10.26 Chemical Engineering Laboratory Fall, 1992
Sponsoring Companies: New Brunswick Scientific, Co.,
Inc., and Repligen Corporation
Genetic expression relates to the synthesis of specific proteins on the basis of genetic information. In our project, a recombinant gene coding for human platelet-factor 4 (PF-4) has been inserted -via a vector- into an Escherichia coli host strain. By definition, a gene is expressed when the synthesis of the protein of interest [here PF-4] can be determined. Human platelet factor-4 is a promising new drug with possible applications in AIDS research.
A continuous culture bioreactor refers to an open system for growing cells where the microbial population is maintained in a continuous state of balanced growth by continuously removing part of the culture and replacing it with fresh medium at the same rate.
In this project, we will operate the continuous culture as a chemostat which means that an essential growth-limiting nutrient will be fed to the system at a constant rate. By manipulating the rate of the feed, one can affect both the extent of growth and the growth rate of the culture while keeping the other process variables and the bioreactor volume unchanged. The process variables of interest include temperature, pH and dissolved oxygen. The chemostat technique offers a powerful tool to study the metabolism of an organism.
The production of PF-4 of the Repligen strain is under the control of a chemical inducer, IPTG (isopropyl-b-D-thiogalactopyranoside). Thus, after addition of IPTG to a growing culture, gene expression for PF-4 is triggered. The PF-4 protein is produced in the cell as an aggregate (called an inclusion body) visible by electron microscopy.