Genomic-sequence comparison of two unrelated isolates of the human gastricpathogen Helicobacter pylori

Helicobacter pylori, one of the most common bacterial pathogens of humans, colonizes the gastric mucosa, where it appears to persist throughout the ho st's life unless the patient is treated. Colonization induces chronic gastr ic inflammation which can progress to a variety of diseases, ranging in sev erity from superficial gastritis and peptic ulcer to gastric cancer and muc osal-associated lymphoma(1). Strain-specific genetic diversity has been pro posed to be involved in the organism's ability to cause different diseases or even be beneficial to the infected host(2,3) and to participate in the l ifelong chronicity of infection(4). Here we compare the complete genomic se quences of two unrelated H. pylori isolates. This is, to our knowledge, the first such genomic comparison. H. pylori was believed to exhibit a large d egree of genomic and allelic diversity, but we find that the overall genomi c organization, gene order and predicted proteomes (sets of proteins encode d by the genomes) of the two strains are quite similar, Between 6 to 7% of the genes are specific to each strain, with almost half of these genes bein g clustered in a single hypervariable region.