Common and specific characteristics of the high-pathogenicity island of Yersinia enterocolitica

Abstract

Yersinia pestis, Y. pseudotuberculosis O:1, and Y. enterocolitica biogroup 1B strains carry a high-pathogenicity island (HPI), which mediates biosynthesis and uptake of the siderophore yersiniabactin and a mouse-lethal phenotype. The HPI of Y. pestis and Y. pseudotuberculosis (Yps HPI) are highly conserved in sequence and organization, while the HPI of Y. enterocolitica (Yen HPI) differs significantly. The 43,393-bp Yen HPI sequence of Y. enterocolitica WA-C, serotype O:8, was completed and compared to that of the Yps HPI of Y. pseudotuberculosis PB1, serotype O:1A. A common GC-rich region (G+C content, 57.5 mol%) of 30.5 kb is conserved between yersinia strains. This region carries genes for yersiniabactin biosynthesis, regulation, and uptake and thus can be considered the functional "core" of the HPI. In contrast, the second part of the HPI is AT rich and completely different in two evolutionary lineages of the HPI, being 12.8 kb in the Yen HPI and 5.6 kb in the Yps HPI. The variable part acquired one IS100 element in the Yps HPI and accumulated four insertion elements, IS1328, IS1329, IS1400, and IS1222, in the Yen HPI. The insertion of a 125-bp ERIC sequence modifies the structure of the promoter of the ybtA yersiniabactin regulator in the Yen HPI. In contrast to the precise excision of the Yps HPI in Y. pseudotuberculosis, the Yen HPI suffers imprecise deletions. The Yen HPI is stably integrated in one of the three asn tRNA copies in Y. enterocolitica biogroup 1B (serotypes O:8, O:13, O:20, and O:21), probably due to inactivation of the putative integrase. The 17-bp duplications of the 3' end of the asnT RNA are present in both Yersinia spp. The HPI attachment site is unoccupied in nonpathogenic Y. enterocolitica NF-O, biogroup 1A, serotype O:5. The HPI of Yersinia is a composite and widely spread genomic element with a highly conserved yersiniabactin functional "core" and a divergently evolved variable part.

FIG. 1

Complete structure of the HPI in Y. enterocolitica WA-C. The Left (5′) (A) and right (3′) (B) ends of the island are shown. Arrows show the positions of the ORFs and the direction of transcription. Positions of restriction sites are depicted by vertical lines; numbers above the lines show the distance from the beginning of the sequenced DNA fragment in base pairs.

FIG. 2

Complete structure and the G+C content of the HPIs in Y. pseudotuberculosis PB1 and Y. enterocolitica WA-C. Arrows below the graph show position of genes and direction of transcription. Vertical arrows show the borders of the HPI, the left DR₁₇ within asn tRNA defines the left border, and the right DR₁₇ defines the right border.

FIG. 3

Insertion of a 125-bp ERIC sequence into the ybtA promoter of the Yen HPI. The upper panel shows the structure of the ybtA promoter in Y. pestis and Y. enterocolitica. The lower panel depicts aligned nucleotide sequences of both promoters. Identical bases are boxed in grey. Black arrows show two repeated sequences (RS1 and RS2) of the ybtA promoter. The asterisk in the RS2* sequence depicts an interruption in the repeated sequence. Open arrows show the position and direction of the inverted repeats (IR) of the ERIC. Yen WA-C, Y. enterocolitica WA-C; Yp KIM, Y. pestis KIM; FBS, Fur protein-binding site; RS, repeated sequences, SD, potential ribosome-binding site.

FIG. 4

Fragment of the Y. pseudotuberculosis PB1 chromosome with the 3′ end of the Yps HPI. The large arrow on the left indicates the position of fyuA. Arrows show positions of the ORFs and their direction of transcription. Black bars within the Y. pseudotuberculosis sequence represent regions of identity with the Y. enterocolitica DNA. Triangles indicate positions of the IS elements within the Yen HPI. PstI, EcoRI, BamHI, and KpnI depict the positions of recognition sites of the corresponding enzymes. Small black arrows under the graph indicate PCR primers used. The DIG–11-dUTP-labelled PCR products obtained with the same primer pairs were used as hybridization probes. + and −, presence or absence, respectively, of hybridization products. +*, larger PCR amplicon in Y. enterocolitica WA-C; Y.ent, Y. enterocolitica; Y.pstbc, Y. pseudotuberculosis.

FIG. 5

Left (5′) and right (3′) junctions of the Yen HPI. Arrows in the graph show position and orientation of the genes. Black arrows under the graph show PCR primers used. The + and − indicate the presence or absence of a PCR product amplified with W250 plus W598 and asn468 plus c15-205 primer pairs. Numbers correspond to the size of the PCR products in base pairs. Y.ent, Y. enterocolitica.

FIG. 6

Unoccupied attachment site of the HPI in Y. enterocolitica NF-O. The NF-O sequence was amplified with primers W250 and Ye262 (Fig. 5) and aligned with the 5′ and 3′ boundaries of the Yen HPI. Grey boxes show identical nucleotide sequences and a 16-bp part of the DR₁₇. Numbers on the right show relative positions of nucleotides in base pairs. 5′ end, 5′ boundary of the Yen HPI, asnT RNA; 3′ end, 3′ boundary of the Yen HPI; NF-O, a PCR product amplified by the W250 and Ye262 primers in Y. enterocolitica NF-O.