Shuttle transfer (or retrotransfer) of chromosomal markers mediated by plasmid pULB113

Abstract

The IncP1 plasmid pULB113 (RP4::miniMu) not only mediates the transfer of chromosomal markers in the classical direction (i.e. from the donor to the recipient cell) but also in the opposite direction (i.e. from the recipient bacterium to the donor). This phenomenon of retrotransfer was observed in homologous matings with Pseudomonas fluorescens, Alcaligenes eutrophus and Salmonella typhimurium. Retrotransconjugants could be discriminated from direct transconjugants by appropriate chromosomal and plasmid markers used to distinguish the mating partners not bearing pULB113. Retrotransfer of chromosomal markers occurred at frequencies equal to, or sometimes greater than, those observed for the direct mobilization, thus allowing the recovery of "recipient" recessive markers in the "donor" with linkage values similar to those found in the normal direction. Retrotransfer was also observed in heterospecific matings involving A. eutrophus and pULB113 bearing P. fluorescens: R-primes carrying different selected and unselected markers were recovered in both bacteria. "Retrotransfer" or "shuttle transfer" seems to be a specific trait of IncP1 plasmids.

Retrotransfer or gene capture: a feature of conjugative plasmids, with ecological and evolutionary significance

“…The terms ' retrotransfer ', ' shuttle transfer ', plasmid-mediated ' gene capture ' or even a kind of bacterial ' hermaphroditism ', were used to describe a conjugational biparental event that led to the inheritance (capture) by the original host of a conjugative plasmid, of genetic traits (either chromosomal markers or plasmids) from the mating partner, free of conjugative plasmids. The frequency of this retrotransfer can be very high, being in some cases of the same order of magnitude as the frequencies observed for the transfer of genetic traits promoted in the canonical donor-recipient direction (Mergeay et al, 1987). Although the phenomenon was first observed and analysed in most detail for broad-host-range (BHR) IncP1 plasmids (Mergeay et al, 1987), it was also reported for other plasmids such as some IncN (pULG14) and IncM plasmids (R69.2) (Thiry et al, 1984 ;Mergeay et al, 1985), the IncF plasmid pDE-FL54 and the IncW plasmid pSa322 (Heinemann & Ankenbauer, 1993a), and for the catabolic IncP9 plasmid pWW0 (RamosGonzalez et al, 1994).…”

“…The frequency of this retrotransfer can be very high, being in some cases of the same order of magnitude as the frequencies observed for the transfer of genetic traits promoted in the canonical donor-recipient direction (Mergeay et al, 1987). Although the phenomenon was first observed and analysed in most detail for broad-host-range (BHR) IncP1 plasmids (Mergeay et al, 1987), it was also reported for other plasmids such as some IncN (pULG14) and IncM plasmids (R69.2) (Thiry et al, 1984 ;Mergeay et al, 1985), the IncF plasmid pDE-FL54 and the IncW plasmid pSa322 (Heinemann & Ankenbauer, 1993a), and for the catabolic IncP9 plasmid pWW0 (RamosGonzalez et al, 1994). This capture of new genetic traits could thus be of great significance for the evolution of microbial communities, especially where stress is selecting rare events, yielding individual populations with new combinations of genes, which may allow better survival or more rapid growth.…”

“…In these scenarios, mobilization was always considered as a gene flow from the original donor to the recipient strain. However, the first report of gene flow at high frequencies in two directions was published by Mergeay et al in 1987. By means of an IncP conjugative plasmid, chromosomal genes were not only mobilized from the original donor of the IncP plasmid towards the plasmid-free recipient, but also from the original recipient back into the donor.…”

“…The capture of chromosomal markers was first observed during conjugation mediated by derivatives of IncP plasmids carrying a transposable element (Mergeay et al, , 1987 such as R68.45 and RP4 : : Mu3A (also called pULB113 ; Van Gijsegem & Toussaint, 1982). The matings involved a donor with multiple markers spread over the chromosome and a recipient carrying one marker.…”

“…1. Schematic of an RP4 : : Mu3A-mediated cross designed to distinguish retrotransconjugants from direct transconjugants [inspired from data published in Mergeay et al (1987)]. The reported cross involves an A + B − C − D − E − F − donor carrying the conjugative plasmid RP4 : : Mu3A and a recipient A − B + C + D + E + F + strain carrying the Tra − Mob − plasmid pKT261, used here exclusively to mark the recipients.…”