The role of liquid mixing and gas-phase dispersion in a submerged, sparged root reactor

Self Cite

Trickle-bed root culture reactors are shown to achieve tissue concentrations as high as 36 g DW/L (752 g FW/L) at a scale of 14 L. Root growth rate in a 1.6-L reactor configuration with improved operational conditions is shown to be indistinguishable from the laboratory-scale benchmark, the shaker flask (mu=0.33 day(-1)). These results demonstrate that trickle-bed reactor systems can sustain tissue concentrations, growth rates and volumetric biomass productivities substantially higher than other reported bioreactor configurations. Mass transfer and fluid dynamics are characterized in trickle-bed root reactors to identify appropriate operating conditions and scale-up criteria. Root tissue respiration goes through a minimum with increasing liquid flow, which is qualitatively consistent with traditional trickle-bed performance. However, liquid hold-up is much higher than traditional trickle-beds and alternative correlations based on liquid hold-up per unit tissue mass are required to account for large changes in biomass volume fraction. Bioreactor characterization is sufficient to carry out preliminary design calculations that indicate scale-up feasibility to at least 10,000 liters.

Section: Estimation Of Bioreactor Solid -Liquid Mass Transfer Coefficmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Trickle‐bed root culture bioreactor design and scale‐up: Growth, fluid‐dynamics, and oxygen mass transfer

Ramakrishnan

Curtis

2004

Self Cite

“…Oxygen is often the most difficult nutrient to deliver to cells (Taticek et al, 1990) due to its low solubility in water and the difficulty in transferring oxygen across the hydrodynamic boundary layer (Kanokwaree and Doran, 1998;KinoOka et al, 1996;Tescione et al, 1997;Williams and Doran, 1999). To better understand the oxygen requirements for our root clone, we determined the actual yield of biomass from oxygen YЈ X/O 2 and the maintenance coefficient for oxygen m O 2 from the relationship between the specific growth rate and the specific O 2 consumption rate given by…”

Section: Respiration Rates In Bubble Column Reactorsmentioning

confidence: 99%

“…Because water is taken up by the tissues and lost by evaporation, the volume of medium in the reactor is not constant. Thus, a more robust way to estimate biomass accumulation is to measure the decrease in nutrient mass rather than the decrease in nutrient concentration (Jung et al, 1998;Ramakrishnan et al, 1999;Tescione et al, 1997). A more general equation is…”

Section: Appendix Correlating Biomass Increase With Nutrient Consumptionmentioning

confidence: 99%

Growth dynamics of Artemisia annua hairy roots in three culture systems

Kim

Weathers

Wyslouzil

2003

The transient growth of Artemisia annua hairy roots was compared for cultures grown in shake flasks and in bubble column and mist reactors. Instantaneous growth rates were obtained by numerically differentiating the transient biomass measurements. Specific sugar consumption rates showed good agreement with literature values. From the growth rate and sugar consumption rate, the specific yield and maintenance coefficient for sugar were determined for all three culture systems. These values were statistically indistinguishable for roots grown in shake flasks and bubble columns. In contrast, the values for roots grown in bubble columns and mist reactors were statistically different, suggesting that sugar utilization by roots grown in these two systems may be different. By measuring respiration rates in the bubble column reactor we also determined the actual biomass yield and maintenance coefficient for O(2) and CO(2). Together with an elemental analysis of the roots, this allowed us to obtain a reasonable carbon balance.

“…Several studies have shown that oxygen transfer is poor in root cultures submerged in liquid medium (McKelvey et al, 1993;Tescione et al, 1997;Weathers et al, 1999;Williams and Doran, 2000;Yu and Doran, 1994), primarily because mixing must be restricted to prevent shear damage to the tissues. Various aspects of root morphology such as diameter, branchedness, and rigidity (Carvalho et al, 1997) and the proli®cacy and length of the root hairs (Bordonaro and Curtis, 2000;Shiao and Doran, 2000) can aect¯uid¯ow resistance, and therefore external oxygen transfer, in hairy root cultures.…”

Section: Introductionmentioning

confidence: 99%

Overexpression of alcohol dehydrogenase or pyruvate decarboxylase improves growth of hairy roots at reduced oxygen concentrations

Shiao

Ellis

Dolferus

et al. 2002

Overexpression of Arabidopsis thaliana genes for the fermentation enzymes, alcohol dehydrogenase and pyruvate decarboxylase, improved the tolerance of A. thaliana hairy roots to low oxygen conditions. Whereas the specific growth rate of untransformed hairy roots in shake flasks and in a multiple-tube recirculation bioreactor declined significantly with decreasing oxygen tension down to 25% air saturation, growth of the transformant root lines was maintained at rates similar to those achieved with full aeration. This work demonstrates that altering the expression of selected genes involved in anaerobic metabolism can alleviate the problems of oxygen deficiency in hairy root cultures caused by poor mixing and mass transfer conditions.