A population balance model to modulate shear for the control of aggregation in Taxus suspension cultures

Abstract

Cellular aggregation in plant suspension cultures directly affects the accumulation of high value products, such as paclitaxel from Taxus. Through application of mechanical shear by repeated, manual pipetting through a 10 ml pipet with a 1.6 mm aperture, the mean aggregate size of a Taxus culture can be reduced without affecting culture growth. When a constant level of mechanical shear was applied over eight generations, the sheared population was maintained at a mean aggregate diameter 194 μm lower than the unsheared control, but the mean aggregate size fluctuated by over 600 μm, indicating unpredictable culture variability. A population balance model was developed to interpret and predict disaggregation dynamics under mechanical shear. Adjustable parameters involved in the breakage frequency function of the population balance model were estimated by nonlinear optimization from experimentally measured size distributions. The optimized model predictions were in strong agreement with measured size distributions. The model was then used to determine the shear requirements to successfully reach a target aggregate size distribution. This model will be utilized in the future to maintain a culture with a constant size distribution with the goal of decreasing culture variability and increasing paclitaxel yields.

Engineering Considerations to Produce Bioactive Compounds from Plant Cell Suspension Culture in Bioreactors

“…One of the most logical and simplest ways to overcome these concerns could be related to the increase in the stirring speed, because it will break the flocs and cell agglomerates, facilitating the substrate and oxygen uptake and, therefore, increasing the growth rate and conversion to desired products [174,181]. Nevertheless, plant cells, as with other micro-organisms, are sensitive to shearing, and surpassing their resistance umbral to hydrodynamic stress may induce their cell wall breakage, causing the loss of valuable products [124,180,182].…”

“…A clear example that the aggregate size is an important parameter for the production of high added-value PDSM is the production of Paclitaxel by Taxus chinensis cultures. The authors of [176,181] showed that mechanical shear helps disintegration, favoring production by having small aggregates (194 µm) compared to the control, in which large aggregates (600 µm) were obtained that directly affected production.…”

The Interface amongst Conserved and Specialized Pathways in Non-Paclitaxel and Paclitaxel Accumulating Taxus Cultures

“…Furthermore, the taxane and phenylpropanoid biosynthetic pathways could be separately co-regulated by factors outside of methyl jasmonate elicitation, which would explain their unique responses with respect to aggregate size. It was recently reported that shear forces can be used to decrease aggregate size in a predictable and controlled manner, providing opportunity to further engineer the Taxus production system [30]. Application of this technique with transcriptomic analysis could provide a method to further understand the effect of elicitation state and aggregate size especially in pathways other than taxane biosynthesis.…”