Prolonged shearing of insect cells in a couette bioreactor

A unique phenotypic modification of Lactococcus lactis cultivated in a Couette bioreactor

Batch cultures of Lactococcus lactis NCDO 2118 and IL 1403 were performed in a Couette bioreactor operated in the modulated wavy vortex flow and the turbulent regimes. This study provides an overall analysis taking into account both mechanical stress and mixing in a Couette bioreactor. A unique phenotypic aspect has been proved to occur only in the modulated wavy vortex flow regime for the two studied strains, namely that the cells become entrapped in a filamentous form. No change in the metabolic behavior of the cells has been observed. The polymeric matrix has been microscopically observed through FISH and fluorescent lectin binding, showing cells entrapped in a glycoconjugate matrix. All hypotheses regarding insufficient mixing as a cause of this phenotype have been discarded, leading to the conclusion that this particular phenotypic feature is essentially due a combined effect of mechanical stress and flow structure. Particle size measurement during the fermentation course indicates that formation of filamentous form results from a continuous aggregation started in the early stages of the cultivation. According to our results a minimum shear is required to induce the ability for cells to aggregate. Then, it appears that both flow structure and mechanical stress (shear) are responsible for the appearance of such a filamentous form. As far as the authors know, this is the first experimental evidence of a bio polymerization induced by the flow structure.

Effects of shear stress on the microalgae Chaetoceros muelleri

The effect of shear stress on the viability of Chaetoceros muelleri was studied using a combination of a rheometer and dedicated shearing devices. Different levels of shear stress were applied by varying the shear rates and the medium viscosities. It was possible to quantify the effect of shear stress over a wide range, whilst preserving laminar flow conditions through the use of a thickening agent. The threshold value at which the viability of algae was negatively influenced was between 1 and 1.3 Pa. Beyond the threshold value the viability decreased suddenly to values between 52 and 66%. The effect of shear stress was almost time independent compared to normal microalgae cultivation times. The main shear stress effect was obtained within 1 min, with a secondary effect of up to 8 min.

Modeling suppression of cell death by Bcl-2 over-expression in myeloma NS0 6A1 cells

A novel population-balance model was employed to evaluate the suppression of cell death in myeloma NS0 6A1 cells metabolically engineered to over-express the apoptotic suppressor Bcl-2. The model is robust in its ability to simulate cell population dynamics in batch suspension culture and in response to thymidine-induced growth inhibition: 89% of simulated cell concentrations are within two standard deviations of experimental data. Kinetic rate constants in model equations suggest that Bcl-2 over-expression extends culture longevity from 6 days to at least 15 days by suppressing the specific rate of early apoptotic cell formation by more than 6-fold and necrotic cell formation by at least 3-fold, despite nearly a 3-fold decrease in initial cell growth rate and no significant change in the specific rate of late apoptotic cell formation. This computational analysis supports a mechanism in which Bcl-2 is a common mediator of early apoptotic and necrotic events occurring at rates that are dependent on cellular factors accumulating over time. The model has current application to the rational design of cell cultures through metabolic engineering for the industrial production of biopharmaceuticals.

Protein response of insect cells to bioreactor environmental stresses

Protein expression of Spodoptera frugiperda (Sf9) insect cells was characterized upon exposure to environmental stresses typically present in bioreactors including heat shock, oxygen deprivation, shear stress, change of pH, and salinity or ethanol shock. This study fills the void in knowledge as to how bioreactor hydrodynamics, anoxia, small changes in pH as well as salinity alterations due to pH control or exposure to ethanol used in asepsis treatments affect protein expression in Sf9 cells. Heat shock at 43 degrees C induced proteins at 83 kDa, 68-78 kDa and six small heat shock proteins (hsps) at 23-15.5 kDa. Anaerobic conditions in CO2 atmosphere reduced significantly the normal protein synthesis and induced a small subset of heat shock proteins at 70 kDa. Oxygen deprivation in nitrogen atmosphere transiently induces the 70 kDa proteins and had minor effects on the normal protein synthesis. Exposure to increased salinity or ethanol concentration failed to trigger the stress response, but may extensively inhibit the induction of normal proteins even though there was a negligible change in cell viability. Shear stress that had a major reducing effect on cell viability did not change the protein synthesis profile of Sf9 cells. Both long and short term exposures to small pH changes had negligible effects on protein synthesis.