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Appl Environ Microbiol, March 1998, p. 880-889, Vol. 64, No. 3
Institute for Plant Protection IPO-DLO,
Received 28 April 1997/Accepted 22 September 1997
A set of self-transmissible plasmids with IncQ plasmid-mobilizing
capacity was isolated by triparental exogenous isolation from the wheat
rhizosphere with an Escherichia coli IncQ plasmid host and
a Ralstonia eutropha recipient. Three plasmids of 38 to 45 kb, denoted pIPO1, pIPO2, and pIPO3, were selected for further study.
No selectable traits (antibiotic or heavy-metal resistance) were
identified in these plasmids. The plasmids were characterized by
replicon typing via PCR and hybridization with replicon-specific probes
and other hybridizations. pIPO1 and pIPO3 were similar to each other,
whereas pIPO2 was different. None of these plasmids belonged to any
known incompatibility group. pIPO2 was selected for further work, and a
mini-Tn5-tet transposon was inserted to confer
selectability. Plasmid pIPO2 had a broad IncQ plasmid mobilization and
self-transfer range among the alpha, beta, and gamma subclasses of the
Proteobacteria but did not show productive transfer to gram-positive bacteria. Plasmid pIPO2 mobilized IncQ plasmid pIE723 from Pseudomonas fluorescens to diverse indigenous
proteobacteria in the rhizosphere of field-grown wheat. Transfer of
pIE723 to indigenous bacteria was not observed in the absence of added
pIPO2. A specific PCR primer system and a probe were developed for the detection of pIPO2-type plasmids in soil and rhizosphere. Analysis of
soil DNA provided evidence for the presence of pIPO2 in inoculated wheat rhizosphere soil in the field study, as well as in the
rhizosphere of uninoculated wheat plants growing in soil microcosms.
The system failed to identify major reservoirs of pIPO2 in a variety of
other soils.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Isolation, Characterization, and Transfer of Cryptic
Gene-Mobilizing Plasmids in the Wheat Rhizosphere
*
Corresponding author. Mailing address: IPO-DLO, P.O.
Box 9060, 6700GW Wageningen, The Netherlands. Phone: 31.317.476210. Fax: 31.317.410113. E-mail: J.D.VANELSAS{at}IPO.DLO.NL.
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