Transcriptional analysis of developing Aspergillus fumigatus biofilms reveals metabolic shifts required for biofilm maintenance

Abstract

Aspergillus fumigatus is a filamentous fungus found in compost and soil that can cause invasive and/or chronic disease in a broad spectrum of individuals. Diagnosis and treatment of aspergillosis often occur during stages of infection when A. fumigatus has formed dense networks of hyphae within the lung. These dense hyphal networks are multicellular, encased in a layer of extracellular matrix, and have reduced susceptibility to contemporary antifungal drugs, characteristics which are defining features of a microbial biofilm. A mode of growth similar to these dense hyphal networks observed in vivo can be recapitulated in vitro using a static, submerged biofilm culture model. The mechanisms underlying filamentous fungal cell physiology at different stages of biofilm development remain to be defined. Here, we utilized an RNA sequencing approach to evaluate changes in transcript levels during A. fumigatus biofilm development. These analyses revealed an increase in transcripts associated with fermentation and a concomitant decrease in oxidative phosphorylation related transcripts. Further investigation revealed that ethanol and butanediol fermentation is important for mature biofilm biomass maintenance. Correspondingly, a gene (silG), a predicted transcription factor, was observed to also be required for mature biofilm biomass maintenance. Taken together, these data suggest temporal changes in A. fumigatus metabolism during biofilm development are required to maintain a fully mature biofilm. IMPORTANCEAspergillus fumigatus is the most common etiological agent of a collection of diseases termed aspergillosis. Invasive Pulmonary Aspergillosis (IPA), a severe form of aspergillosis, is highlighted by invasive growth of fungal hyphae into host lung tissue. Strains that are susceptible to antifungal therapies in vitro frequently fail to respond to treatment in vivo, resulting in high mortality rates even with treatment. It is now appreciated that this decreased antifungal efficacy in vivo is, in part, likely due to biofilm-like growth of the fungus. A. fumigatus biofilms have been shown to develop regions of limited oxygen availability that are hypothesized to induce cell quiescence and drug resistance. Understanding the mechanisms by which A. fumigatus induces, develops, and maintains biofilms to evade antifungal therapies is expected to illuminate biofilm-specific therapeutic targets. Here we present transcriptomics data of developing A. fumigatus biofilms and from these data define genes related to fungal fermentation and regulation of transcription important for maintenance of mature A. fumigatus biofilms.