Fusion proteins, engineered proteins that combine the DNA sequences and therefore properties of two different proteins, can be used in a variety of therapeutic purposes. One example of a therapeutic fusion protein is collagen binding domain-parathyroid hormone glutathione-S-transferase (CBD-PTH-GST), which can combat osteoporosis by binding specifically to collagen in the vertebral column and promoting bone growth through the release of calcium. This fusion protein is being expressed with Escherichia coli at the University of Arkansas through fed-batch fermentation, a method that produces large volume of cells through fermentation in a controlled environment in a bioreactor. It is necessary to track cell growth during fed-batch fermentation, and typical methods include measuring optical density (OD) with a spectrophotometer. However, this machine is limited in the range of OD it can measure without dilution and requires removal of samples from the bioreactor. Alternatively a noninvasive OD probe can be used to monitor cell growth during fed-batch fermentation, such as the BE2100 Noninvasive Biomass Sensor, or BugEye probe. Unfortunately the relationship between BugEye units and spectrophotometer OD is not well understood. This study was conducted in order to investigate the relationship between the BugEye probe and spectrophotometer OD and whether or not this relationship was affected by the RPM of the stirrer in the bioreactor during fermentation
