The divalent metal ion exporter IhpABC is required to maintain iron homeostasis under low to moderate environmental iron conditions in the bacterium Bradyrhizobium japonicum

• Published in: Molecular microbiology Vol. 121; no. 1; pp. 85 - 97
• Main Authors: Zhang, Fengyue, O'Brian, Mark R.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-01-2024
• Subjects: Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bradyrhizobium - genetics; Bradyrhizobium - metabolism; Bradyrhizobium japonicum; Cadmium; Efflux; Gene expression; Gene Expression Regulation, Bacterial - genetics; Homeostasis; Hydrogen peroxide; Iron; Iron - metabolism; iron export; Metal ions; Mutants; Phenotypes; RND exporter; Zinc chloride; iron metabolism; RND exporter; iron export; Bradyrhizobium japonicum
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.15198

Bacterial iron export mitigates high iron stress, but a role for it under lower iron conditions has not been established. MbfA is the high iron stress exporter in Bradyrhizobium japonicum. Here, we identify the ihpABC genes in a selection for secondary site mutations that suppress the poor growth phenotype of feoAB mutants defective in iron acquisition. IhpABC belongs to the RND tripartite efflux pump family. High iron conditions that derepress the mbfA gene partially rescued the growth of an ihpC mutant but reverted the feoB ihpC mutant to the feoB growth phenotype. The ihpA mutant grown under low iron conditions accumulated higher levels of iron compared to the wild type, and it displayed aberrant iron‐responsive gene expression. The mbfA mutant was more sensitive than the wild type to H2O2, but the ihpA mutant was not sensitive. The ihpA mutant accumulated more Zn, Co and Cd than was found in the wild type, and growth of the mutant was more sensitive to inhibition by ZnCl2, CoCl2 and CdCl2. The findings suggest that IhpABC is a divalent metal ion exporter that helps maintain iron homeostasis under low to moderate environmental iron levels. Thus, iron export is not limited to managing high iron stress.
Iron export is required to maintain iron homeostasis over a wide range, and not limited to high iron stress. IhpABC functions at lower iron concentrations, whereas MbfA is the high iron exporter in Bradyrhizobium japonicum. IhpABC is a divalent metal ion exporter. MbfA is specific for ferrous iron.