Structural and functional analysis of the riboflavin synthesis genes encoding GTP cyclohydrolase II (ribA), DHBP synthase (ribBA), riboflavin synthase (ribC), and riboflavin deaminase/reductase (ribD) from Helicobacter pylori strain P1

The functions of the riboflavin synthesis gene homologues ribA, ribBA, ribC , and ribD from Helicobacter pylori strain P1 were confirmed by complementa tion of defined Escherichia coli mutant strains. The H. pylori ribBA gene, which is similar to bifunctional ribBA genes of Gram-positive bacteria, ful ly complemented the ribB mutation and partially restored growth in a ribC m utant. However, ribBA did not complement the ribA mutation in E. coli, thus explaining the presence of the additional separate copy of the ribA gene i n the H. pylori chromosome. In E. coli exclusively ribA conferred hemolytic activity and gave rise to production of molecules with fluorescence charac teristics similar to flavins, as observed earlier. The E. coli hemolysin Cl yA was not involved in causing the hemolytic phenotype. No riboflavin synth esis genes on plasmids conferred iron uptake functions to a siderophore-def icient mutant of E. coli. Marker exchange mutagenesis of the genes in H. py lori was not successful indicating that riboflavin synthesis is essential f or basic metabolic functions of the gastric pathogen. (C) 2000 Federation o f European Microbiological Societies. Published by Elsevier Science B.V. Al l rights reserved.