Siderophore-mediated iron transport correlates with the presence of specific iron-regulated proteins in the outer membrane of Rhizobium meliloti.
A universal chemical assay used to detect the production of siderophores in a range of Rhizobium strains showed that production is strain specific. Iron nutrition bioassays carried out on Rhizobium meliloti strains to determine cross-utilization of their siderophores showed that R. meliloti 2011, 220-5, and 220-3 could each use the siderophores produced by the other two but not the siderophore produced by R. meliloti DM4 (and vice versa). Mutants of R. meliloti 2011 and 220-5 defective in siderophore production were isolated by Tn5-mob mutagenesis. The Tn5-mob-containing EcoRI fragment of mutant R. meliloti 220-5-1 was cloned into pUC19. By using this fragment as a probe, the presence of a homologous region was observed in R. meliloti 2011 and 220-3 but not in R. meliloti DM4. A complementing cosmid from a gene bank of R. meliloti 2011 was identified by using the same probe. Introduction of this cosmid into R. meliloti 102F34, a strain not producing a siderophore, resulted in the ability of this strain to produce a siderophore and also in the ability to utilize the siderophores produced by R. meliloti 2011, 220-5, and 220-3 but not the siderophore produced by R. meliloti DM4. A comparative analysis of the outer membrane proteins prepared from iron-deficient cultures of R. meliloti 102F34 and 102F34 harboring the cosmid revealed the presence, in the latter, of a low-iron-induced outer membrane protein corresponding to a low-iron-induced protein in R. meliloti 2011, 220-5, and 220-3. This protein is not present in R. meliloti DM4. The results suggest that R. meliloti 2011, 220-5, and 220-3 produce siderophores that are identical or sufficiently similar in structure to be transported by the membrane transport system of each strain while also indicating that utilization of a particular siderophore is correlated with the presence of specific outer membrane proteins.
Reigh
G
G
School of Biological Sciences, Dublin City University, Glasnevin, Ireland.
O'Connell
M
M
D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D003360:Cosmids / Q000235:genetics; D015342:DNA Probes; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D005816:Genetic Complementation Test; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D016254:Mutagenesis, Insertional; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D017262:Siderophores / Q000235:genetics / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity
D001425:Bacterial Outer Membrane Proteins; D015342:DNA Probes; D017262:Siderophores; D007501:Iron