Premium
The Rhizobium leguminosarum tonB gene is required for the uptake of siderophore and haem as sources of iron
Author(s) -
Wexler Margaret,
Yeoman Kay H.,
Stevens James B.,
De Luca Nicola G.,
Sawers Gary,
Johnston Andrew W. B.
Publication year - 2001
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2001.02556.x
Subject(s) - biology , operon , siderophore , mutant , rhizobium leguminosarum , gene , bacteria , transcription (linguistics) , rhizobium , escherichia coli , gene product , genetics , pathogenicity island , biochemistry , gene expression , rhizobiaceae , symbiosis , linguistics , philosophy
In the N 2 ‐fixing bacterium Rhizobium leguminosarum , mutations in a homologue of tonB ( tonB Rl ) block the import of vicibactin and haem as iron sources in free‐living bacteria. TonB Rl mutants were normal for growth with ferric dicitrate and slightly reduced for growth with haemoglobin as sole iron sources. The deduced TonB Rl product is larger than that of (for example) Escherichia coli , on account of an extended N‐terminal domain. Transcription of tonB Rl was enhanced in low‐Fe growth conditions; this was not controlled by Fur, nor RpoI, an Fe‐regulated extracytoplasmic σ factor. Upstream of tonB Rl and transcribed divergently is an operon, hmuPSTUV , whose products are homologous to ABC transporters involved in haem uptake in pathogenic bacteria. Expression of hmuPSTUV was enhanced in low‐Fe conditions, and hmu mutants show slightly diminished growth on haem as sole Fe source, suggesting that there is more than one system for the uptake of this molecule. hmuPSTUV expression appears to be from three closely linked promoters. Downstream of hmuPSTUV , a gene that may encode an extracytoplasmic σ factor was identified, but this gene, rpoZ , did not affect the transcription of tonB Rl or hmuPSTUV . Mutations in tonB Rl , hmu genes and rpoZ did not affect symbiotic N 2 fixation in peas.