The Bradyrhizobium japonicum fegA gene encodes an iron-regulated outer membrane protein with similarity to hydroxamate-type siderophore receptors

LeVier, Kristin; Guerinot, Mary Lou

doi:10.1128/jb.178.24.7265-7275.1996

Cited by 35 publications

(19 citation statements)

References 88 publications

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“…Ferric siderophore receptors are part of a high-affinity iron transport system that takes up iron chelates from the environment. The only B. japonicum ferric siderophore receptor characterized to date is FegA, a receptor for the fungal siderophore ferrichrome observed in strain 61A152 that is required for symbiosis with soybean (3,15). In the present study, we provide evidence that Irr is a direct positive regulator of ferric siderophore receptor gene expression and that it occupies the promoters of those genes in vivo.…”

supporting

confidence: 52%

Positive Control of Ferric Siderophore Receptor Gene Expression by the Irr Protein inBradyrhizobium japonicum

et al. 2009

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supporting

confidence: 52%

Positive Control of Ferric Siderophore Receptor Gene Expression by the Irr Protein inBradyrhizobium japonicum

et al. 2009

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“…It also may indicate that direct repression by the Fur protein is less common in B. japonicum than, e.g., in E. coli or Bacillus subtilis (4,39). The sole B. japonicum target gene for which this regulatory function of Fur has been well documented is the irr gene (13), and only indirect evidence suggests Fur-dependent repression also at the hemA (25) and the fegA genes (34). This situation is reminiscent to that in R. leguminosarum and Sinorhizobium meliloti, where RirA, and not Fur, is the general iron regulator (59,62).…”

Section: Vol 188 2006 Iron-controlled Gene Expression In B Japonicmentioning

confidence: 96%

The Iron Control Element, Acting in Positive and Negative Control of Iron-RegulatedBradyrhizobium japonicumGenes, Is a Target for the Irr Protein

Rudolph¹,

Semini²,

Hauser³

et al. 2006

J Bacteriol

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Bradyrhizobium japonicum, the nitrogen-fixing soybean symbiont, possesses a heme uptake system encoded by the gene cluster hmuVUT-hmuR-exbBD-tonB. Transcription of the divergently oriented hmuT and hmuR genes was previously found to be induced by iron limitation and to depend on a 21-bp promoter-upstream iron control element (ICE). Here, we show by deletion analysis that the full-length ICE is needed for this type of positive control. Additional genes associated with ICE-like motifs were identified in the B. japonicum genome, of which bll6680 and blr7895 code for bacterioferritin and rubrerythrin homologs, respectively. Transcription start site mapping revealed that their ICEs directly overlap with either the ؊10 promoter region or the transcription initiation site, suggesting an involvement of the ICE in negative control of both genes. Consistent with this inference was the observed downregulation of both genes under iron limitation, which in the case of bll6680 was shown to require an intact ICE motif. Using a yeast one-hybrid system, we demonstrated in vivo interaction of the iron response regulator (Irr) with all three ICEs. Moreover, specific in vitro binding of purified Irr protein to the ICE motifs of bll6680 and blr7895 was shown in electrophoretic mobility shift experiments. A genome-wide survey for iron-regulated genes with a custom-made Affymetrix gene chip revealed 17 genes to be induced and 68 to be repressed under iron-replete conditions. Remarkably, ICE-like motifs are associated with a large subset of those B. japonicum genes. We propose the ICE as an important cis-acting element in B. japonicum which represents the DNA-binding site for the Irr protein and, depending on its location within promoter regions, is involved in positive or negative control of the associated iron-regulated genes.

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“…1). A 79 kDa iron regulated outer membrane protein was found to be present in the outer membrane protein preparation of ST1pFJ12 which correlated with the FegA protein of B. japonicum 61A152 [30] and was absent in the parent strain ST1 (Fig. 2).…”

