ABSTRACT: Selenium (Se) is an essential element for most organisms, yet outside of a narrow concentration range of sufficiency, both Se deficiency and Se toxicity are critical global problems. Diverse organisms are capable of promoting Se reduction-oxidation (redox) and methylation reactions that transform Se and alter its chemical speciation, bioavailability, and toxicity. Se transformation mechanisms in environmentally-relevant filamentous fungi, however, are poorly resolved. In this study using the non-model Ascomycota Paraphaeosphaeria sporulosa AP3s5-JAC2a, comparative transcriptomics, proteomics, and geochemical analyses were employed to identify the primary genes and proteins playing a role in Se transformation. Upon exposure to aqueous selenite (Se(IV)), altered expression profiles were assessed over time in relation to changes in Se bioproducts, such as intracellular and extracellular Se(0) nanoparticles, intracellular organoselenium compounds, and volatile, methylated Se compounds. Results showed that selenite uptake can occur via upregulated ABC and MFS transporters, and multiple mechanisms for Se(IV) reduction and Se(0) nanoparticle stabilization, such as glutathione reductase and oxidoreductases enzymes, were identified. Multiple methyltransferases that promote Se volatilization and pathways for vesicle formation and exocytosis, likely for Se(0) export, were also identified. Notably, proteins involved in oxidative stress defense (e.g., catalase, peroxidase, superoxide dismutase) were induced by Se exposure. These data contribute to a more complete understanding of previously hypothesized or unresolved mechanisms behind Se transformations in filamentous fungi. On a global scale, this work sheds new light on ecological strategies for detoxification and reveals the genetic mechanisms required for biotechnological applications of fungal-produced Se products.
