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Category: Bacterial Pathogenesis; Clinical Microbiology
Mechanisms and Regulation of Iron Uptake in the Rhizobia, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap30-1.gif /docserver/preview/fulltext/10.1128/9781555816544/9781555812928_Chap30-2.gifAbstract:
This chapter considers only recent experimental and in silico analyses that directly apply to the iron biology of rhizobia. At least two main sets of observations have emerged from these studies and are recurring themes in the chapter. The first is that the rhizobia have great flexibility in their use of iron sources compared to many other bacteria. The second is that some paradigms of iron-responsive gene regulation do not operate in the rhizobia or, at least, not all rhizobia. There have been detailed biochemical and genetic studies of only two rhizobial siderophores. These are the trihydroxamate vicibactin (VB), made by most strains of Rhizobium leguminosarum, and the chemically distinct dihydroxamate rhizobactin 1021 (RB1021), synthesized by different strains of S. meliloti, including the well-characterized strain 1021—hence the name RB1021. The expression of bacterial genes involved in iron uptake and other aspects of “iron biology” responds to iron availability, and the rhizobia are no exception. It is clear that the rhizobia have great flexibility for iron uptake and show real differences in their iron-responsive gene regulation compared to other gram-negative bacteria. Importantly, it is now evident that as much as 50% of the genome of one rhizobial species does not resemble those of other, even closely related species (e.g., Sinorhizobium meliloti and R. leguminosarum). Focusing on mechanisms of iron uptake, these lines of argument may explain why rhizobia not only use siderophores but also contain at least two transport systems more frequently associated with pathogens.
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Structures of three chemically characterized siderophores made by rhizobia.
Structures of three chemically characterized siderophores made by rhizobia.
Organization of gene clusters involved in siderophore synthesis and uptake in R. leguminosarum and S. meliloti. Relative locations of genes for the synthesis and uptake of the siderophores VB by R. leguminosarum (a) and RB1021 by S. meliloti (b) are shown. Dotted lines indicate transcriptional organization of the different operons. Gene functions are given in the text, Table 2 , and Fig. 3 and 4 . Data from Carter et al. (2002) for VB and from Lynch et al. (2001) for RB1021.
Organization of gene clusters involved in siderophore synthesis and uptake in R. leguminosarum and S. meliloti. Relative locations of genes for the synthesis and uptake of the siderophores VB by R. leguminosarum (a) and RB1021 by S. meliloti (b) are shown. Dotted lines indicate transcriptional organization of the different operons. Gene functions are given in the text, Table 2 , and Fig. 3 and 4 . Data from Carter et al. (2002) for VB and from Lynch et al. (2001) for RB1021.
Pathway of VB synthesis. The proposed pathway for VB synthesis in R. leguminosarum is shown. The numbered steps correspond to those in Table 2 . Adapted from Carter et al. (2002) .
Pathway of VB synthesis. The proposed pathway for VB synthesis in R. leguminosarum is shown. The numbered steps correspond to those in Table 2 . Adapted from Carter et al. (2002) .
Pathway of RB1021 synthesis. The proposed pathway for RB1021 synthesis in S. meliloti is shown. Adapted from Lynch et al. (2001) .
Pathway of RB1021 synthesis. The proposed pathway for RB1021 synthesis in S. meliloti is shown. Adapted from Lynch et al. (2001) .
Phylogenic tree of the Fur superfamily in the rhizobia, compared with homologues in other bacterial taxa. A maximum-parsimony phylogenetic tree was constructed from amino acid sequences of Fur and Fur-like sequences by using PAUP* version 4.0b10. The tree is rooted at the midpoints, and bootstrap values are shown for nodes with values of >70. Branch lengths are proportional to the degree of amino acid change. Proteins were obtained from the GenBank database. A.ae, Aquifex aeolicus; A.tum, Agrobacterium tumefaciens; B.jap, Bradyrhizobium japonicum; B.sub, Bacillus subtilis; B.hen, Bartonella henselae; B.mel, Brucella melintensis; B.per, Bordetella pertussis; C.ac, Clostridium acetobutylicum; C.cre, Caulobacter crescentus; D.vu, Desulfovibrio vulgaris; E.col, Escherichia coli K-12; H.inf, Haemophilus influenzae; H.pyl, Helicobacter pylori; K.pne, Klebsiella pneumoniae; L.pne, Legionella pneumophila; L.inn, Listeria innocua; M.lot, Mesorhizobium loti; N.men, Neisseria meningitidis; P.aer, Pseudomonas aeruginosa; P.mul, Pasteurella multocida; R.leg, Rhizobium leguminosarum, R.sph, Rhodobacter sphaeroides; R.pa, Rhodopseudomonas palustris; S.ent, Salmonella enterica; S.mel, Sinorhizobium meliloti, S.typ, Salmonella enterica serovar Typhimurium; S.aur, Staphylococcus aureus; T.mar, Thermotoga maritima; V.ang, Vibrio anguillarum; V.cho, Vibrio cholerae; Y.pes, Yersinia pestis. Proteins from Agrobacterium, Brucella, Mesorhizobium, Rhizobium, and Sinorhizobium are marked with stars.
Phylogenic tree of the Fur superfamily in the rhizobia, compared with homologues in other bacterial taxa. A maximum-parsimony phylogenetic tree was constructed from amino acid sequences of Fur and Fur-like sequences by using PAUP* version 4.0b10. The tree is rooted at the midpoints, and bootstrap values are shown for nodes with values of >70. Branch lengths are proportional to the degree of amino acid change. Proteins were obtained from the GenBank database. A.ae, Aquifex aeolicus; A.tum, Agrobacterium tumefaciens; B.jap, Bradyrhizobium japonicum; B.sub, Bacillus subtilis; B.hen, Bartonella henselae; B.mel, Brucella melintensis; B.per, Bordetella pertussis; C.ac, Clostridium acetobutylicum; C.cre, Caulobacter crescentus; D.vu, Desulfovibrio vulgaris; E.col, Escherichia coli K-12; H.inf, Haemophilus influenzae; H.pyl, Helicobacter pylori; K.pne, Klebsiella pneumoniae; L.pne, Legionella pneumophila; L.inn, Listeria innocua; M.lot, Mesorhizobium loti; N.men, Neisseria meningitidis; P.aer, Pseudomonas aeruginosa; P.mul, Pasteurella multocida; R.leg, Rhizobium leguminosarum, R.sph, Rhodobacter sphaeroides; R.pa, Rhodopseudomonas palustris; S.ent, Salmonella enterica; S.mel, Sinorhizobium meliloti, S.typ, Salmonella enterica serovar Typhimurium; S.aur, Staphylococcus aureus; T.mar, Thermotoga maritima; V.ang, Vibrio anguillarum; V.cho, Vibrio cholerae; Y.pes, Yersinia pestis. Proteins from Agrobacterium, Brucella, Mesorhizobium, Rhizobium, and Sinorhizobium are marked with stars.
Species of rhizobia referred to in this chapter
Species of rhizobia referred to in this chapter
Proposed functions of individual vbs genes in the VB biosynthetic gene cluster of R. leguminosarum
Proposed functions of individual vbs genes in the VB biosynthetic gene cluster of R. leguminosarum
Similarities among the Fbp-like proteins of rhizobia and selected homologues in other taxa.
Similarities among the Fbp-like proteins of rhizobia and selected homologues in other taxa.