Pathogenicity of Aspergillus species

Dr Elaine Bignell studies pathogenicity of Aspergillus species, in particular, the mechanisms by which these fungi sense and adapt to the host environment. Aspergillus pH- sensing and siderophore-assisted iron uptake are examples of such mechanisms which have recently been characterised during the infection process using murine modelling of Aspergillus infection and fungal molecular genetics.

Fungal Pathogenesis

Aspergillus fumigatus is a common mould whose spores are a component of the normal airborne flora. Immune dysfunction permits developmental growth of inhaled spores in the human lung causing aspergillosis, a significant threat to human health in the form of allergic, and life-threatening invasive infections. In order to rationalise diagnostic and therapeutic mediation of the diverse host-pathogen interactions supporting A. fumigatus infection we are using molecular genetics, infection modelling, transcriptional profiling and protein interaction modelling to chronicle the founding molecular events in A. fumigatus pathogenesis.

Fig: Invasion of murine pulmonary epithelium by Aspergillus hyphae

Sensory deprivation as a means to prevent A. fumigatus infection

The remarkable versatility of A. fumigatus with respect to the environments it can successfully inhabit is a primary asset for pathogenicity. Mutational restriction of nutrient acquisition, siderophore biosynthesis, pH adaptation and amino acid biosynthesis can prevent virulence in experimental infections. At the earliest time points of developmental growth within the mammalian host multiple sensory mechanisms are essential for appropriate adaptation and subsequent invasive growth. The ability to specifically block such mechanisms would provide a means to prevent fungal growth within the host.

Alkaline adaptation and A. fumigatus infection

A. fumigatus can support growth across a broad range of environmental pH values. Adapting to altering pH conditions requires appropriate regulation of many cellular functions, not least transport and uptake of nutrients, reprogramming of transporter protein and permease functions at the cell surface, uptake and export of metal ions, pH sensing and intracellular signalling. Mutational perturbation of pH adaptation in the model ascomycete, A. nidulans, abolishes virulence in infection models. We are now characterising the role of pH adaptation in A. fumigatus using a refined gene deletion methodology – the split biselectable marker system.

Calcium sensing and A. fumigatus infection

Perturbation of calcium signalling has been associated with antifungal activity of several existing drugs, such as the antiarrythmic drug amiodarone, and the immunosuppressant cyclosporine. Opportunities to prevent fungal growth within the mammalian host may therefore arise from further characterisation of calcium signalling in this organism, and may well act synergistically with existing drugs. We are using microarray transcription profiling to identify novel components of the A. fumigatus calcium signalling and homeostatic machinery and molecular genetic approaches to determine their role in virulence.

Genome-wide transcriptional profiling

To understand the environmental cues prompting A. fumigatus adaptation to the mammalian host we have developed a methodology to isolate and amplify A. fumigatus RNA from infection models. In collaboration with Bill Nierman’s research group at the J Craig Venter Institute we are using this approach to characterise fungal gene expression within the host niche. Microarray hybridisation with amplified RNA conveys a highly detailed and reproducible account of A. fumigatus gene activity, directly from the site of infection. We have used this tool to identify A. fumigatus genes which are ‘switched on’ during initiation of infection. 

Modelling protein interactions at the A. fumigatus cellular boundary

We are developing a new proteomic tool for identifying A. fumigatus membrane-bound protein-protein interactions the virulence-essential pH-sensing A. fumigatus PalH and PalI proteins as prototypes. This will provide a screening platform for future identification of inhibitors of characterised A. fumigatus membrane protein-protein interactions and, ultimately, a means to screen for potential inhibitors of A. fumigatus growth in a high throughput manner.

Tracking A. fumigatus proteins and small molecules during mammalian infection

A. fumigatus proteins have diverse roles in the infection process, from degrading lung epithelial tissue to provoking allergic reactions in sensitized individuals. We are developing methodologies to simultaneously track multiple fungal proteins during during the initiating stages of A. fumigatus infection to define the enzyme activities involved and therefore seek means to inhibit their production/activity.

Regulatory control of integron-mediated antibiotic resistance

For further details on this research stream, please see Dr Bignell's page on the Centre for Molecular Bacteriology and Infection website.

Recent Publications

Jamal A; Bignell EM; Coutts RH. (Oct 2010). Complete nucleotide sequences of four dsRNAs associated with a new chrysovirus infecting Aspergillus fumigatus. Virus Res. 153:64-70. DOI.

Cairns T; Minuzzi F; Bignell E. (Jun 2010). The host-infecting fungal transcriptome. FEMS MICROBIOL LETT. 307:1-11. DOI.

Han KH; Chun YH; Figueiredo BDP; Soriani FM; Savoldi M; Almeida A; Rodrigues F; Cairns CT; et al. (May 2010). The conserved and divergent roles of carbonic anhydrases in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans (vol 75, pg 1372, 2010). MOL MICROBIOL. 76:802-802.

Chamilos G; Bignell EM; Schrettl M; Lewis RE; Leventakos K; May GS; Haas H; Kontoyiannis DP. (May 2010). Exploring the concordance of Aspergillus fumigatus pathogenicity in mice and Toll-deficient flies. Med Mycol. 48:506-510. DOI.

Bignell E. (8 Mar 2010). Aspergillus: Molecular Biology and Genomics. By Masayuki Machida and Katsuya Gomi (Eds.). Biotechnol J. 5:336-337. DOI.

Han KH; Chun YH; Figueiredo BDEC; Soriani FM; Savoldi M; Almeida A; Rodrigues F; Cairns CT; et al. (Mar 2010). The conserved and divergent roles of carbonic anhydrases in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans. Mol Microbiol. 75:1372-1388. DOI.

Bergmann A; Hartmann T; Cairns T; Bignell EM; Krappmann S. (Sep 2009). A Regulator of Aspergillus fumigatus Extracellular Proteolytic Activity Is Dispensable for Virulence. INFECT IMMUN. 77:4041-4050. DOI.

Armstrong-James DP; Turnbull SA; Teo I; Stark J; Rogers NJ; Rogers TR; Bignell E; Haynes K. (15 Oct 2009). Impaired interferon-gamma responses, increased interleukin-17 expression, and a tumor necrosis factor-alpha transcriptional program in invasive aspergillosis. J Infect Dis. 200:1341-1351. DOI.

McDonagh A; Fedorova ND; Crabtree J; Yu Y; Kim S; Chen D; Loss O; Cairns T; et al. (2008). Sub-telomere directed gene expression during initiation of invasive aspergillosis. PLoS Pathog. 4:e1000154. DOI.