Surface Modifications for Controlled and Optimized Cell Immobilization by Adsorption: Applications in Fibrous Bed Bioreactors Containing Recombinant Cells

Peter Kilonzo

doi:10.4172/1948-5948.s8-001

Abstract

The effects of surface properties of S. cerevisiae strains 468/pGAC9 and 468 on adhesion to polyethylenimine (PEI) and/glutaraldehyde (GA) pretreated cotton (CT), polyester (PE), polyester + cotton (PECT), nylon (NL), polyurethane foam (PUF), and cellulose re-enforced polyurethane (CPU) fibers were investigated. Process parameters (circulation velocity, pH, ionic strength, media composition and surfactants) were also examined. 80, 90, and 35% of the cells were adsorbed onto unmodified CT, PUF and PE, respectively. PEI-GA pre-treated CT and alkali treated PE yielded 25% and 60% cell adhesion, respectively. Adsorption rate (Ka) ranged from 0.06 to 0.17 for CT and 0.06 to 0.16 for PE at varied pH. Adhesion increased by 15% in the presence of ethanol, low pH and ionic strength, and decreased by 23% in the presence of yeast extract and glucose. Shear flow and 1% Triton X-100 detached 62 and 36% nonviable cells from PE and CT, respectively, suggesting that cell immobilization in fibrousbed bioreactors can be controlled to optimize cell density for long-term stability.

Highlights

The immobilization of viable cells has been defined by several investigators as the physical confinement or localization of viable microbial cells to a certain defined region of space in such a way as to limit their free migration and exhibit hydrodynamic characteristic which differ from those of the surrounding environment while retaining their catalytic activities for repeated and continuous use [1].Cell immobilization is often used to improve the performance of traditional continuous fermentation process by increasing the amount of cells per bioreactor volume, and cell deposition on supports or inclusion in gel matrices has been applied to promote plasmid stability of recombinant cells [1-3]
Different from the inherent problems associated with cell entrapment [7], cell immobilization through adsorption provides a direct contact between nutrients and the immobilized cells, eliminating such concerns
S. cerevisiae strain 468/pGAC9 (ATCC 20690) was stored on selective YNBG agar slants containing 6.7 g L-1 yeast nitrogen base (YNB) without amino acids (Sigma), 0.04 g L-1 L-histidine (Sigma), and 20 g L-1 D-glucose and cultivated in YNBM supplemented with 2% (w v-1) maltose and Fermtech-agar [2]

Summary

Introduction

The immobilization of viable cells has been defined by several investigators as the physical confinement or localization of viable microbial cells to a certain defined region of space in such a way as to limit their free migration and exhibit hydrodynamic characteristic which differ from those of the surrounding environment while retaining their catalytic activities for repeated and continuous use [1].Cell immobilization is often used to improve the performance of traditional continuous fermentation process by increasing the amount of cells per bioreactor volume, and cell deposition on supports or inclusion in gel matrices has been applied to promote plasmid stability of recombinant cells [1-3]. Lebrun et al [4], attempted immobilizing cells in microporous beads or gels by entrapment In both systems the anticipated benefits such as increased cell density, stability, productivity, permeability, and enhanced resistance to environmental perturbations, and expedited cofactor regeneration [5,6], were not realized due to accumulation of dead cells and poor mass transfer under high cell density conditions. Different from the inherent problems associated with cell entrapment [7], cell immobilization through adsorption provides a direct contact between nutrients and the immobilized cells, eliminating such concerns This cell immobilization technique involves the transport of the cells from the bulk phase to the surface of support, followed by the adhesion of cells, and subsequent colonization of the support surface. Both electrostatic and hydrophobic interactions govern the cell-support adhesion, which is the key step in controlling the cell immobilization on the support

Methods

Results

Conclusion