Fate of a genetically engineered escherichia coli bearing a plasmid in a paddy field microcosm

Abstract

Escherichia coli DH5 a pBluescript II SK⁺, bearing a plasmid which has a resistant gene to ampicillin as a genetically engineered bacteria (g‐E. coli) and its parent E. coli DH5 a (p‐E. coli), were introduced into a paddy field microcosm on the initial, 0.5th, 5th and 20th days after the microcosm was cultured. The population densities of both g‐E. coli and p‐E. coli decreased exponentially, irrespective of the day they were introduced. After that, p‐E. coli remained at 10² cells/ml level, but the population density of g‐E. coli was less than that of p‐E. coli and died out within 30 days. Neither g‐E. coli nor p‐E. coli had any effect on the population densities of indigenous bacteria and protozoa. From the point of population density, no interaction between g‐E. coli and p‐E. coli was found in the microcosm. Considering that there was no difference in the growth pattern between g‐E. coli and p‐E. coli in the single cultures in the microcosm medium, the indigenous community had the plasmid burden on the survival of g‐E. coli. It was suggested the g‐E. coli could be used safely in the paddy field judging from the final extinction of g‐E. coli in the paddy field microcosm.

Keywords:

• Escherichia coli
• plasmid
• paddy field microcosm
• population changes