Regulated Iron Siderophore Production of the Halophilic Archaeon Haloferax volcanii.

Natalie Niessen,Jörg Soppa

doi:10.3390/biom10071072

Abstract

Iron is part of many redox and other enzymes and, thus, it is essential for all living beings. Many oxic environments have extremely low concentrations of free iron. Therefore, many prokaryotic species evolved siderophores, i.e., small organic molecules that complex Fe3+ with very high affinity. Siderophores of bacteria are intensely studied, in contrast to those of archaea. The haloarchaeon Haloferax volcanii contains a gene cluster that putatively encodes siderophore biosynthesis genes, including four iron uptake chelate (iuc) genes. Underscoring this hypothesis, Northern blot analyses revealed that a hexacistronic transcript is generated that is highly induced under iron starvation. A quadruple iuc deletion mutant was generated, which had a growth defect solely at very low concentrations of Fe3+, not Fe2+. Two experimental approaches showed that the wild type produced and exported an Fe3+-specific siderophore under low iron concentrations, in contrast to the iuc deletion mutant. Bioinformatic analyses revealed that haloarchaea obtained the gene cluster by lateral transfer from bacteria and enabled the prediction of enzymatic functions of all six gene products. Notably, a biosynthetic pathway is proposed that starts with aspartic acid, uses several group donors and citrate, and leads to the hydroxamate siderophore Schizokinen.

Highlights

Iron is an essential element for all living beings
The genome of Haloferax volcanii contains four genes that are annotated as iuc genes based on the similarity of the encoded proteins to bacterial siderophore biosynthesis proteins [9]
The genome of H. volcanii contains four genes that are annotated as iuc genes, which could possibly encode enzymes involved in siderophore biosynthesis

Summary

Introduction

Iron is an essential element for all living beings It is, for example, a constitutive part of ion sulfur clusters, which are involved in the redox chemistry of many enzymes. Many aerobic microorganisms developed efficient iron chelatores, small organic molecules which are referred to as siderophores They are typically produced only at low extracellular iron concentrations, are secreted, and bind Fe3+ with high affinity. Many hosts developed iron-binding proteins (e.g., ferritin, transferrin) to sequester iron, thereby limiting microbial growth. To overcome this hurdle, many pathogenic microorganisms produce siderophores with high Fe3+ affinity to guarantee a sufficient iron supply in spite of the low intra-host concentration and, part of the pathogen–host interaction is a battle for iron [2]

Methods

Results

Discussion

Conclusion