Product inhibition influence on immobilized cell biocatalyst performance

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Abstract
The potential steady-state influence of product inhibition on the performance of immobilized cell cultures is thoroughly explored with the aid of a simple unstructed reaction-diffusion model. Production inhibition was assumed to diminish the specific growth rate directly. The range of product sensitivity explored corresponds directly with the observed range of ethanol sensitivity of Clostridium thermocellum, Clostridium acetobutylicum, Saccharomyces uvarum, Zymomonas mobilis, and Saccharomyces cerevisiae. The consequent influence on the immobilized cell growth rate, thickness of steady-state viable cell layer, formation of growth-associated product, and global performance of the immobilized cell particle is explored by simulated variation of both the external bulk solution product level and the cell intrinsic sensitivity to the inhibitory product. Thus, both the thicknes of the steady-state viable cell layer and the consequent biomass loading of the bead are predicted variables of the model; these are variables due to the adaptive growth and biomass redistribution which occur in porous supports. The calculated influences are appreciable and even dramatic under some circumstances; the implications for packed-bed reactor operations for ethanol and solvent production are discussed.

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