Role of a Fur homolog in iron metabolism in Nitrosomonas europaea

Neeraja Vajrala,Peter J Bottomley,Daniel J Arp,Luis A Sayavedra-Soto

doi:10.1186/1471-2180-11-37

Abstract

BackgroundIn response to environmental iron concentrations, many bacteria coordinately regulate transcription of genes involved in iron acquisition via the ferric uptake regulation (Fur) system. The genome of Nitrosomonas europaea, an ammonia-oxidizing bacterium, carries three genes (NE0616, NE0730 and NE1722) encoding proteins belonging to Fur family.ResultsOf the three N. europaea fur homologs, only the Fur homolog encoded by gene NE0616 complemented the Escherichia coli H1780 fur mutant. A N. europaea fur:kanP mutant strain was created by insertion of kanamycin-resistance cassette in the promoter region of NE0616 fur homolog. The total cellular iron contents of the fur:kanP mutant strain increased by 1.5-fold compared to wild type when grown in Fe-replete media. Relative to the wild type, the fur:kanP mutant exhibited increased sensitivity to iron at or above 500 μM concentrations. Unlike the wild type, the fur:kanP mutant was capable of utilizing iron-bound ferrioxamine without any lag phase and showed over expression of several outer membrane TonB-dependent receptor proteins irrespective of Fe availability.ConclusionsOur studies have clearly indicated a role in Fe regulation by the Fur protein encoded by N. europaea NE0616 gene. Additional studies are required to fully delineate role of this fur homolog.

Highlights

In response to environmental iron concentrations, many bacteria coordinately regulate transcription of genes involved in iron acquisition via the ferric uptake regulation (Fur) system
Sequence analysis of N. europaea fur homologs The three N. europaea Fur-like repressors encoded by NE0616, NE0730, NE1722 are only distantly related to each other with 25% to 35% amino acid identity
Binding Site 1 represents the putative iron binding regulatory site and is coordinated by amino acids H86, D88, E107, and H124 and Site 2 is coordinated by H32, E80, H89 and E100 [19]. All these residues are conserved only in the N. europaea NE0616 Fur homolog but not in Fur homologs encoded by NE0730 and NE1722 (Figure 1)

Summary

Introduction

In response to environmental iron concentrations, many bacteria coordinately regulate transcription of genes involved in iron acquisition via the ferric uptake regulation (Fur) system. The genome of Nitrosomonas europaea, an ammonia-oxidizing bacterium, carries three genes (NE0616, NE0730 and NE1722) encoding proteins belonging to Fur family. Several bacteria are known to regulate their iron acquisition systems via Fur (ferric uptake regulator) [2,3,4,5]. Fur is a sequence-specific DNAbinding protein that acts mainly as a negative regulator of transcription in vivo by complexing with ferrous (Fe2+) ion to repress the expression of iron-regulated genes [6]. N. europaea responds to iron limitation by elevating production of Fe3+-siderophore receptors normally repressed under iron-replete conditions [13,14]. Sequence annotation of N. europaea genome revealed three genes encoding fur homologs (NE0616, NE0730, NE1722) that contain characteristic Fur domains [9]

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