Despite recent advances in our understanding of how
Helicobacter pyloricauses disease, the factors that allow this pathogen to persist in the stomach have not yet been fully characterized. To identify new virulence factors in H. pylori, we generated low-infectivity variants of a mouse-colonizing H. pyloristrain using the classical technique of in vitroattenuation. The resulting variants and their highly infectious progenitor bacteria were then analyzed by global gene expression profiling. The gene expression levels of five open reading frames (ORFs) were significantly reduced in low-infectivity variants, with the most significant changes observed for ORFs HP1583 and HP1582. These ORFs were annotated as encoding homologs of the Escherichia colivitamin B6biosynthesis enzymes PdxA and PdxJ. Functional complementation studies with E. coliconfirmed H. pyloriPdxA and PdxJ to be bona fidehomologs of vitamin B6biosynthesis enzymes. Importantly, H. pyloriPdxA was required for optimal growth in vitroand was shown to be essential for chronic colonization in mice. In addition to having a well-known metabolic role, vitamin B6is necessary for the synthesis of glycosylated flagella and for flagellum-based motility in H. pylori. Thus, for the first time, we identify vitamin B6biosynthesis enzymes as novel virulence factors in bacteria. Interestingly, pdxAand pdxJorthologs are present in a number of human pathogens, but not in mammalian cells. We therefore propose that PdxA/J enzymes may represent ideal candidates for therapeutic targets against bacterial pathogens. IMPORTANCEApproximately half of the world’s population is infected with H. pylori, yet how H. pyloribacteria establish chronic infections in human hosts remains elusive. From gene array studies, we identified two genes as representing potentially novel colonization factors for H. pylori. These genes encoded enzymes involved in the synthesis of vitamin B6, an important molecule for many metabolic reactions in living organisms. Little is currently known regarding vitamin B6biosynthesis in human pathogens. We showed that mutant H. pyloribacteria lacking an enzyme involved in de novovitamin B6biosynthesis, PdxA, were unable to synthesize motility appendages (flagella) and were unable to establish chronic colonization in mice. Thus, this work identifies vitamin B6biosynthesis enzymes as novel virulence factors for bacterial pathogens. Interestingly, a number of human pathogens, but not their mammalian hosts, possess these genes, which suggests that Pdx enzymes may represent ideal candidates for new therapeutic targets.