Plasmid maintenance and physiology of a genetically engineered Escherichia coli strain during continuous l-carnitine production
The effect of immobilization on cell physiology and how this determines cell metabolic performance is an important concern for developing bioprocess. This is particularly true for genetically modified microorganisms and their genetic stability. For this reason the stability and physiological state of plasmid-bearing E. coli cells were ascertained by flow cytometry. Differences in the cellular DNA and protein content (15–20%) permit discrimination of control and plasmid-bearing cells, as well as adaptation to continuous cultivation conditions in both freely suspended and immobilized states to be monitored. Moreover, the observed metabolic burden due to maintenance and over-expression of plasmid-coded genetic material and slow cell growth in poorly-viable immobilized cells were found to be the main factors contributing to strain stabilization.
KeywordsEscherichia coli Flow cytometry Genetic stability l-Carnitine Metabolic burden
This work has been funded by MEC project BIO2005-08988-CO-1, CARM project 06 BIO2005/01-6468 and Fundación Séneca CARM project 2005 2928/PI/05. V. Bernal acknowledges research fellowships from Fundación Séneca-CARM and Fundación CajaMurcia.
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