Section: Resultsmentioning

confidence: 97%

“…Iron supplemented medium was prepared by adding 100 µM FeCl 3 to the above medium. The medium as described by Winkelmann was used for siderophore production by U. maydis and Rhodotorula mucilaginosa MTCC 850 [31] P. fluorescens ATCC13525, P. aeruginosa MTCC2453 and P. putida KT2440 were from our laboratory collection; Nitrogen-fixing Glycine max (soybean) symbiont [30] ST1pFJ12 ST1 carrying pFJ Present study Escherichia coli: DH5α hsdR17 endA1 thi-1 gyrA96 relA1 supE44 ∆lac [38] U169 (φ80dlacZ∆M15) S17.1 hsdR pro recA containing RP-4-2-Tc:: Mu integration into chromosome [39] S17.1pFJ E. coli S17. Escherichia-Pseudomonas shuttle vector pUCP19, [37] containing the mob fragment pFJ pUCPM18-Gm with fegA cloned in Present study XbaI-BamHI site positive for siderophore production and their supernatants at the end of 48 h of growth under iron limiting condition was used as sources of siderophores.…”

Section: Bacterial Strains Plasmids and Growth Conditionsmentioning

confidence: 99%

Enhanced Survival and Nodule Occupancy of Pigeon pea Nodulating Rhizobium sp. ST1 expressing fegA Gene of Bradyrhizobium japonicum 61A152

Joshi¹,

Desai²,

Archana³

et al. 2009

OnLine J. of Biological Sciences

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Problem statement: Rhizobial isolates belonging to genera (Rhizobium sp. and Mesorhizobium sp.) in our laboratory produced only catecholate type of siderophores. Although FhuA and FegA (ferrichrome receptors) homologs were found to be present in the sequenced genomes of few rhizobia (e.g., 1 in R. etli and 2 in Mesorhizobium sp. BNC1), laboratory isolates of the corresponding genera failed to utilize ferrichrome, a siderophore which is present in nanomolar concentrations in the soil. This inability was considered as a negative fitness factor with respect to rhizospheric colonization by these rhizobia. Approach: The 2.4 kb fegA gene (encoding ferrichrome receptor) was amplified along with its native promoter from Bradyrhizobium japonicum 61A152 and cloned in a broad host range plasmid vector pUCPM18. The plasmid construct pFJ was transferred by conjugation into Rhizobium sp. ST1 to give transconjugant ST1pFJ12. The consequence of FegA expression on the transconjugant was tested under lab and soil conditions, using physiological experiments. Results: Ability of the transconjugant ST1pFJ12 to utilize ferrichrome and expression of a 79 kD protein band on the outer membrane of the transconjugant confirmed FegA expression. Transconjugant ST1pFJ12 exhibited increased growth rate as compared to the parent strain ST1, in minimal media containing ferrichrome as the sole iron source, confirming the positive effect of FegA expression. Inoculation of pigeon pea seedlings with transconjugant ST1pFJ12 led to a marked increase in plant growth parameters as compared to plants inoculated with the parent strain ST1, the effect being more pronounced when Ustilago maydis, a ferrichrome producer was co-inoculated in the systems. Nodule occupancy on pigeon pea plant when inoculated with the transconjugant ST1pFJ12 alone was 57% which increased to 66% when co-inoculated with U. maydis as compared with 37 and 30% respectively, seen with parental strain ST1 inoculation. Conclusion: The clear increase in nodule occupancy and higher rhizospheric colonization by the fegA transconjugants, presented in this study together with the previous research reported from our laboratory, led us to conclude that ferrichrome utilization ability played an important role in the rhizospheric colonization of the bioinoculant strains. Testing the ability to utilize hydroxamate siderophores therefore, holds prime importance in selecting an efficient biofertilizer strain.

show abstract

The Bradyrhizobium japonicum fegA gene encodes an iron-regulated outer membrane protein with similarity to hydroxamate-type siderophore receptors

Abstract: Iron is important in the symbiosis between soybean and its nitrogen-fixing endosymbiont

Cited by 35 publications

References 88 publications

Positive Control of Ferric Siderophore Receptor Gene Expression by the Irr Protein inBradyrhizobium japonicum

Positive Control of Ferric Siderophore Receptor Gene Expression by the Irr Protein inBradyrhizobium japonicum

The Iron Control Element, Acting in Positive and Negative Control of Iron-RegulatedBradyrhizobium japonicumGenes, Is a Target for the Irr Protein

Enhanced Survival and Nodule Occupancy of Pigeon pea Nodulating Rhizobium sp. ST1 expressing fegA Gene of Bradyrhizobium japonicum 61A152

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