Conservation and Loss of a Putative Iron Utilization Gene Cluster among Genotypes of Aspergillus flavus.

Bishwo N Adhikari,Kenneth A Callicott,Peter J Cotty

doi:10.3390/microorganisms9010137

Bishwo N Adhikari, Kenneth A Callicott + Show 1 more

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https://doi.org/10.3390/microorganisms9010137

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Abstract

Iron is an essential component for growth and development. Despite relative abundance in the environment, bioavailability of iron is limited due to oxidation by atmospheric oxygen into insoluble ferric iron. Filamentous fungi have developed diverse pathways to uptake and use iron. In the current study, a putative iron utilization gene cluster (IUC) in Aspergillus flavus was identified and characterized. Gene analyses indicate A. flavus may use reductive as well as siderophore-mediated iron uptake and utilization pathways. The ferroxidation and iron permeation process, in which iron transport depends on the coupling of these two activities, mediates the reductive pathway. The IUC identified in this work includes six genes and is located in a highly polymorphic region of the genome. Diversity among A. flavus genotypes is manifested in the structure of the IUC, which ranged from complete deletion to a region disabled by multiple indels. Molecular profiling of A. flavus populations suggests lineage-specific loss of IUC. The observed variation among A. flavus genotypes in iron utilization and the lineage-specific loss of the iron utilization genes in several A. flavus clonal lineages provide insight on evolution of iron acquisition and utilization within Aspergillus section Flavi. The potential divergence in capacity to acquire iron should be taken into account when selecting A. flavus active ingredients for biocontrol in niches where climate change may alter iron availability.

Highlights

Iron is an essential element for the majority of organisms, where it serves as cofactor for enzymatic reactions and catalyst for electron transport systems
In order to identify the structural variants in the five initial A. flavus genotypes, genome sequences were compared with A. oryzae RIB40 reference [56]
Genome-wide alignment indicates presence of only one such group of genes in the five initial A. flavus isolates, A. oryzae, and A. nomius while A. fumigatus, A. nidulans, and A. niger had no region with significant similarity

Summary

Introduction

Iron is an essential element for the majority of organisms, where it serves as cofactor for enzymatic reactions and catalyst for electron transport systems. Despite relative abundance in most environments, bioavailability of iron is limited due to oxidation by atmospheric oxygen into insoluble ferric (Fe3+ ) oxyhydroxides, and iron-dependent organisms must reduce ferric iron to its ferrous (Fe2+ ) state prior to absorbtion. Cellular iron homeostasis is designed to tightly regulate the iron supply to prevent excess accumulation. Because of the twin needs of iron uptake and iron regulation, iron-dependent organisms have evolved tightly regulated acquisition and storage strategies [4,5], and iron often serves as a signal for gene expression involved in iron uptake and storage. Many prokaryotic and eukaryotic pathogens require iron for virulence [6,7] and employ multiple pathways for iron uptake, utilization, and storage [8]

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