Online respiration activity measurement (OTR, CTR, RQ) in shake flasks

Online measurement of respiration activity (including oxygen transfer rate (OTR), carbon dioxide transfer rate (CTR), respiratory quotient (RQ)) of microbial cultures in stirred bioreactors with exhaust gas analysis has been state of the art for years. As much more experiments are conducted in shaking bioreactors compared to stirred bioreactors, Anderlei and Buchs [Biochem. Eng. J. 7 (2001) 157] developed a measuring device (OTR-Device) for online determination of the oxygen transfer rate in shake flasks under sterile conditions. In this paper, an extension of the OTR-Device, termed respiration activity monitoring system (RAMOS) is described, which allows additional measurement of the carbon dioxide transfer rate and the respiratory quotient in shaking bioreactors. Fermentations of the yeasts Saccharomyces cerevisiae and Pichia stipitis carried out with RAMOS are presented. These measurements show very clearly the differences in respiration activities between the Crabtree-positive yeast S. cerevisiae and the Crabtree-negative yeast P stipitis. Furthermore, a fermentation of the bacterium Corynebacterium glutamicum is presented, showing the influence of an oxygen limitation on the metabolic activities of the culture. Also, a fermentation of a hybridoma cell line was carried out with RAMOS to elucidate the measuring sensitivity of the system. The new device provides the most important and characteristic parameters (OTR, CTR, RQ) representing biological cultures online, enabling users to draw conclusions on metabolisms of microorganisms already in shaking bioreactors. (C) 2003 Elsevier B.V. All rights reserved.