EVIDENCE FOR 2 EVOLUTIONARY LINEAGES OF HIGHLY PATHOGENIC YERSINIA SPECIES

Sensitivity to Yersinia pestis bacteriocin pesticin correlates with th e existence of two groups of human pathogenic yersiniae, mouse lethal and mouse nonlethal. The presence of the outer membrane pesticin recep tor (FyuA) in mouse-lethal yersiniae is a prerequisite for pesticin se nsitivity. Genes that code for FyuA (fyuA) were identified and sequenc ed from pesticin-sensitive bacteria, including Y. enterocolitica bioty pe 1B (serotypes O8, O13, O20, and O21), Y. pseudotuberculosis serotyp e O1, Y. pestis, two known pesticin-sensitive Escherichia coli isolate s (E. coli Phi and E. coli CA42), and two newly discovered pesticin-se nsitive isolates, E. coli K49 and K235. A 2,318-bp fyuA sequence was s hown to be highly conserved in all pesticin-sensitive bacteria, includ ing E. coli strains (DNA sequence homology was 98.5 to 99.9%). The sam e degree of DNA homology (97.8 to 100%) was established for the sequen ced 276-bp fragment of the irp2 gene that encodes high-molecular-weigh t protein 2, which is also thought to be involved in the expression of virulence by Yersinia species. Highly conserved irp2 was also found i n all pesticin-sensitive E. coli strains. On the basis of the fyuA and irp2 sequence homologies, two evolutionary groups of highly pathogeni c Yersinia species can be established. One group includes Y. enterocol itica biotype 1B strains, while the second includes Y. pestis, Y. pseu dotuberculosis serotype O1, and irp2-positive Y. pseudotuberculosis se rotype O3 strains, E. coli Phi, CA42, K49, and K235 belong to the seco nd group. The possible proximity of these two iron-regulated genes (fy uA and irp2), as well as their high levels of sequence conservation an d similar G+C contents (56.2 and 59.8 mol%), leads to the assumption t hat these two genes may represent part of an unstable pathogenicity is land that has been acquired by pesticin-sensitive bacteria as a result of a horizontal transfer.