TY - JOUR

T1 - Root growth and exudate production define the frequency of horizontal plasmid transfer in the Rhizosphere

AU - Mølbak, Lars

AU - Molin, Søren

AU - Kroer, Niels

PY - 2007/1/1

Y1 - 2007/1/1

N2 - To identify the main drivers of plasmid transfer in the rhizosphere, conjugal transfer was studied in the rhizospheres of pea and barley. The donor Pseudomonas putida KT2442, containing plasmid pKJK5::gfp, was coated onto the seeds, while the recipient P. putida LM24, having a chromosomal insertion of dsRed, was inoculated into the growth medium. Mean transconjugant-to-donor ratios in vermiculite were 4.0±0.8 × 10-2 in the pea and 5.9±1.4 × 10-3 in the barley rhizospheres. In soil, transfer ratios were about 10 times lower. As a result of a 2-times higher root exudation rate in pea, donor densities in pea (1 × 106-2 × 109 CFU g-1 root) were about 10 times higher than in barley. No difference in recipient densities was observed. In situ visualization of single cells on the rhizoplane and macroscopic visualization of the colonization pattern showed that donors and transconjugants were ubiquitously distributed in the pea rhizosphere, while they were only located on the upper parts of the barley roots. Because the barley root elongated about 10 times faster than the pea root, donors were probably outgrown by the elongating barley root. Thus by affecting the cell density and distribution, exudation and root growth appear to be key parameters controlling plasmid transfer in the rhizosphere.

AB - To identify the main drivers of plasmid transfer in the rhizosphere, conjugal transfer was studied in the rhizospheres of pea and barley. The donor Pseudomonas putida KT2442, containing plasmid pKJK5::gfp, was coated onto the seeds, while the recipient P. putida LM24, having a chromosomal insertion of dsRed, was inoculated into the growth medium. Mean transconjugant-to-donor ratios in vermiculite were 4.0±0.8 × 10-2 in the pea and 5.9±1.4 × 10-3 in the barley rhizospheres. In soil, transfer ratios were about 10 times lower. As a result of a 2-times higher root exudation rate in pea, donor densities in pea (1 × 106-2 × 109 CFU g-1 root) were about 10 times higher than in barley. No difference in recipient densities was observed. In situ visualization of single cells on the rhizoplane and macroscopic visualization of the colonization pattern showed that donors and transconjugants were ubiquitously distributed in the pea rhizosphere, while they were only located on the upper parts of the barley roots. Because the barley root elongated about 10 times faster than the pea root, donors were probably outgrown by the elongating barley root. Thus by affecting the cell density and distribution, exudation and root growth appear to be key parameters controlling plasmid transfer in the rhizosphere.

KW - Exudates

KW - Horizontal transfer

KW - pKJK5

KW - Plasmid

KW - Rhizosphere

UR - http://www.scopus.com/inward/record.url?scp=33845682608&partnerID=8YFLogxK

U2 - 10.1111/j.1574-6941.2006.00229.x

DO - 10.1111/j.1574-6941.2006.00229.x

M3 - Journal article

C2 - 17069619

AN - SCOPUS:33845682608

VL - 59

SP - 167

EP - 176

JO - F E M S Microbiology Ecology

JF - F E M S Microbiology Ecology

SN - 0168-6496

IS - 1

ER -