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Appl. Environ. Microbiol., Apr 1997, 1577-1583, Vol 63, No. 4
AK Lilley and MJ Bailey
The transfer of naturally occurring conjugative plasmids from the
indigenous microflora to a genetically modified population of bacteria
colonizing the phytospheres of plants has been observed. The marked strain
(Pseudomonas fluorescens SBW25EeZY6KX) was introduced as a seed dressing to
sugar beets (Beta vulgaris var. Amethyst) as part of a field experiment to
assess the ecology and genetic stability of deliberately released bacterial
inocula. The sustained populations of the introduced strain, which
colonized the phytosphere, were assessed throughout the growing season for
the acquisition of plasmids conferring mercury resistance (Hg(supr)).
Transconjugants were isolated only from root and leaf samples collected
within a narrow temporal window coincident with the midseason maturation of
the crop. Conjugal-transfer events were recorded during this defined period
in two separate field release experiments conducted over consecutive years.
On one occasion seven of nine individual plants sampled supported
transconjugant P. fluorescens SBW25EeZY6KX, demonstrating that conjugative
gene transfer between bacterial populations in the phytosphere may be a
common event under specific environmental conditions. The plasmids acquired
in situ by the colonizing inocula were identified as natural variants of
restriction digest pattern group I, III, or IV plasmids from five
genetically distinct groups of large, conjugative mercury resistance
plasmids known to persist in the phytospheres of sugar beets at the field
site. These data demonstrate not only that gene transfer may be a common
event but also that the genetic and phenotypic stability of inocula
released into the natural environment cannot be predicted.
Copyright © 1997, American Society for Microbiology
The Acquisition of Indigenous Plasmids by a Genetically Marked Pseudomonad Population Colonizing the Sugar Beet Phytosphere Is Related to Local Environmental Conditions
Molecular Microbial Ecology Laboratory, Institute of Virology and Environmental Microbiology, Natural Environment Research Council, Oxford, OX1 3SR, United Kingdom
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