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Establishing a successful infection within the gastric environment and its varied and changing niches requires adaptation achieved through regulation of bacterial gene expression. In the gastric environment in addition to the low pH Helicobacter pylori is required to adapt to conditions of iron limitation. In this study, we used cDNA microarrays to identify genes whose expression was altered when the bacterium was grown under differing conditions of pH (5 versus 7) and iron limitation. cDNA microarray analyses following exposure to different growth conditions were carried out for three H. pylori strains 26695 (gastritis-associated), J99 (ulcer-associated) and AG-1 (atrophic gastritis-associated). Genes were identified whose expression was acid pH-dependent in all the strains: 68 genes were up-regulated, these included urease-related genes (ureA, ureB, ureI, UreF), amidase (aimE) and genes involved in flagellar synthesis (flgB, fliM, flgE). Additionally, up-regulation of transport-related genes and genes encoding binding proteins (glnQ, glnH, exbD) were noted. Furthermore, 37 genes were down-regulated from different functional groups (e.g., outer membrane proteins and chaperones). At pH 7, iron limitation mainly induced motility-associated genes, whereas at pH5, iron depletion although inducing down-regulation of 12 genes, led to the increased expression of 21 genes including those coding for carbonic anhydrase and proteins involved in metal ion transport, instead of genes coding for urease and amidase enzymes. Genes encoding virulence factors (e.g., cagA and vacA) and proteins involved in motility were over-expressed under all the conditions of stress. Collectively, as effectors of the H. pylori stress response, this transcriptome analysis implicating up-regulation of various metal responsive regulators and metal transport-related genes, in addition to induction of ammonia-producing enzymes and virulence factors (CagA and VacA), emphasizes the link between the bacterial response to acidity, metal metabolism and virulence. Moreover, this response was similar in H. pylori strains associated with different pathologies.&#xd;&#xa

HP-23: Co-ordinated Regulation of Gene Expression in H. Pylori in Response to Low pH and Iron Limiting Growth Conditions