Cellular Responses to Strong Overexpression of Recombinant Genes in Escherichia Coli

Changes in the physiology of Escherichia coli cells producing a recombinant α-glucosidase were studied in glucose limited fed-batch fermentations. High α-glucosidase formation is connected to growth inhibition and loss of culturability. Although some metabolic functions are maintained, the ability for replication is apparently not only impaired by competition of recombinant product synthesis to the formation of cellular house-keeping proteins, but is related to continued damage of the chromosomal DNA, which is concluded from electron microscopical analysis and from the behaviour of the SOS response repressor protein LexA. Although, from the decrease of LexA, we propose an SOS signal, the cells are unable to induce the SOS response, due to the high synthesis of α-glucosidase and the concurrent inhibition of the protein synthesis system.