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Live Cell Analysis of Shear Stress on Pseudomonas aeruginosa Using an Automated Higher-Throughput Microfluidic System

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Average shear rate in three pneumatic bioreactors.

Sérgio S Thomasi¹, Marcel O Cerri, Alberto C Badino

¹Department of Chemical Engineering, Federal University of S. Carlos, CP 676, São Carlos, SP, CEP 13565-905, Brazil.

Bioprocess and Biosystems Engineering

|April 7, 2010

Summary

This study assessed average shear rate (γav) in pneumatic bioreactors using a novel method. Bubble column bioreactors showed the lowest shear, while concentric-tube airlift bioreactors exhibited the highest, impacting microbial cell structure.

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Area of Science:

Biochemical Engineering
Fluid Dynamics
Bioprocess Technology

Background:

Shear stress in bioreactors can impact microbial physiology and productivity.
Accurate assessment of shear rate is crucial for optimizing bioprocesses.
Pneumatic bioreactors offer advantages in gas-liquid mass transfer but can induce significant shear.

Purpose of the Study:

To evaluate the average shear rate (γav) in three different 5-dm3 pneumatic bioreactors: bubble column, split airlift, and concentric-tube airlift.
To develop correlations for γav based on superficial gas velocity and fluid rheological properties.
To compare the predicted γav values with those from classical correlations and assess their impact on Streptomyces clavuligerus cultivation.

Main Methods:

Applied a literature-based methodology to determine average shear rate (γav) using the volumetric oxygen transfer coefficient (k(L)a).
Developed empirical correlations for γav as a function of superficial gas velocity in the riser (U(GR)), consistency index (K), and flow index (n) for each bioreactor type.
Predicted γav during Streptomyces clavuligerus cultivations at a constant specific air flow rate (3.5 vvm) across the different bioreactors.

Main Results:

The proposed methodology yielded γav values consistent with classical correlations.
Bubble column bioreactors demonstrated the lowest γav, correlating with higher consistency index (K) values.
Concentric-tube airlift bioreactors exhibited the highest γav, associated with lower K values, impacting hyphal integrity.

Conclusions:

The study successfully established bioreactor-specific correlations for average shear rate (γav).
Bioreactor design significantly influences the shear environment, with implications for cell structure.
High shear rates, particularly in concentric-tube airlift bioreactors, can lead to hyphal rupture in Streptomyces clavuligerus.