Conservation and loss of a putative iron utilization gene cluster among genotypes of aspergillus flavus

Authors: Adhikari, Bishwo; Callicott, Kenneth; Cotty, Peter

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 1/9/2021
Publication URL: https://handle.nal.usda.gov/10113/7245091
Citation: Adhikari, B.N., Callicott, K.A., Cotty, P.J. 2021. Conservation and loss of a putative iron utilization gene cluster among genotypes of aspergillus flavus. Microorganisms. 9(1). Article 137. https://doi.org/10.3390/microorganisms9010137.
DOI: https://doi.org/10.3390/microorganisms9010137

Interpretive Summary: Aspergillus flavus genotypes vary in competitive ability. The most important tool for preventing aflatoxins in crops is a biological control that uses highly competitive atoxigenic isolates of A. flavus to competitively exclude aflatoxin producers. In order to select optimal next generation biocontrol agents we need to know the reason why some genotypes are more competitive. Iron is indispensable to life and many organisms utilize multiple pathways for iron uptake, utilization and storage in order to compete with other organisms. In the current study, genomes of A. flavus were explored for variation in iron utilization genes in order to determine if variation in mechanisms for iron utilization may be one cause of variation in competitive ability. The study revealed variation among A. flavus isolates in iron utilization genes. Variation in the iron genes suggests a mechanism for differences in competitive ability and may lead to development of at least one simple criterion for selection of competitive biocontrol agents

Technical Abstract: Iron is an essential component for growth and development of the vast majority of organisms. 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 mechanisms to utilize diverse pathways to uptake and use iron. In the current study, we identified and characterized an iron utilization gene cluster (IUC) in Aspergillus flavus, involved in iron uptake and utilization. Gene cluster analyses indicate A. flavus uses 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 the 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 gene cluster, which ranged from complete clusters to clusters disabled by multiple indels. The observed diversity of the IUC among A. flavus isolates, together with lack of similarity to iron uptake and utilization gene clusters of other Aspergilli, suggest that the IUC characterized in the current study could be unique and play important roles in adaptation. 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.