Perception and Homeostatic Control of Iron in the Rhizobia and Related Bacteria

• Published in: Annual review of microbiology Vol. 69; no. 1; pp. 229 - 245
• Main Author: O'Brian, Mark R
• Format: Journal Article
• Language: English
• Published: United States Annual Reviews 15-10-2015; Annual Reviews, Inc
• Subjects: Alphaproteobacteria - classification; Alphaproteobacteria - physiology; Bacterial Proteins - metabolism; Biosynthesis; E coli; Eukaryotes; Gene expression; heme; Heme - biosynthesis; Homeostasis; Iron; Iron - metabolism; iron export; Manganese; Manganese - metabolism; Metabolism; Microbiology; Oxidative Stress; Proteolysis; Rhizobium - physiology; Transcription Factors - metabolism; transcriptional control; iron export; transcriptional control; heme; manganese; oxidative stress
• ISSN: 0066-4227; 1545-3251
• DOI: 10.1146/annurev-micro-091014-104432

Iron is an essential nutrient, but it can also be toxic. Therefore, iron homeostasis must be strictly regulated. Transcriptional control of iron-dependent gene expression in the rhizobia and other taxa of the
Alphaproteobacteria
is fundamentally different from the Fur paradigm in
Escherichia coli
and other model systems. Rather than sense iron directly, the rhizobia employ the iron response regulator (Irr) to monitor and respond to the status of an iron-dependent process, namely, heme biosynthesis. This novel control mechanism allows iron homeostasis to be integrated with other cellular processes, and it permits differential control of iron regulon genes in a manner not readily achieved by Fur. Moreover, studies of Irr have defined a role for heme in conditional protein stability that has been subsequently described in eukaryotes. Finally, Irr-mediated control of iron metabolism may reflect a cellular strategy that accommodates a greater reliance on manganese.