Improved electro-transformation of highly DNA-restrictive corynebacteria with DNA extracted from starved Escherichia coli

Differences of up to 33 000-fold in electro-transformability of highly DNA restrictive corynebacteria are observed in the DNA of a shuttle plasmid extracted from Escherichia coli hosts propagated in different nutritional conditions. Growth of the host in minimal medium increases plasmid transformability, whereas growth on rich media decreases it. In the E. coli DH5 alpha. host, the starvation-dependent increase in DNA transformability is reverted by supplementing with methionine, an obligate S-adenosyl-methionine (SAM) precursor. This suggests that an E. coli nutritionally modulated SAM-dependent DNA-methyltransferase may be involved in this phenomenon.