Plasmids can switch between different transfer machineries depending on its genomic background

TORRES TEJERIZO, G. A.; PISTORIO, M.; DIP, D.; SALTO, I. P.; CERVANTES, L.; LAGARES, A.; ROMERO, D.; BROM, S.

Palm Cove

Congreso; International Plasmid Biology Conference; 2014

International Society for Plasmid Biology

Plasmids have played a major role in bacterial evolution, mainly by their capacity to perform horizontal gene transfer. Their conjugative transfer (CT) properties are usually described in terms of the plasmid itself. We analyzed structural and functional aspects of the conjugative transfer of pLPU83a, an accessory replicon from Rhizobium sp. LPU83, able to transfer from its parental strain, from Ensifer meliloti or from Rhizobium etli. pLPU83a contains a complete set of transfer genes, featuring a particular organization, shared with only two other rhizobial plasmids. These plasmids contain a TraR quorum-sensing (QS) transcriptional regulator, but lack an acyl-homoserine lactone synthase gene. We also determined that the ability of pLPU83a to transfer from R. etli CFN42 genomic background was mainly achieved through mobilization, employing the machinery of the endogenous plasmid pRetCFN42a, falling under control of the QS regulators from pRetCFN42a. In contrast, from its native or from the E. meliloti background, pLPU83a utilized its own machinery for conjugation, requiring the plasmid-encoded traR. Activation of TraR seemed to be acyl-homoserine lactone-independent and hypothetical genes placed between Dtr and Mpf genes could played a role in CT. Our results indicate that the CT phenotype (conjugative or mobilizable) could depend on the interaction among elements from different replicons, and not only on the plasmid itself; therefore, the wide-spread assumption that a plasmid has a defined CT behavior should be carefully evaluated from several related hosts. A plasmid may perform CT using regulatory elements carried on the plasmid, interacting with elements from other replicons, alternatively, in another genomic background; the same plasmid may achieve CT relying exclusively on the intrinsic machinery. Elucidation of the mechanisms that differentially regulate plasmid CT in different genomic backgrounds will be helpful to understand the boundaries of plasmid exchange in bacteria.