enhancing effect on the osteochondral progenitor cells of older animals.

Enhancing bacterial transport for bioaugmentation of aquifers using low ionic strength solutions and surfactants

The transport of bacteria in contaminated aquifers over a distance of only one meter can require tens to thousands of unsuccessful collisions of bacteria with soil grains. Previous work has shown that low ionic strength (IS) solutions and the nonionic surfactant Tween 20 can reduce bacterial adhesion to ultraclean surfaces such as glass and quartz porous media. In this study, we examined whether these results could be generalized to soils and to other surfactants, by measuring the retention of two species of radiolabeled microbes over short (1 cm) distances in soil minicolumns. Calculations were also made, using the clean-bed filtration theory, to evaluate if bacterial transport distances are sufficient for bioagumentation to occur over a large region of the subsurface. Collision efficiencies were expressed using the filtration model in terms of the sticking coefficient, α, defined as the fraction of collisions that are successful. In glass bead columns, α's for monoclonal populations were reduced from α=0.19 ( Alcaligenes paradoxus) and α=0.01 (CD1), to α<0.008 for Tween 80-phosphate buffer solutions and α<0.0054 for low ionic strength (0.01 mM) solutions (Darcy velocity, U=10 −3 m s −1; Hammaker constant=10 −20 J; and fluid properties of water at 22°C). Low α's were also obtained using other nonionic surfactants (Tween 80, Triton 100 and 705, POE-10, Brij+35) and an anionic biosurfactant, all added at concentrations above their critical micelle concentration (CMC). Although sticking coefficients were also reduced by an order-of-magnitude for natural soils, sticking coefficients remained too high to permit wide dispersal of cells over distances of >1 m. For A. paradoxus, α was reduced using a low ionic strength solution from 0.72 to 0.083 for the Arizona soil and from 1.7 to 0.2 for the Ringold soil; for CD1, α was reduced from 0.57 to 0.09 for the Ringold soil. Based on the soil grain diameters of these soils (127 μm, Arizona soil; 224 μm, Ringold soil), α's in this range will permit transport distances (defined as 99.9% reduction in cell concentration) of ∼1 m ( U=10 m/d, 10°C) which may be sufficient for creating small, bioactive zones. However, in order to increase bacterial transport over distances >1 m, methods other than simple solution chemistry changes will be needed to enhance aquifer bioaugmentation operations.

Lead distribution in a simulated aquatic environment: Effects of bacterial biofilms and iron oxide

Biofilms influence the transport and fate of heavy metals in aquatic environments both directly by adsorption and complexation reactions and indirectly via interactions with oxides of iron and manganese. These reactions were investigated by introducing lead into a continuous-flow biofilm reactor that was designed to simulate conditions in a flowing freshwater aquatic environment. The reactor provided controlled conditions, and use of a chemically-defined growth medium allowed calculation of lead speciation with a chemical equilibrium program (MINEQL). Pseudomonas cepacia was employed as a test cell strain because of its ability to grow and form biofilms in the defined medium. This bacterium affected lead distribution in the reactor by adsorbing lead both to adherent and suspended cells. When the aqueous bulk lead concentration was 1.4 ± 0.1 μM and biofilm coverage (measured as chemical oxygen demand, COD) was 50 mequiv COD/m 2, lead adsorption was increased by about a factor of five relative to bare glass. Of the total lead in solution, only 1% was adsorbed to suspended cells (5 × 10 7 cells/ml). Lead adsorption to biofilms followed a Langmuir isotherm with a maximum adsorption ( Γ max) of 56 μmol Pb/equiv COD and an adsorption equilibrium constant ( K) of 0.64 liter/μmol Pb. Lead complexed with dissolved bacterial expopolymer was below detection limits. Pretreatment of glass slides with colloidal iron also significantly increased lead adsorption relative to bare glass. Lead adsorption to adsorbed iron fit a Langmuir isotherm with Γ max = 50 μmol Pb/mol fe, and K = 1.3 liter/μmol Pb. Lead binding to glass coated with both cells and iron was additive, and could be predicted by summing adsorption predicted using isotherms for each constituent. The presence of iron surface coatings increased initial biofilm formation rates, but after reaching steady state conditions, biofilm coverage was similar for slides treated with iron and untreated slides. A concentration of 1 μM lead produced a transient reduction in suspended cell counts. Cell counts recovered to the original cell density over the course of five to ten reactor retention times. With iron present, the magnitude of the reduction in cell concentration in response to the addition of lead was greatly reduced, suggesting that toxic effects of lead may be reduced by iron.

Effects of rheological properties and mass transfer on plant cell bioreactor performance: Production of tropane alkaloids

Volumetric mass transfer coefficients, K(L)a were measured over an aeration rate range from 0.1 to 1.0 vvm in a 1.2-L draft-tube-type airlift bioreactor for different Datura stramonium cell concentrations and correlated with superficial air velocity and rheological properties of the cell suspension. The measured K(L)a values (17-40 h(-1)) for a cell volume fraction of 0.2 (v/v) were approximately 2 times higher than those for the highest cell concentrations tested (cell volume fraction 0.7-0.8 v/v). Cell suspensions exhibited yield stress and pseudoplastic behavior. This behavior was described by the Casson model. The estimated yield stress values depended upon cell concentration with an exponent of 4.0. An empirical correlation based on the data for plant cell suspensions exhibiting yield stress was developed in order to determine aeration strategy for the plant cell cultivation in draft-tube-type airlift bioreactors: K(L)a = A(U(gr))(0.3(eta(eff))(-0.4). Aeration rates above 1.0 vvm caused a significant drop in cell yield and product content. Maximum growth and production were obtained at 0.6 vvm aeration. The cell and product yields obtained at 1.7 vvm were 2.8 times lower than the maximum values (25 g cell DW/L and 73.8 mg tropane alkaloid/L). The effects of the increased aeration rates on cell yield were also evaluated in terms of Reynolds stress. It was found that there was a relation between cell damage and the estimated Reynolds stress. The Reynolds stress estimated for the same aeration rate decreased with increasing cell concentration, suggesting that cells in the cultures at low cell concentrations are subjected to hydrodynamic damage. In the experiments with the cell cultures having a cell concentration of 0.3 (v/v), approximately 70% reduction in cell concentration was observed when the Reynolds stress was increased from 10 to 50 dyn/cm(2).