Effect of Environmental Factors on the Expression of the Catabolite-Dependent lux-Operon Borne by a Recombinant Plasmid

Expression of the lux-genes cloned in the recombinant plasmid pPHL7 (Ap r Lux + ) in Escherichia coli Z905 cells was studied in various environments, including model aquatic ecosystems. Expression of the lux-genes strongly depended on the nutritional status of the medium. In particular, the cultivation of cells in nutrient-rich medium favored the maintenance of the initial level of expression of the lux-operon, whereas nutrient limitation induced recombinant cell variants with an impaired control of the catabolite-dependent luxoperon. On the other hand, long-term laboratory cultivation of the recombinant strain in nutrient-deficient media or its long-term life in model aquatic ecosystems led to the accumulation of cells with a stringent control on the cloned lux-genes in the bacterial population. The presence of the selective factor (ampicillin) in the medium had no significant effect on the expression of the lux-operon.