Summary: A method for studying plasmid transfer in the rhizosphere is described. This work demonstrates plasmid transfer in an unenclosed rhizosphere under field conditions. The donor (Pseudomonas marginalis 376N) and recipient (Pseudomonas aureofaciens 381R) bacteria and the conjugative mercury resistance plasmid (pQBR11) studied were all isolated from the bacterial community indigenous to sugar beet rhizosphere. Spontaneous nalidixic acid and rifampicin resistant mutants of these bacteria were used as donors and recipients of pQBR11 for in situ matings. Fresh field soil was mixed with donors and recipients to give a soil mating mix (SMM) which was placed underground on the surface of a sugar beet root storage organ. Plasmid transfer in the SMM was determined after 24 h at frequencies between 5.1 × 10-5 and 1.3 × 10-8 transconjugants per recipient. Higher transfer frequencies (1.3 × 10-2 to 1.7 × 10-6) were recorded on the peel adjacent to the SMM. No transfer of mercury resistance was detected in SMM controls incubated at 20°C in vitro or placed in soil at distances of more than 5 cm from plants.
BashanY.1986; Migration of the rhizosphere bacteria Azospirillum brasilense and Pseudomonas fluorescens towards wheat roots in the soil. J Gen Microbiol 132:3407–3414
van ElsasJ. D.,
TrevorsJ. T.,
StarodubM.E.,
van OverbeekL. S.1990; Transfer of plasmid RP4 between Pseudomonads after introduction into soil — influence of spatial and temporal aspects of inoculation. FEMS Microbiol Ecol 73:1–11
FryJ.C.,
DayM.J.1990; Plasmid transfer in the epilithon. In Bacterial Genetics in Natural Environments pp. 55–80 Edited by
FryJ. C.,
DayM. J.
London: Chapman & Hall;
JacobsM. J.,
BugbeeW.M.,
GabrielsonD.A.1985; Enumeration, location, and characterisation of endophytic bacteria within sugar beet roots. Can J Bot 63:1262–1265
McClureN.C.,
WeightmanA.J.,
FryJ.C.1989; Survival of Pseudomonas putida UWC1 containing cloned catabolic genes in a model activated-sludge unit. Appl Environ Microbiol 55:2627–2634
RochelleP. A.,
BaleM. J.,
DayM.J.,
FryJ.C.1986; An accurate method for estimating sizes of small and large plasmids and DNA fragments by gel-electrophoresis. J Gen Microbiol 132:53–59
RochelleP. A.,
FryJ.C.,
DayM.J.1989; Factors affecting conjugal transfer of plasmids encoding mercury resistance from pure cultures and mixed natural suspensions of epilithic bacteria. J Gen Microbiol 135:409–424
StotzkyG.1989; Gene transfer among bacteria in soil. In Gene Transfer in the Environment pp 165–222 Edited by
LevyS. B.,
MillerR. V.
New York: McGraw-Hill;
TopE.,
MergeayM.,
SpringaelD.,
VerstraeteW.1990; Gene escape model — transfer of heavy-metal resistance genes from Escherichia coli to Alcaligenes eutrophus on agar plates and in soil samples. Appl Environ Microbiol 56:2471–2479
WellingtonE.M. H.,
CresswellN.,
HerronP. R.,
ClewlowL. J.,
SaundersV.A.,
WipatA.1990; Gene transfer between streptomycetes in soil. In Bacterial Genetics in Natural Environments pp. 216–230 Edited by
FryJ. C.,
DayM. J.
London: Chapman & Hall;
XuG.W.,
GrossD.C.1988; Physical and functional analyses of the Syr A and Syr B genes involved in syringomycin production by Pseudomonas syringae pv. syringae. J Bacteriol 170:5680–5688