Abstract
Transformation is one mode of horizontal gene transfer (HGT) in bacteria, wherein extracellular naked DNA is taken up by cells that have developed genetic competence. Sensitivity to DNase, which degrades naked DNA, is the key to distinguishing transformation from the DNase-resistant HGT mechanisms. In general, Escherichia coli is not believed to be naturally transformable; it develops high competence only under artificial conditions, including exposure to high Ca2+ concentrations. However, E. coli can reportedly express modest competence under certain conditions that are feasible in natural environments outside laboratory. In addition, recent data suggest that environmental factors influence multiple routes of transformation. In this mini review, we (1) summarize our studies on transformation-based HGT using E. coli experimental systems and (2) discuss the possible occurrence of transformation via multiple mechanisms in the environment and its possible impact on the spread of antibiotic resistance genes.
Highlights
Horizontal gene transfer (HGT) between bacterial cells contributes to bacterial adaptation to various environments and, in the long term, to bacterial evolution (Lorenz and Wackernagel, 1994; Bushman, 2002; Thomas and Nielsen, 2005)
We summarize our studies on horizontal gene transfer (HGT) using E. coli experimental systems and discuss the possible occurrence of transformation by multiple mechanisms in natural environments and its possible impact on the spread of antibiotic resistance genes
We found that some E. coli collection of reference (ECOR) strains exhibited detectable transformability (10−10−10−11) in natural water at constant and varying temperatures between 5 and 35◦C and at winter temperatures in a field experiment, suggesting that natural E. coli can potentially develop competence under certain conditions that could feasibly occur in the environment (Matsumoto et al, 2016b)
Summary
Horizontal gene transfer (HGT) between bacterial cells contributes to bacterial adaptation to various environments and, in the long term, to bacterial evolution (Lorenz and Wackernagel, 1994; Bushman, 2002; Thomas and Nielsen, 2005). Previous studies on E. coli transformation exclusively focused on planktonic cells (Mandel and Higa, 1970; Hanahan, 1983), but we showed that E. coli cells within SA biofilms develop competence at a frequency of 10−6−10−8 on various solid media, including LB and H2O agar and various moist foods (Maeda et al, 2004).
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