Identification and Characterization of oriT and Two Mobilization Genes Required for Conjugative Transfer of Salmonella Genomic Island 1.

János Kiss,János Kiss,Gregory Douard,Benoît Doublet,Karine Praud,Mónika Szabó,István Nagy,István Nagy,Ferenc Olasz,Ferenc Olasz,Anna Hegyi,Anna Hegyi,Anna Hegyi,Axel Cloeckaert

doi:10.3389/fmicb.2019.00457

Abstract

The integrative mobilizable elements of SGI1-family considerably contribute to the spread of resistance to critically important antibiotics among enteric bacteria. Even though many aspects of SGI1 mobilization by IncA and IncC plasmids have been explored, the basic transfer elements such as oriT and self-encoded mobilization proteins remain undiscovered. Here we describe the mobilization region of SGI1 that is well conserved throughout the family and carries the oriTSGI1 and two genes, mpsA and mpsB (originally annotated as S020 and S019, respectively) that are essential for the conjugative transfer of SGI1. OriTSGI1, which is located in the vicinity of the two mobilization genes proved to be a 125-bp GC-rich sequence with several important inverted repeat motifs. The mobilization proteins MpsA and MpsB are expressed from a bicistronic mRNA, although MpsB can be produced from its own mRNA as well. The protein structure predictions imply that MpsA belongs to the lambda tyrosine recombinase family, while MpsB resembles the N-terminal core DNA binding domains of these enzymes. The results suggest that MpsA may act as an atypical relaxase, which needs MpsB for SGI1 transfer. Although the helper plasmid-encoded relaxase proved not to be essential for SGI1 transfer, it appeared to be important to achieve the high transfer rate of the island observed with the IncA/IncC-SGI1 system.

Highlights

Conjugation is a widespread mechanism of horizontal gene transfer among naturally occurring plasmids and genomic islands
These plasmids were introduced into the S. enterica serovar Agona strain 47SA97SGI1 int harboring the IncC helper plasmid R55 and their mobilization were assessed in mating assays
PACYC-10 could not be mobilized in the absence of Salmonella genomic island 1 (SGI1) int in the donor strain

Summary

Introduction

Conjugation is a widespread mechanism of horizontal gene transfer among naturally occurring plasmids and genomic islands. DNA is transferred from donor to recipient through a close cell-to-cell contact. Based on Gram-negative plasmid models, the process starts with the assembly of a multi-protein complex called the relaxosome around the origin of transfer (oriT). OriT is a cis-acting DNA region that is required for initiation of the transfer. The key enzyme of transfer initiation is the relaxase, which cuts either strand of oriT DNA at the nic site. The relaxase remains covalently bound to the 5 -end of the cleaved strand, which is subsequently delivered to

Methods

Results

Conclusion