Erwinia chrysanthemi requires a second iron transport route dependent of the siderophore achromobactin for extracellular growth and plant infection.
Full virulence of the pectinolytic enterobacterium Erwinia chrysanthemi strain 3937 depends on the production in planta of the catechol-type siderophore chrysobactin. Under iron-limited conditions, E. chrysanthemi synthesizes a second siderophore called achromobactin belonging to the hydroxy/carboxylate class of siderophore. In this study, we cloned and functionally characterized a 13 kb long operon comprising seven genes required for the biosynthesis (acs) and extracellular release (yhcA) of achromobactin, as well as the gene encoding the specific outer membrane receptor for its ferric complex (acr). The promoter of this operon was negatively regulated by iron. In a fur null mutant, transcriptional fusions to the acsD and acsA genes were constitutively expressed. Band shift assays showed that the purified E. chrysanthemi Fur repressor protein specifically binds in vitro to the promoter region of the acsF gene confirming that the metalloregulation of the achromobactin operon is achieved directly by Fur. The temporal production of achromobactin in iron-depleted bacterial cultures was determined: achromobactin is produced before chrysobactin and its production decreases as that of chrysobactin increases. Pathogenicity tests performed on African violets showed that achromobactin production contributes to the virulence of E. chrysanthemi. Thus, during infection, synthesis of these two different siderophores allows E. chrysanthemi cells to cope with the fluctuations of iron availability encountered within plant tissues. Interestingly, iron transport mediated by achromobactin or a closely related siderophore probably exists in other phytopathogenic bacterial species such as Pseudomonas syringae.
Franza
Thierry
T
Laboratoire de Pathologie Végétale, UMR 217 INRA/INA P-G/UPMC, 16 rue Claude Bernard, 75005 Paris, France.
Mahé
Bruno
B
Expert
Dominique
D
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D002951:Citrates / Q000096:biosynthesis / Q000502:physiology*; D003001:Cloning, Molecular; D016974:Dickeya chrysanthemi / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D058085:Iron Compounds / Q000378:metabolism*; D007656:Ketoglutaric Acids; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D009876:Operon; D010935:Plant Diseases / Q000382:microbiology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D017262:Siderophores / Q000502:physiology*; D032413:Viola / Q000382:microbiology; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000502:physiology
D001426:Bacterial Proteins; D002951:Citrates; D058085:Iron Compounds; D007656:Ketoglutaric Acids; D012097:Repressor Proteins; D017262:Siderophores; D037521:Virulence Factors; C413577:achromobactin; C068477:ferric uptake regulating proteins, bacterial