High cell density cultures of escherichia coli B and rhodotorula glutinis

Abstract

High cell density cultures of two model microorganisms were carried out in fed-batch system using pure oxygen. Major constraints in this type of culture were studied with Escherichia coli(facultative anaerobe) and Rhodotorula glutinis (obligate aerobe) as the model microbes. In the high density culture of E. coli B, final concentration of the biomass was increased to 85-95 g/L. During the culture, gradual decreases of the biomass yield and the specific growth rate were observed, which seemed to be due to the build-up of by-products and high partial pressure of CO2. Accumulation of the byproducts was not due to the limitation of oxygen, but due to the kinetic adaptation of E. coli. By-products exerted their negative effects on the specific growth rate and the biomass yield. Extent of by-products accumulation was affected significantly by operating conditions of the culture. It was possible to bypass accumulation of the by-products by restricting the ``relative`` growth rate of E. coli. With increase of pCO2, the maximum specific growth rate was decreased. Continuous culture as a method of screening the inhibitory or stimulatory substances was critically discussed with the result of high pCO2 inhibition. It is, therefore, reasonable to say that in the high cell density culture of facultative anaerobe (E.coli) the major constraints are the accumulation of by-products and the high partial pressure of CO2. In the high cell density culture of R. glutinis, no physiological constraints were observed; i.e. R. glutinis may be grown up to the point where volume of the bioreactor is physically occupied by the cells themselves. Final concentration of the biomass obtained was 185 g/L, and volume of cells at this concentration corresponded to about 70\% of bioreactor volume. Lipid content was 40\% of the dry biomass. R. glutinis could be also grown up to 110 g/L with air only because this microorganism grew without accumulation of by-products under the oxygen or nitrogen limi...