Clostridium thermocellum is an anaerobic thermophilic bacterium that grows efficiently on cellulosic biomass. This bacterium produces and secretes a highly active multienzyme complex, the cellulosome, that mediates the cell attachment to and hydrolysis of the crystalline cellulosic substrate. C. thermocellum can efficiently utilize only ␤-1,3 and ␤-1,4 glucans and prefers long cellodextrins. Since the bacterium can also produce ethanol, it is considered an attractive candidate for a consolidated fermentation process in which cellulose hydrolysis and ethanol fermentation occur in a single process. In this study, we have identified and characterized five sugar ABC transporter systems in C. thermocellum.

Conventional observation of a fermentation process by using NAD(P)H-dependent fluorescence provides a mean for cell monitoring, but its practical application has been very limited due to many factors that affect culture fluorescence. In this work we studied correlation of scanning fluorometry signals with various process variables and with cell metabolic states and showed that scanning fluorometry is more informative than conventional NAD(P)H-dependent fluorescence. A stepwise multiple-regression procedure has been used to select meaningful signals from the whole spectrum, and we found that with three or four components of the excitation-emission plane the process variables can be portrayed with a rather good accuracy. The approach is demonstrated on the examples of wild-type or recombinant Escherichia coli and Saccharomyces cerevisiae fermentations.

The principles of bioanalytical systems for an on-line bioprocess monitoring are described within this paper. These sensor systems can be interfaced to the bioprocess in different ways according to the needs of the single bioprocess. Modular systems are necessary, which can fit exactly to the needs of the single process. Invasive as well as non-invasive bioanalytical tools are described and discussed in detail. Immunosensors give the possibility to monitor high molecular weight components within short time intervals. Non-invasive optical sensors allow the direct monitoring of various analytes such as oxygen pH for the complex fluorescence behavior of the bioprocess medium. These so-called fluorescence sensors offer the possibility to monitor intra-as well as extracellular components without interfering with the bioprocess. An industrial example for the application of bioanalytical tools for a process optimization are presented in this application. Here a biosensor system is used to optimize the downstreaming of molasses on a technical scale. The economic as well ecological advantages are discussed.

Stoichiometric relationships in the metabolic pathway of Clostridium acetobutylicum are used to formulate a framework for the analysis of pathway rates. This analytical tool, alone and in conjunction with intracellular NAD(P)H fluorescence measurements, is applied to two batch fermentations, one acidogenic and one solventogenic, to provide information on intracellular activities not readily obtainable by other methods.

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