The EcoKI type I restriction-modification system in Escherichia coli affects but is not an absolute barrier for conjugation.

The rapid evolution of bacteria is crucial to their survival and is caused by exchange, transfer, and uptake of DNA, among other things. Conjugation is one of the main mechanisms by which bacteria share their DNA, and it is thought to be controlled by varied bacterial immune systems. Contradictory results about restriction-modification systems based on phenotypic studies have been presented as reasons for a barrier to conjugation with and other means of uptake of exogenous DNA. In this study, we show that inactivation of the R.EcoKI restriction enzyme in strain Escherichia coli K-12 strain MG1655 increases the conjugational transfer of plasmid pOLA52, which carriers two EcoKI recognition sites. Interestingly, the results were not absolute, and uptake of unmethylated pOLA52 was still observed in the wild-type strain (with an intact hsdR gene) but at a reduction of 85% compared to the uptake of the mutant recipient with a disrupted hsdR gene. This leads to the conclusion that EcoKI restriction-modification affects the uptake of DNA by conjugation but is not a major barrier to plasmid transfer.