MOLECULAR MECHANISMS INVOLVED IN IRON HOMEOSTASIS OF PARACOCCIDIOIDES BRASILIENSIS

Elisa Flávia Luiz Cardoso Bailão (UFG); Mirelle Garcia Silva (UFG); Alexandre Melo Bailão (UFG); Célia Maria de Almeida Soares (UFG)

        For a range of microbial pathogens, iron is an essential micronutrient. Iron sequestration in response to infection is a demonstrated host defense mechanism, thus iron acquisition is important in the interplay between the host and pathogenic microbe. Although iron is required by most organisms, most environmental sources contain insoluble ferric iron, which can be reduced to ferrous iron by ferric reductases in the plasma membrane. The ferrous iron, then, can be either transported directly into the cell or be reoxidated to Fe⁺³ and be simultaneously internalized. On the other hand, excessive iron is toxic because iron reacts with oxygen to cause the formation of free radicals. So the iron homeostasis is an essential function that is generally tightly regulated in microorganisms. The goal of this study is the understanding of iron homeostasis in Paracoccidioides brasiliensis, a human pathogenic fungus. For that, we have done a homology based searching in P. brasiliensis structural genome databank (http://www.broadinstitute.org/annotation/genome/paracoccidioides_brasiliensis/MultiHome.html) for possible genes involved in the homeostasis maintenance. This homology analyses permitted the construction of an iron homeostasis model for this fungus. After, it was investigated the expression of ferric reductases (FRE), ferroxidases (FET), a mitochondrial iron carrier protein (MRS4), a mitochondrial matrix iron chaperone (YFH1), a putative vacuolar Fe⁺²/Mn⁺² transporter (CCC1) in the presence or absence of iron in different times by reverse transcription real-time PCR. Moreover, extracellular ferric reductase activity was identified by standardizing a qualitative solid-phase ferric reductase assay for this fungus. The results show that P. brasiliensis is able to reduce ferric iron and it has many mechanisms to maintain the normal intracellular iron levels. Therefore iron homeostasis is likely to be important factor to growth, survival and virulence of this fungus, as established for other pathogenic organisms.