Osmotic stability of the cell membrane of Escherichia coli from a temperature-limited fed-batch process

The temperature-limited fed-batch (TLFB) process is a technique where the oxygen consumption rate is controlled by a gradually declining temperature profile rather than a growth-limiting glucose-feeding profile. In Escherichia coli cultures, it has been proven to prevent an extensive release of endotoxins, i.e. lipopolysaccharides, that occurs in the glucose-limited fed-batch (GLFB) processes at specific growth rates below 0.1 h(-1). The TLFB and the GLFB process were compared to each other when applied to produce the periplasmic, constitutively expressed, enzyme beta-lactamase. The extraction of the enzyme was performed by osmotic shock. A higher production of beta-lactamase was achieved with the TLFB technique while no difference in the endotoxin release was found during the extraction procedure. Furthermore, it was found that growth at declining temperature, generated by the TLFB technique, gradually stabilizes the cytoplasmic membrane, resulting in a significantly increased product quality in the extract from the TLFB cultures in the osmotic shock treatment.