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Appl. Environ. Microbiol., Oct 1996, 3673-3678, Vol 62, No. 10
B Baur, K Hanselmann, W Schlimme and B Jenni
Until now, Escherichia coli was thought to be unable to develop natural
competence, i.e., genetic transformation could be achieved only
artificially with the aid of nonphysiological concentrations of calcium
ions or by other treatments. We have tested the competence development of
E. coli through transformation under natural conditions in river water,
springwater, and mineral water which contained between 0 and 11 mM Ca2+,
using pUC18 DNA. The presence of calcium ions at concentrations as low as 1
to 2 mM was sufficient to obtain transformants. Variations in the
temperature of incubation were not required for competence development but
had an influence on the transformation frequency. Using water from mineral
springs originating from calcareous regions, we have obtained
transformation frequencies with laboratory strains of E. coli similar to
those reported for other gram-negative bacteria known to develop natural
competence. The competence development of E. coli is most probably
internally regulated (as for the other gram-negative bacteria), and
inadequate conditions chosen for the transformation tests in the laboratory
might impair the detection of higher natural transformation frequencies.
The results will enhance our knowledge about the fate of laboratory or
production strains of E. coli cells reaching natural aquatic ecosystems.
Copyright © 1996, American Society for Microbiology
Genetic transformation in freshwater: Escherichia coli is able to develop natural competence
Department of Microbiology, University of Zurich, Switzerland.
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