Horizontal Transfer of the High-Pathogenicity Island ofYersinia pseudotuberculosis

Abstract

The horizontal transfer of genetic elements plays a major role in bacterial evolution. The high-pathogenicity island (HPI), which codes for an iron uptake system, is present and highly conserved in various Enterobacteriaceae, suggesting its recent acquisition by lateral gene transfer. The aim of this work was to determine whether the HPI has kept its ability to be transmitted horizontally. We demonstrate here that the HPI is indeed transferable from a donor to a recipient Yersinia pseudotuberculosis strain. This transfer was observable only when the donor and recipient bacteria were cocultured at low temperatures in a liquid medium. When optimized conditions were used (bacteria actively growing in an iron-deprived medium at 4°C), the frequency of HPI transfer reached ϳ10 ؊8 . The island was transferable to various serotype I strains of Y. pseudotuberculosis and to Yersinia pestis, but not to Y. pseudotuberculosis strains of serotypes II and IV or to Yersinia enterocolitica. Upon transfer, the HPI was inserted almost systematically into the asn3 tRNA locus. Acquisition of the HPI resulted in the loss of the resident island, suggesting an incompatibility between two copies of the HPI within the same strain. Transfer of the island did not require a functional HPI-borne insertion-excision machinery and was RecA dependent in the recipient but not the donor strain, suggesting that integration of the island into the recipient chromosome occurs via a mechanism of homologous recombination. This lateral transfer also involved the HPI-adjacent sequences, leading to the mobilization of a chromosomal region at least 46 kb in size.Genomic islands are large pieces of chromosomal DNA which display characteristics of horizontally acquired elements (17). These elements frequently harbor phage-and/or plasmidderived sequences, but little is known about their mechanisms of lateral transfer. To date, only two genomic islands have been shown to be transmissible. The 105-kb clc ecological island of Pseudomonas spp. is transferable at low frequencies (Ϸ10 Ϫ8 ) to various ␥-and ␤-Proteobacteria (34, 41). The genetic bases for this transfer have not yet been elucidated. The 500-kb symbiosis island of Mesorhizobium loti is transferable at a frequency of 10 Ϫ7 to three Mesorhizobium species (42). The transmissibility of this island has been associated with the presence of the trb operon and the traG gene, which display homology to genes required for the conjugative transfer of some plasmids (43).The hypothesis that genomic islands could be transmitted by phages has been put forward because, as with bacteriophages, these islands are most often inserted into tRNA genes, they excise from the host chromosome by site-specific recombination between flanking direct repeats homologous to phage attachment sites, and their excision is mediated by a phagelike integrase and sometimes a recombination directionality factor (22,25,36). Pathogenicity islands (PAIs) are a subset of genomic islands characterized by their capacity to encode virulence function...

Oral Vaccination against Bubonic Plague Using a Live AvirulentYersinia pseudotuberculosisStrain

“…DNA was obtained by thermolysis of bacteria in a solution containing 50 mM NaOH and 0.25% sodium dodecyl sulfate. The primers (obtained from Proligo France) amplified the int gene of the high pathogenicity island (HPI) (24), the yopM (33), and yopK (forward, 5Ј-CTGCTCATTTACTGAGAACG-3Ј; reverse, 5Ј-CTATAAGTAGAGAGTTTTTCGG-3Ј), genes of the pYV virulence plasmid, the pilR and pilN genes of the type IV pilus locus (10), and the ypmAC or ypmB genes coding for YPM superantigens (15). The housekeeping gene ureB encoding an urease subunit was used as an internal positive control for the PCRs.…”

Horizontal transfer and functional evaluation of high pathogenicity islands in Avian Escherichia coli

“…The complex process of horizontal transfer may offer an explanation for this process, which can abolish the expression of HPI genes. Lesic and Carniel (2005) also found that the growth of the HPI recipient strain was inhibited under normal conditions, and virulence was also significantly reduced. Probably due to the process of HPI transfer, homologous recombination in recipient strains leads to the deletion and destruction of growth and virulence genes.…”

“…The results of Asn-tRNA loci PCR amplification showed that restructuring also occurred outside the HPI. Lesic and Carniel (2005) also found that HPI had high transfer frequencies at low temperatures and in conditions of low iron abundance, which showed that bacteria were under selective pressure to acquire the complete HPI. After the HPI is obtained by host bacteria, survival in different environments may require adaptive change, in which the function of the HPI is deactivated.…”

“…It suggests that Asn-tRNA plays a role in targeting gene transfer via bacteriophages and plasmids (Hacker and Kaper 2000), and thus that Asn-tRNA is a key element required for bacterial evolution. Lesic and Carniel (2005) HPI transfer was dependent on homologous recombination in the recipient strain, and that adjacent contiguous sequences were also moved. The results of Asn-tRNA loci PCR amplification showed that restructuring also occurred outside the HPI.…”

“…Two HPI + isolates without chloramphenicol resistance were chosen as donor strains, and were named AE-d1 and AE-d2. The acceptor strains and donor strains were inoculated together and co-cultured in LB containing 1% 2,2'-bipyridine, and co-cultured at 4 o C (Lesic and Carniel 2005). Several acceptor or donor strains were selected to increase the possibility on horizontally transfer of HPI between these strains.…”