Affiliation:
1. School of Biotechnology, Dublin City University, Dublin 9, Ireland1;
2. Max Planck Institute for Molecular Genetics, D14195 Berlin, Germany2; and
3. Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201-30983
Abstract
ABSTRACT
Eight genes have been identified that function in the regulation, biosynthesis, and transport of rhizobactin 1021, a hydroxamate siderophore produced under iron stress by
Sinorhizobium meliloti
. The genes were sequenced, and transposon insertion mutants were constructed for phenotypic analysis. Six of the genes, named
rhbABCDEF
, function in the biosynthesis of the siderophore and were shown to constitute an operon that is repressed under iron-replete conditions. Another gene in the cluster, named
rhtA
, encodes the outer membrane receptor protein for rhizobactin 1021. It was shown to be regulated by iron and to encode a product having 61% similarity to IutA, the outer membrane receptor for aerobactin. Transcription of both the
rhbABCDEF
operon and the
rhtA
gene was found to be positively regulated by the product of the eighth gene in the cluster, named
rhrA
, which has characteristics of an AraC-type transcriptional activator. The six genes in the
rhbABCDEF
operon have interesting gene junctions with short base overlaps existing between the genes. Similarities between the protein products of the biosynthesis genes and other proteins suggest that rhizobactin 1021 is synthesized by the formation of a novel siderophore precursor, 1,3-diaminopropane, which is then modified and attached to citrate in steps resembling those of the aerobactin biosynthetic pathway. The cluster of genes is located on the pSyma megaplasmid of
S. meliloti
2011. Reverse transcription-PCR with RNA isolated from mature alfalfa nodules yielded no products for
rhbF
or
rhtA
at a time when the
nifH
gene was strongly expressed, indicating that siderophore biosynthesis and transport genes are not strongly expressed when nitrogenase is being formed in root nodules. Mutants having transposon insertions in the biosynthesis or transport genes induced effective nitrogen-fixing nodules on alfalfa plants.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Reference54 articles.
1. Gapped BLAST and PSI-BLAST: a new generation of protein database search programs
2. Leghemoglobin and Rhizobium respiration;Appleby C. A.;Annu. Rev. Plant Physiol.,1984
3. Intricacies of ribosomal frameshifting;Atkins J. F.;Nat. Struct. Biol.,1999
4. Ausubel
F. M.
Brent
R.
Kingston
R. E.
Moore
D. D.
Seidman
J. G.
Smith
J. A.
Struhl
K.
Current protocols in molecular biology.
1996
John Wiley & Sons Inc.
New York N.Y
5. High-Resolution Physical Map of the
Sinorhizobium meliloti
1021 pSyma Megaplasmid
Cited by
173 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献