Effects of Cell Recycle on Microbial Cell Viability and Metabolism

James D. Bryers

Abstract

Theoretically recycle of active cellular mass back to a continuous fermentation system can significantly improve system productivity. Only recently has membrane separation technology advanced to the state of providing sterile cell separation at 100% efficiency. This work studies the effect of increasing cell recycle ratios on microbial physiology and viability for two microorganisms, a bacterium Klebsiella pneumoniae and a yeast Saccharomyces cerevisae. Comparison of mathematical models, which account for endogenous decay, with experimental results indicate a mechanically induced lysis of bacterial cells that increased with increasing recycle ratio and decreasing dilution rate. In yeast studies, no similar cell damage was observed, but increasing cell recycle ratios did effect metabolism of yeast and altered internal pools of DNA, RNA, and total protein as determined by flow cytometry. Results indicate that steady state unstructured models can only satisfactorily simulate gross changes in cellular concentration in recycle systems but structured models are required to predict recycle effects on intracellular components and physiology.

Received November 12, 1987.
Accepted February 23, 1988.

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