Ability of Escherichia coli to Distinguish Between Self and Foreign DNA as Demonstrated by Trends in Transformation Efficiency

Abstract

Bacterial transformation is a widely used technique, yet its underlying mechanisms are not fully understood. This study investigated the effect of contaminating DNA on the transformation efficiency in two different strains of Escherichia coli (HB101 and B23) and attempted to determine whether E. coli is able to distinguish during transformation between its own (self) DNA and DNA originating from another strain or organism (foreign). First, p328.5 was isolated from Escherichia coli HB101 then transformed into E. coli B23 via CaCl 2 treatment or electroporation. Isolation of p328.5 from HB101 was relatively easy. Subsequent transformation into B23 failed with CaCl treatment but was successful by 2 electroporation. Secondly, we contaminated plasmid p328.5 DNA, isolated from the transformed B23 and HB101 cells, with genomic DNA originating from one of E. coli HB101, E. coli B23, or Bacillus subtilis WB746 and observed the effect on transformation efficiency in HB101 and B23. It was found in both strains that the presence of genomic DNA significantly affects transformation efficiency, in some cases reducing it by 50% and in other cases down to undetectable levels. It could not be concluded exactly what effect different origins of genomic DNA has on transformation, but there are indications that genomic B23 DNA has an increased ability to interfere with transformation in both HB101 and B23 strains of E. coli.