Evolutionary relationships, genomic organization and characterization of novel genes that increase and decrease conjugative plasmid transfer

CASTELLANI L.G.; PISTORIO M.; BROM S.; NILSSON J.F.; TORRES TEJERIZO G.A.

Cambridge

Congreso; International Conference on Plasmids and other Mobile Genetic Elements; 2016

Plasmids are widely found in rhizobia, a group of bacteria that are able to perform symbiotic relationship with the roots of legumes. The size of these plasmids ranges from a few Kbp to 2 Mbp. Several works have described the conjugative transfer of these elements; Ding & Hynes [1] grouped rhizobial plasmids by their Mpf and Dtr systems. Recently, we showed that hypothetical genes located between the Mpf and Dtr in pRetCFN42a are also involved in CT of this plasmid [2]. Conjugative transfer (CT) in pRetCFN42a is regulated by the acyl-homoserine lactone (HSL)-dependent TraR regulator. Plasmid pLPU83a, an accessory replicon from Rhizobium sp. LPU83, is able to transfer, but the mechanisms that regulate its CT are not fully understood, since it needs TraR but not HSL [3]. These features make pLPU83a an interesting plasmid for studying novel mechanism of CT regulation.Here, we studied the functionality, genomic organization and evolutionary relationships of hypothetical genes located between Mpf and Dtr in pLPU83a. Three in-tandem genes were found. Mutant derivatives of these genes revealed that inactivation of the first one abolished CT (pLPU83_148), while mutation of the downstream gene enhanced CT (pLPU83_146). The third gene (pLPU83_145) did not show a clear phenotype. By RNAseq analysis these genes do not seem to form an operon, suggesting a new scheme of regulation of plasmid transfer. Moreover, the search for homologous genes in databases showed that pLPU83_148 homologs were found almost exclusively in Alphaproteobacteria (98%), while homologs of pLPU83_145 and pLPU83_146 were more dispersed, with 25% and 65% of the hits in Alphaproteobacteria, respectively. Insights into CT regulation established by these genes, and into their prevalence in other plasmids will help to the comprehension of the modulation mechanisms of CT of plasmids.1.Ding, H. and M.F. Hynes (2009) Can J Microbiol. 55, 917-27.2.Lopez-Fuentes, E. (2015) Front Microbiol, 5, 793.3.Torres Tejerizo, G. (2014) FEMS Microbiol Ecol 88, 565?578.