Online monitoring of biomass accumulation in recombinant yeast cultures

Expression and Purification of Membrane Proteins in Saccharomyces cerevisiae

Saccharomyces cerevisiae is one of the most popular expression systems for eukaryotic membrane proteins. Here, we describe protocols for the expression and purification of mitochondrial membrane proteins developed in our laboratory during the last 15 years. To optimize their expression in a functional form, different promoter systems as well as codon-optimization and complementation strategies were established. Purification approaches were developed which remove the membrane protein from the affinity column by specific proteolytic cleavage rather than by elution. This strategy has several important advantages, most notably improving the purity of the sample, as contaminants stay bound to the column, thus eliminating the need for a secondary purification step, such as size exclusion chromatography. This strategy also avoids dilution of the sample, which would occur as a consequence of elution, precluding the need for concentration steps, and thus preventing detergent concentration.

Sensors for disposable bioreactors

Modern bioprocess monitoring demands sensors that provide on-line information about the process state. In particular, sensors for monitoring bioprocesses carried out in single-use bioreactors are needed because disposable systems are becoming increasingly important for biotechnological applications. Requirements for the sensors used in these single-use bioreactors are different than those used in classical reusable bioreactors. For example, long lifetime or resistance to steam and cleaning procedures are less crucial factors, while a requirement of sensors for disposable bioreactors is a cost that is reasonable on a per-use basis. Here, we present an overview of current and emerging sensors for single-use bioreactors, organized by the type of interface of the sensor systems to the bioreactor. A major focus is on non-invasive, in-situ sensors that are based on electromagnetic, semiconducting, optical, or ultrasonic measurements. In addition, new technologies like radio-frequency identification sensors or free-floating sensor spheres are presented. Notably, at this time there is no standard interface between single-use bioreactors and the sensors discussed here. In the future, manufacturers should address this shortcoming to promote single-use bioprocess monitoring and control.