Aspergillus fumigatus <i>Afssn3-Afssn8</i> Pair Reverse Regulates Azole Resistance by Conferring Extracellular Polysaccharide, Sphingolipid Pathway Intermediates, and Efflux Pumps to Biofilm

Abstract

Antifungal treatment is often ineffectual, partly because of biofilm formation. In this study, by using a combined forward and reverse genetic strategy, we identified that nucleus-localized AfSsn3 and its partner AfSsn8, which constitute a Cdk8-cyclin pair, are required for azole resistance in <i>Aspergillus fumigatus</i> Deletion of <i>Afssn3</i> led to increased absorption and utilization of glucose and amino acids. Interestingly, absorption and utilization of glucose accelerated the extracellular polysaccharide formation, while utilization of the amino acids serine, threonine, and glycine increased sphingolipid pathway intermediate accumulation. In addition, the absence of <i>Afssn3</i> induced the activity of the efflux pump proteins. These factors indicate the mature biofilm is responsible for the major mechanisms of <i>A. fumigatus</i> resistance to azoles in the Δ<i>Afssn3</i> mutant. Collectively, the loss of <i>Afssn3</i> led to two "barrier" layers between the intracellular and extracellular spaces, which consequently decreased drug penetration into the cell.